Chapter 24. APIs and Libraries

Table of Contents

24.1. libmysqld, the Embedded MySQL Server Library
24.1.1. Overview of the Embedded MySQL Server Library
24.1.2. Compiling Programs with libmysqld
24.1.3. Restrictions When Using the Embedded MySQL Server
24.1.4. Options with the Embedded Server
24.1.5. Embedded Server Examples
24.1.6. Licensing the Embedded Server
24.2. MySQL C API
24.2.1. C API Data types
24.2.2. C API Function Overview
24.2.3. C API Function Descriptions
24.2.4. C API Prepared Statements
24.2.5. C API Prepared Statement Data types
24.2.6. C API Prepared Statement Function Overview
24.2.7. C API Prepared Statement Function Descriptions
24.2.8. C API Prepared statement problems
24.2.9. C API Handling of Multiple Statement Execution
24.2.10. C API Handling of Date and Time Values
24.2.11. C API Threaded Function Descriptions
24.2.12. C API Embedded Server Function Descriptions
24.2.13. Common Questions and Problems When Using the C API
24.2.14. Building Client Programs
24.2.15. How to Make a Threaded Client
24.3. MySQL PHP API
24.3.1. Common Problems with MySQL and PHP
24.3.2. Enabling Both mysql and mysqli in PHP
24.4. MySQL Perl API
24.5. MySQL C++ API
24.6. MySQL Python API
24.7. MySQL Tcl API
24.8. MySQL Eiffel Wrapper
24.9. MySQL Program Development Utilities
24.9.1. msql2mysql — Convert mSQL Programs for Use with MySQL
24.9.2. mysql_config — Get Compile Options for Compiling Clients

This chapter describes the APIs available for MySQL, where to get them, and how to use them. The C API is the most extensively covered, because it was developed by the MySQL team, and is the basis for most of the other APIs. This chapter also covers the libmysqld library (the embedded server), as well as some programs that are useful for application developers.

24.1. libmysqld, the Embedded MySQL Server Library

24.1.1. Overview of the Embedded MySQL Server Library

The embedded MySQL server library makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.

The embedded server library is based on the client/server version of MySQL, which is written in C/C++. Consequently, the embedded server also is written in C/C++. There is no embedded server available in other languages.

The API is identical for the embedded MySQL version and the client/server version. To change an old threaded application to use the embedded library, you normally only have to add calls to the following functions:

FunctionWhen to Call
mysql_server_init()Should be called before any other MySQL function is called, preferably early in the main() function.
mysql_server_end()Should be called before your program exits.
mysql_thread_init()Should be called in each thread you create that accesses MySQL.
mysql_thread_end()Should be called before calling pthread_exit()

Then you must link your code with libmysqld.a instead of libmysqlclient.a.

The mysql_server_xxx() functions are also included in libmysqlclient.a to allow you to change between the embedded and the client/server version by just linking your application with the right library. See Section 24.2.12.1, “mysql_server_init().

One difference between the embedded server and the standalone server is that for the embedded server, authentication for connections is disabled by default. To use authentication for the embedded server, specify the --with-embedded-privilege-control option when you invoke configure to configure your MySQL distribution.

24.1.2. Compiling Programs with libmysqld

To get a libmysqld library you should configure MySQL with the --with-embedded-server option. See Section 2.9.2, “Typical configure Options”.

When you link your program with libmysqld, you must also include the system-specific pthread libraries and some libraries that the MySQL server uses. You can get the full list of libraries by executing mysql_config --libmysqld-libs.

The correct flags for compiling and linking a threaded program must be used, even if you do not directly call any thread functions in your code.

To compile a C program to include the necessary files to embed the MySQL server library into a compiled version of a program, use the GNU C compiler (gcc). The compiler will need to know where to find various files and need instructions on how to compile the program. The following example shows how a program could be compiled from the command line:

gcc mysql_test.c -o mysql_test -lz \
`/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Immediately following the gcc command is the name of the uncompiled C program file. After it, the -o option is given to indicate that the file name that follows is the name that the compiler is to give to the output file, the compiled program. The next line of code tells the compiler to obtain the location of the include files and libraries and other settings for the system on which it's compiled. Because of a problem with mysql_config, the option -lz (for compression) is added here. The mysql_config piece is contained in backticks, not single quotes.

24.1.3. Restrictions When Using the Embedded MySQL Server

The embedded server has the following limitations:

  • No user-defined functions (UDFs).

  • No stack trace on core dump.

  • You cannot set this up as a master or a slave (no replication).

  • Very large result sets may be unusable on low memory systems.

  • You cannot connect to an embedded server from an outside process with sockets or TCP/IP. However, you can connect to an intermediate application, which in turn can connect to an embedded server on the behalf of a remote client or outside process.

Some of these limitations can be changed by editing the mysql_embed.h include file and recompiling MySQL.

24.1.4. Options with the Embedded Server

Any options that may be given with the mysqld server daemon, may be used with an embedded server library. Server options may be given in an array as an argument to the mysql_server_init(), which initializes the server. They also may be given in an option file like my.cnf. To specify an option file for a C program, use the --defaults-file option as one of the elements of the second argument of the mysql_server_init() function. See Section 24.2.12.1, “mysql_server_init(), for more information on the mysql_server_init() function.

Using option files can make it easier to switch between a client/server application and one where MySQL is embedded. Put common options under the [server] group. These are read by both MySQL versions. Client/server-specific options should go under the [mysqld] section. Put options specific to the embedded MySQL server library in the [embedded] section. Options specific to applications go under section labeled [ApplicationName_SERVER]. See Section 4.3.2, “Using Option Files”.

24.1.5. Embedded Server Examples

These two example programs should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes are needed, mostly with file paths. These examples are designed to give enough details for you to understand the problem, without the clutter that is a necessary part of a real application. The first example is very straightforward. The second example is a little more advanced with some error checking. The first is followed by a command-line entry for compiling the program. The second is followed by a GNUmake file that may be used for compiling instead.

Example 1

test1_libmysqld.c

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include "mysql.h"

MYSQL *mysql;
MYSQL_RES *results;
MYSQL_ROW record;

static char *server_options[] = \
       { "mysql_test", "--defaults-file=my.cnf", NULL };
int num_elements = (sizeof(server_options) / sizeof(char *)) - 1;

static char *server_groups[] = { "libmysqld_server", 
                                 "libmysqld_client", NULL };

int main(void)
{
   mysql_server_init(num_elements, server_options, server_groups);
   mysql = mysql_init(NULL);
   mysql_options(mysql, MYSQL_READ_DEFAULT_GROUP, "libmysqld_client");
   mysql_options(mysql, MYSQL_OPT_USE_EMBEDDED_CONNECTION, NULL);

   mysql_real_connect(mysql, NULL,NULL,NULL, "database1", 0,NULL,0);

   mysql_query(mysql, "SELECT column1, column2 FROM table1");

   results = mysql_store_result(mysql);

   while((record = mysql_fetch_row(results))) {
      printf("%s - %s \n", record[0], record[1]);
   }

   mysql_free_result(results);
   mysql_close(mysql);
   mysql_server_end();

   return 0;
}

Here is the command line for compiling the above program:

gcc test1_libmysqld.c -o test1_libmysqld -lz \
 `/usr/local/mysql/bin/mysql_config --include --libmysqld-libs`

Example 2

To try out the example, create an test2_libmysqld directory at the same level as the MySQL source directory. Save the test2_libmysqld.c source and the GNUmakefile in the directory, and run GNU make from inside the test2_libmysqld directory.

test2_libmysqld.c

/*
 * A simple example client, using the embedded MySQL server library
*/

#include <mysql.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

MYSQL *db_connect(const char *dbname);
void db_disconnect(MYSQL *db);
void db_do_query(MYSQL *db, const char *query);

const char *server_groups[] = {
  "test2_libmysqld_SERVER", "embedded", "server", NULL
};

int
main(int argc, char **argv)
{
  MYSQL *one, *two;

  /* mysql_server_init() must be called before any other mysql
   * functions.
   *
   * You can use mysql_server_init(0, NULL, NULL), and it
   * initializes the server using groups = {
   *   "server", "embedded", NULL
   *  }.
   *
   * In your $HOME/.my.cnf file, you probably want to put:

[test2_libmysqld_SERVER]
language = /path/to/source/of/mysql/sql/share/english

   * You could, of course, modify argc and argv before passing
   * them to this function.  Or you could create new ones in any
   * way you like.  But all of the arguments in argv (except for
   * argv[0], which is the program name) should be valid options
   * for the MySQL server.
   *
   * If you link this client against the normal mysqlclient
   * library, this function is just a stub that does nothing.
   */
  mysql_server_init(argc, argv, (char **)server_groups);

  one = db_connect("test");
  two = db_connect(NULL);

  db_do_query(one, "SHOW TABLE STATUS");
  db_do_query(two, "SHOW DATABASES");

  mysql_close(two);
  mysql_close(one);

  /* This must be called after all other mysql functions */
  mysql_server_end();

  exit(EXIT_SUCCESS);
}

static void
die(MYSQL *db, char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  (void)putc('\n', stderr);
  if (db)
    db_disconnect(db);
  exit(EXIT_FAILURE);
}

MYSQL *
db_connect(const char *dbname)
{
  MYSQL *db = mysql_init(NULL);
  if (!db)
    die(db, "mysql_init failed: no memory");
  /*
   * Notice that the client and server use separate group names.
   * This is critical, because the server does not accept the
   * client's options, and vice versa.
   */
  mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test2_libmysqld_CLIENT");
  if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0))
    die(db, "mysql_real_connect failed: %s", mysql_error(db));

  return db;
}

void
db_disconnect(MYSQL *db)
{
  mysql_close(db);
}

void
db_do_query(MYSQL *db, const char *query)
{
  if (mysql_query(db, query) != 0)
    goto err;

  if (mysql_field_count(db) > 0)
  {
    MYSQL_RES   *res;
    MYSQL_ROW    row, end_row;
    int num_fields;

    if (!(res = mysql_store_result(db)))
      goto err;
    num_fields = mysql_num_fields(res);
    while ((row = mysql_fetch_row(res)))
    {
      (void)fputs(">> ", stdout);
      for (end_row = row + num_fields; row < end_row; ++row)
        (void)printf("%s\t", row ? (char*)*row : "NULL");
      (void)fputc('\n', stdout);
    }
    (void)fputc('\n', stdout);
    mysql_free_result(res);
  }
  else
    (void)printf("Affected rows: %lld\n", mysql_affected_rows(db));

  return;

err:
  die(db, "db_do_query failed: %s [%s]", mysql_error(db), query);
}

GNUmakefile

# This assumes the MySQL software is installed in /usr/local/mysql
inc      := /usr/local/mysql/include/mysql
lib      := /usr/local/mysql/lib

# If you have not installed the MySQL software yet, try this instead
#inc      := $(HOME)/mysql-5.1/include
#lib      := $(HOME)/mysql-5.1/libmysqld

CC       := gcc
CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT
CFLAGS   := -g -W -Wall
LDFLAGS  := -static
# You can change -lmysqld to -lmysqlclient to use the
# client/server library
LDLIBS    = -L$(lib) -lmysqld -lz -lm -lcrypt

ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null))
# FreeBSD
LDFLAGS += -pthread
else
# Assume Linux
LDLIBS += -lpthread
endif

# This works for simple one-file test programs
sources := $(wildcard *.c)
objects := $(patsubst %c,%o,$(sources))
targets := $(basename $(sources))

all: $(targets)

clean:
        rm -f $(targets) $(objects) *.core

24.1.6. Licensing the Embedded Server

We encourage everyone to promote free software by releasing code under the GPL or a compatible license. For those who are not able to do this, another option is to purchase a commercial license for the MySQL code from MySQL AB. For details, please see http://www.mysql.com/company/legal/licensing/.

24.2. MySQL C API

The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.

Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.

Most of the other client APIs (all except Connector/J and Connector/NET) use the mysqlclient library to communicate with the MySQL server. This means that, for example, you can take advantage of many of the same environment variables that are used by other client programs, because they are referenced from the library. See Chapter 8, Client and Utility Programs, for a list of these variables.

The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16KB) is automatically increased up to the maximum size (the maximum is 16MB). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous statements and communication packets.

The communication buffer must be large enough to contain a single SQL statement (for client-to-server traffic) and one row of returned data (for server-to-client traffic). Each thread's communication buffer is dynamically enlarged to handle any query or row up to the maximum limit. For example, if you have BLOB values that contain up to 16MB of data, you must have a communication buffer limit of at least 16MB (in both server and client). The client's default maximum is 16MB, but the default maximum in the server is 1MB. You can increase this by changing the value of the max_allowed_packet parameter when the server is started. See Section 7.5.2, “Tuning Server Parameters”.

The MySQL server shrinks each communication buffer to net_buffer_length bytes after each query. For clients, the size of the buffer associated with a connection is not decreased until the connection is closed, at which time client memory is reclaimed.

For programming with threads, see Section 24.2.15, “How to Make a Threaded Client”. For creating a standalone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see Section 24.1, “libmysqld, the Embedded MySQL Server Library”.

24.2.1. C API Data types

  • MYSQL

    This structure represents a handle to one database connection. It is used for almost all MySQL functions. You should not try to make a copy of a MYSQL structure. There is no guarantee that such a copy will be usable.

  • MYSQL_RES

    This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section.

  • MYSQL_ROW

    This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row().

  • MYSQL_FIELD

    This structure contains information about a field, such as the field's name, type, and size. Its members are described in more detail here. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure.

  • MYSQL_FIELD_OFFSET

    This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.

  • my_ulonglong

    The type used for the number of rows and for mysql_affected_rows(), mysql_num_rows(), and mysql_insert_id(). This type provides a range of 0 to 1.84e19.

    On some systems, attempting to print a value of type my_ulonglong does not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:

    printf ("Number of rows: %lu\n", 
            (unsigned long) mysql_num_rows(result));
    
  • my_bool

    A boolean type, for values that are true (non-zero) or false (zero).

The MYSQL_FIELD structure contains the members listed here:

  • char * name

    The name of the field, as a null-terminated string. If the field was given an alias with an AS clause, the value of name is the alias.

  • char * org_name

    The name of the field, as a null-terminated string. Aliases are ignored.

  • char * table

    The name of the table containing this field, if it isn't a calculated field. For calculated fields, the table value is an empty string. If the table was given an alias with an AS clause, the value of table is the alias. If the column is selected from a view, table names the view.

  • char * org_table

    The name of the table, as a null-terminated string. Aliases are ignored. If the column is selected from a view, org_table names the underlying table.

  • char * db

    The name of the database that the field comes from, as a null-terminated string. If the field is a calculated field, db is an empty string.

  • char * catalog

    The catalog name. This value is always "def".

  • char * def

    The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields().

  • unsigned long length

    The width of the field, as specified in the table definition.

  • unsigned long max_length

    The maximum width of the field for the result set (the length of the longest field value for the rows actually in the result set). If you use mysql_store_result() or mysql_list_fields(), this contains the maximum length for the field. If you use mysql_use_result(), the value of this variable is zero.

  • unsigned int name_length

    The length of name.

  • unsigned int org_name_length

    The length of org_name.

  • unsigned int table_length

    The length of table.

  • unsigned int org_table_length

    The length of org_table.

  • unsigned int db_length

    The length of db.

  • unsigned int catalog_length

    The length of catalog.

  • unsigned int def_length

    The length of def.

  • unsigned int flags

    Different bit-flags for the field. The flags value may have zero or more of the following bits set:

    Flag ValueFlag Description
    NOT_NULL_FLAGField can't be NULL
    PRI_KEY_FLAGField is part of a primary key
    UNIQUE_KEY_FLAGField is part of a unique key
    MULTIPLE_KEY_FLAGField is part of a non-unique key
    UNSIGNED_FLAGField has the UNSIGNED attribute
    ZEROFILL_FLAGField has the ZEROFILL attribute
    BINARY_FLAGField has the BINARY attribute
    AUTO_INCREMENT_FLAGField has the AUTO_INCREMENT attribute
    ENUM_FLAGField is an ENUM (deprecated)
    SET_FLAGField is a SET (deprecated)
    BLOB_FLAGField is a BLOB or TEXT (deprecated)
    TIMESTAMP_FLAGField is a TIMESTAMP (deprecated)

    Use of the BLOB_FLAG, ENUM_FLAG, SET_FLAG, and TIMESTAMP_FLAG flags is deprecated because they indicate the type of a field rather than an attribute of its type. It is preferable to test field->type against MYSQL_TYPE_BLOB, MYSQL_TYPE_ENUM, MYSQL_TYPE_SET, or MYSQL_TYPE_TIMESTAMP instead.

    The following example illustrates a typical use of the flags value:

    if (field->flags & NOT_NULL_FLAG)
        printf("Field can't be null\n");
    

    You may use the following convenience macros to determine the boolean status of the flags value:

    Flag StatusDescription
    IS_NOT_NULL(flags)True if this field is defined as NOT NULL
    IS_PRI_KEY(flags)True if this field is a primary key
    IS_BLOB(flags)True if this field is a BLOB or TEXT (deprecated; test field->type instead)
  • unsigned int decimals

    The number of decimals for numeric fields.

  • unsigned int charsetnr

    The character set number for the field.

  • enum enum_field_types type

    The type of the field. The type value may be one of the MYSQL_TYPE_ symbols shown in the following table.

    Type ValueType Description
    MYSQL_TYPE_TINYTINYINT field
    MYSQL_TYPE_SHORTSMALLINT field
    MYSQL_TYPE_LONGINTEGER field
    MYSQL_TYPE_INT24MEDIUMINT field
    MYSQL_TYPE_LONGLONGBIGINT field
    MYSQL_TYPE_DECIMALDECIMAL or NUMERIC field
    MYSQL_TYPE_NEWDECIMALPrecision math DECIMAL or NUMERIC
    MYSQL_TYPE_FLOATFLOAT field
    MYSQL_TYPE_DOUBLEDOUBLE or REAL field
    MYSQL_TYPE_BITBIT field
    MYSQL_TYPE_TIMESTAMPTIMESTAMP field
    MYSQL_TYPE_DATEDATE field
    MYSQL_TYPE_TIMETIME field
    MYSQL_TYPE_DATETIMEDATETIME field
    MYSQL_TYPE_YEARYEAR field
    MYSQL_TYPE_STRINGCHAR or BINARY field
    MYSQL_TYPE_VAR_STRINGVARCHAR or VARBINARY field
    MYSQL_TYPE_BLOBBLOB or TEXT field (use max_length to determine the maximum length)
    MYSQL_TYPE_SETSET field
    MYSQL_TYPE_ENUMENUM field
    MYSQL_TYPE_GEOMETRYSpatial field
    MYSQL_TYPE_NULLNULL-type field
    MYSQL_TYPE_CHARDeprecated; use MYSQL_TYPE_TINY instead

    You can use the IS_NUM() macro to test whether a field has a numeric type. Pass the type value to IS_NUM() and it evaluates to TRUE if the field is numeric:

    if (IS_NUM(field->type))
        printf("Field is numeric\n");
    

    To distinguish between binary and non-binary data for string data types, check whether the charsetnr value is 63. If so, the character set is binary, which indicates binary rather than non-binary data. This is how to distinguish between BINARY and CHAR, VARBINARY and VARCHAR, and BLOB and TEXT.

24.2.2. C API Function Overview

The functions available in the C API are summarized here and described in greater detail in a later section. See Section 24.2.3, “C API Function Descriptions”.

FunctionDescription
mysql_affected_rows()Returns the number of rows changed/deleted/inserted by the last UPDATE, DELETE, or INSERT query.
mysql_autocommit()Toggles autocommit mode on/off.
mysql_change_user()Changes user and database on an open connection.
mysql_close()Closes a server connection.
mysql_commit()Commits the transaction.
mysql_connect()Connects to a MySQL server. This function is deprecated; use mysql_real_connect() instead.
mysql_create_db()Creates a database. This function is deprecated; use the SQL statement CREATE DATABASE instead.
mysql_data_seek()Seeks to an arbitrary row number in a query result set.
mysql_debug()Does a DBUG_PUSH with the given string.
mysql_drop_db()Drops a database. This function is deprecated; use the SQL statement DROP DATABASE instead.
mysql_dump_debug_info()Makes the server write debug information to the log.
mysql_eof()Determines whether the last row of a result set has been read. This function is deprecated; mysql_errno() or mysql_error() may be used instead.
mysql_errno()Returns the error number for the most recently invoked MySQL function.
mysql_error()Returns the error message for the most recently invoked MySQL function.
mysql_escape_string()Escapes special characters in a string for use in an SQL statement.
mysql_fetch_field()Returns the type of the next table field.
mysql_fetch_field_direct()Returns the type of a table field, given a field number.
mysql_fetch_fields()Returns an array of all field structures.
mysql_fetch_lengths()Returns the lengths of all columns in the current row.
mysql_fetch_row()Fetches the next row from the result set.
mysql_field_seek()Puts the column cursor on a specified column.
mysql_field_count()Returns the number of result columns for the most recent statement.
mysql_field_tell()Returns the position of the field cursor used for the last mysql_fetch_field().
mysql_free_result()Frees memory used by a result set.
mysql_get_client_info()Returns client version information as a string.
mysql_get_client_version()Returns client version information as an integer.
mysql_get_host_info()Returns a string describing the connection.
mysql_get_server_version()Returns version number of server as an integer.
mysql_get_proto_info()Returns the protocol version used by the connection.
mysql_get_server_info()Returns the server version number.
mysql_info()Returns information about the most recently executed query.
mysql_init()Gets or initializes a MYSQL structure.
mysql_insert_id()Returns the ID generated for an AUTO_INCREMENT column by the previous query.
mysql_kill()Kills a given thread.
mysql_library_end()Finalize MySQL C API library.
mysql_library_init()Initialize MySQL C API library.
mysql_list_dbs()Returns database names matching a simple regular expression.
mysql_list_fields()Returns field names matching a simple regular expression.
mysql_list_processes()Returns a list of the current server threads.
mysql_list_tables()Returns table names matching a simple regular expression.
mysql_more_results()Checks whether any more results exist.
mysql_next_result()Returns/initiates the next result in multiple-statement executions.
mysql_num_fields()Returns the number of columns in a result set.
mysql_num_rows()Returns the number of rows in a result set.
mysql_options()Sets connect options for mysql_connect().
mysql_ping()Checks whether the connection to the server is working, reconnecting as necessary.
mysql_query()Executes an SQL query specified as a null-terminated string.
mysql_real_connect()Connects to a MySQL server.
mysql_real_escape_string()Escapes special characters in a string for use in an SQL statement, taking into account the current character set of the connection.
mysql_real_query()Executes an SQL query specified as a counted string.
mysql_refresh()Flush or reset tables and caches.
mysql_reload()Tells the server to reload the grant tables.
mysql_rollback()Rolls back the transaction.
mysql_row_seek()Seeks to a row offset in a result set, using value returned from mysql_row_tell().
mysql_row_tell()Returns the row cursor position.
mysql_select_db()Selects a database.
mysql_server_end()Finalize embedded server library.
mysql_server_init()Initialize embedded server library.
mysql_set_local_infile_default()Set the LOAD DATA LOCAL INFILE handler callbacks to their default values.
mysql_set_local_infile_handler()Install application-specific LOAD DATA LOCAL INFILE handler callbacks.
mysql_set_server_option()Sets an option for the connection (like multi-statements).
mysql_sqlstate()Returns the SQLSTATE error code for the last error.
mysql_shutdown()Shuts down the database server.
mysql_stat()Returns the server status as a string.
mysql_store_result()Retrieves a complete result set to the client.
mysql_thread_id()Returns the current thread ID.
mysql_thread_safe()Returns 1 if the clients are compiled as thread-safe.
mysql_use_result()Initiates a row-by-row result set retrieval.
mysql_warning_count()Returns the warning count for the previous SQL statement.

Application programs should use this general outline for interacting with MySQL:

  1. Initialize the MySQL library by calling mysql_library_init(). The library can be either the mysqlclient C client library or the mysqld embedded server library, depending on whether the application was linked with the -libmysqlclient or -libmysqld flag.

  2. Initialize a connection handler by calling mysql_init() and connect to the server by calling mysql_real_connect().

  3. Issue SQL statements and process their results. (The following discussion provides more information about how to do this.)

  4. Close the connection to the MySQL server by calling mysql_close().

  5. End use of the MySQL library by calling mysql_library_end().

The purpose of calling mysql_library_init() and mysql_library_end() is to provide proper initialization and finalization of the MySQL library. For applications that are linked with the client library, they provide improved memory management. If you don't call mysql_library_end(), a block of memory remains allocated. (This does not increase the amount of memory used by the application, but some memory leak detectors will complain about it.) For applications that are linked with the embedded server, these calls start and stop the server.

mysql_library_init() and mysql_library_end() are actually #define symbols that make them equivalent to mysql_server_init() and mysql_server_end(), but the names more clearly indicate that they should be called when beginning and ending use of a MySQL library no matter whether the application uses the mysqlclient or mysqld library. For older versions of MySQL, you can call mysql_server_init() and mysql_server_end() instead.

In a non-multi-threaded environment, the call to mysql_library_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, a race condition is possible if mysql_library_init() is invoked by mysql_init() in a multi-threaded environment: mysql_library_init() is not thread-safe, so it should be called prior to any other client library call.

To connect to the server, call mysql_init() to initialize a connection handler, then call mysql_real_connect() with that handler (along with other information such as the hostname, username, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1 in versions of the API older than 5.0.3, or 0 in newer versions. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. As of MySQL 5.0.13, you can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior. When you are done with the connection, call mysql_close() to terminate it.

While a connection is active, the client may send SQL statements to the server using mysql_query() or mysql_real_query(). The difference between the two is that mysql_query() expects the query to be specified as a null-terminated string whereas mysql_real_query() expects a counted string. If the string contains binary data (which may include null bytes), you must use mysql_real_query().

For each non-SELECT query (for example, INSERT, UPDATE, DELETE), you can find out how many rows were changed (affected) by calling mysql_affected_rows().

For SELECT queries, you retrieve the selected rows as a result set. (Note that some statements are SELECT-like in that they return rows. These include SHOW, DESCRIBE, and EXPLAIN. They should be treated the same way as SELECT statements.)

There are two ways for a client to process result sets. One way is to retrieve the entire result set all at once by calling mysql_store_result(). This function acquires from the server all the rows returned by the query and stores them in the client. The second way is for the client to initiate a row-by-row result set retrieval by calling mysql_use_result(). This function initializes the retrieval, but does not actually get any rows from the server.

In both cases, you access rows by calling mysql_fetch_row(). With mysql_store_result(), mysql_fetch_row() accesses rows that have previously been fetched from the server. With mysql_use_result(), mysql_fetch_row() actually retrieves the row from the server. Information about the size of the data in each row is available by calling mysql_fetch_lengths().

After you are done with a result set, call mysql_free_result() to free the memory used for it.

The two retrieval mechanisms are complementary. Client programs should choose the approach that is most appropriate for their requirements. In practice, clients tend to use mysql_store_result() more commonly.

An advantage of mysql_store_result() is that because the rows have all been fetched to the client, you not only can access rows sequentially, you can move back and forth in the result set using mysql_data_seek() or mysql_row_seek() to change the current row position within the result set. You can also find out how many rows there are by calling mysql_num_rows(). On the other hand, the memory requirements for mysql_store_result() may be very high for large result sets and you are more likely to encounter out-of-memory conditions.

An advantage of mysql_use_result() is that the client requires less memory for the result set because it maintains only one row at a time (and because there is less allocation overhead, mysql_use_result() can be faster). Disadvantages are that you must process each row quickly to avoid tying up the server, you don't have random access to rows within the result set (you can only access rows sequentially), and you don't know how many rows are in the result set until you have retrieved them all. Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for.

The API makes it possible for clients to respond appropriately to statements (retrieving rows only as necessary) without knowing whether the statement is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the statement was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the statement returned no data (indicating that it was an INSERT, UPDATE, DELETE, and so forth), and was not expected to return rows. If mysql_field_count() is non-zero, the statement should have returned rows, but didn't. This indicates that the statement was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.

Both mysql_store_result() and mysql_use_result() allow you to obtain information about the fields that make up the result set (the number of fields, their names and types, and so forth). You can access field information sequentially within the row by calling mysql_fetch_field() repeatedly, or by field number within the row by calling mysql_fetch_field_direct(). The current field cursor position may be changed by calling mysql_field_seek(). Setting the field cursor affects subsequent calls to mysql_fetch_field(). You can also get information for fields all at once by calling mysql_fetch_fields().

For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, allowing you to determine when an error occurred and what it was.

24.2.3. C API Function Descriptions

24.2.3.1. mysql_affected_rows()
24.2.3.2. mysql_autocommit()
24.2.3.3. mysql_change_user()
24.2.3.4. mysql_character_set_name()
24.2.3.5. mysql_close()
24.2.3.6. mysql_commit()
24.2.3.7. mysql_connect()
24.2.3.8. mysql_create_db()
24.2.3.9. mysql_data_seek()
24.2.3.10. mysql_debug()
24.2.3.11. mysql_drop_db()
24.2.3.12. mysql_dump_debug_info()
24.2.3.13. mysql_eof()
24.2.3.14. mysql_errno()
24.2.3.15. mysql_error()
24.2.3.16. mysql_escape_string()
24.2.3.17. mysql_fetch_field()
24.2.3.18. mysql_fetch_field_direct()
24.2.3.19. mysql_fetch_fields()
24.2.3.20. mysql_fetch_lengths()
24.2.3.21. mysql_fetch_row()
24.2.3.22. mysql_field_count()
24.2.3.23. mysql_field_seek()
24.2.3.24. mysql_field_tell()
24.2.3.25. mysql_free_result()
24.2.3.26. mysql_get_character_set_info()
24.2.3.27. mysql_get_client_info()
24.2.3.28. mysql_get_client_version()
24.2.3.29. mysql_get_host_info()
24.2.3.30. mysql_get_proto_info()
24.2.3.31. mysql_get_server_info()
24.2.3.32. mysql_get_server_version()
24.2.3.33. mysql_get_ssl_cipher()
24.2.3.34. mysql_hex_string()
24.2.3.35. mysql_info()
24.2.3.36. mysql_init()
24.2.3.37. mysql_insert_id()
24.2.3.38. mysql_kill()
24.2.3.39. mysql_library_end()
24.2.3.40. mysql_library_init()
24.2.3.41. mysql_list_dbs()
24.2.3.42. mysql_list_fields()
24.2.3.43. mysql_list_processes()
24.2.3.44. mysql_list_tables()
24.2.3.45. mysql_more_results()
24.2.3.46. mysql_next_result()
24.2.3.47. mysql_num_fields()
24.2.3.48. mysql_num_rows()
24.2.3.49. mysql_options()
24.2.3.50. mysql_ping()
24.2.3.51. mysql_query()
24.2.3.52. mysql_real_connect()
24.2.3.53. mysql_real_escape_string()
24.2.3.54. mysql_real_query()
24.2.3.55. mysql_refresh()
24.2.3.56. mysql_reload()
24.2.3.57. mysql_rollback()
24.2.3.58. mysql_row_seek()
24.2.3.59. mysql_row_tell()
24.2.3.60. mysql_select_db()
24.2.3.61. mysql_set_character_set()
24.2.3.62. mysql_set_local_infile_default()
24.2.3.63. mysql_set_local_infile_handler()
24.2.3.64. mysql_set_server_option()
24.2.3.65. mysql_shutdown()
24.2.3.66. mysql_sqlstate()
24.2.3.67. mysql_ssl_set()
24.2.3.68. mysql_stat()
24.2.3.69. mysql_store_result()
24.2.3.70. mysql_thread_id()
24.2.3.71. mysql_use_result()
24.2.3.72. mysql_warning_count()

In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value.

Functions that return a value generally return a pointer or an integer. Unless specified otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or non-zero to indicate an error. Note that “non-zero” means just that. Unless the function description says otherwise, do not test against a value other than zero:

if (result)                   /* correct */
    ... error ...

if (result < 0)               /* incorrect */
    ... error ...

if (result == -1)             /* incorrect */
    ... error ...

When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can find out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().

24.2.3.1. mysql_affected_rows()

my_ulonglong mysql_affected_rows(MYSQL *mysql)

Description

Returns the number of rows changed by the last UPDATE, deleted by the last DELETE or inserted by the last INSERT statement. May be called immediately after mysql_query() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_affected_rows() works like mysql_num_rows().

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_affected_rows() was called prior to calling mysql_store_result(). Because mysql_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

Errors

None.

Example

mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%ld products updated",(long) mysql_affected_rows(&mysql));

If you specify the flag CLIENT_FOUND_ROWS when connecting to mysqld, mysql_affected_rows() returns the number of rows matched by the WHERE statement for UPDATE statements. Otherwise, it returns the number of rows actually changed.

Note that when you use a REPLACE command, mysql_affected_rows() returns 2 if the new row replaced an old row, because in this case, one row was inserted after the duplicate was deleted.

If you use INSERT ... ON DUPLICATE KEY UPDATE to insert a row, mysql_affected_rows() returns 1 if the row is inserted as a new row and 2 if an existing row is updated.

24.2.3.2. mysql_autocommit()

my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)

Description

Sets autocommit mode on if mode is 1, off if mode is 0.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

24.2.3.3. mysql_change_user()

my_bool mysql_change_user(MYSQL *mysql, const char *user, const char *password, const char *db)

Description

Changes the user and causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

mysql_change_user() fails if the connected user cannot be authenticated or doesn't have permission to use the database. In this case, the user and database are not changed

The db parameter may be set to NULL if you don't want to have a default database.

This command always performs a ROLLBACK of any active transactions, closes all temporary tables, unlocks all locked tables and resets the state as if one had done a new connect. Session system variables are reset to the values of the corresponding global system variables and HANDLER variables are closed. These effects occur even if the user didn't change.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

The same that you can get from mysql_real_connect().

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

  • ER_UNKNOWN_COM_ERROR

    The MySQL server doesn't implement this command (probably an old server).

  • ER_ACCESS_DENIED_ERROR

    The user or password was wrong.

  • ER_BAD_DB_ERROR

    The database didn't exist.

  • ER_DBACCESS_DENIED_ERROR

    The user did not have access rights to the database.

  • ER_WRONG_DB_NAME

    The database name was too long.

Example

if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
   fprintf(stderr, "Failed to change user.  Error: %s\n",
           mysql_error(&mysql));
}

24.2.3.4. mysql_character_set_name()

const char *mysql_character_set_name(MYSQL *mysql)

Description

Returns the default character set for the current connection.

Return Values

The default character set

Errors

None.

24.2.3.5. mysql_close()

void mysql_close(MYSQL *mysql)

Description

Closes a previously opened connection. mysql_close() also deallocates the connection handle pointed to by mysql if the handle was allocated automatically by mysql_init() or mysql_connect().

Return Values

None.

Errors

None.

24.2.3.6. mysql_commit()

my_bool mysql_commit(MYSQL *mysql)

Description

Commits the current transaction.

The action of this function is subject to the value of the completion_type system variable. In particular, if the value of completion_type is 2, the server performs a release after terminating a transaction and closes the client connection. The client program should call mysql_close() to close the connection from the client side.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

24.2.3.7. mysql_connect()

MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)

Description

This function is deprecated. It is preferable to use mysql_real_connect() instead.

mysql_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().

The meanings of the parameters are the same as for the corresponding parameters for mysql_real_connect() with the difference that the connection parameter may be NULL. In this case, the C API allocates memory for the connection structure automatically and frees it when you call mysql_close(). The disadvantage of this approach is that you can't retrieve an error message if the connection fails. (To get error information from mysql_errno() or mysql_error(), you must provide a valid MYSQL pointer.)

Return Values

Same as for mysql_real_connect().

Errors

Same as for mysql_real_connect().

24.2.3.8. mysql_create_db()

int mysql_create_db(MYSQL *mysql, const char *db)

Description

Creates the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL CREATE DATABASE statement instead.

Return Values

Zero if the database was created successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

if(mysql_create_db(&mysql, "my_database"))
{
   fprintf(stderr, "Failed to create new database.  Error: %s\n",
           mysql_error(&mysql));
}

24.2.3.9. mysql_data_seek()

void mysql_data_seek(MYSQL_RES *result, my_ulonglong offset)

Description

Seeks to an arbitrary row in a query result set. The offset value is a row number and should be in the range from 0 to mysql_num_rows(result)-1.

This function requires that the result set structure contains the entire result of the query, so mysql_data_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

None.

Errors

None.

24.2.3.10. mysql_debug()

void mysql_debug(const char *debug)

Description

Does a DBUG_PUSH with the given string. mysql_debug() uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. See Section F.1, “Debugging a MySQL Server”, and Section F.2, “Debugging a MySQL Client”.

Return Values

None.

Errors

None.

Example

The call shown here causes the client library to generate a trace file in /tmp/client.trace on the client machine:

mysql_debug("d:t:O,/tmp/client.trace");

24.2.3.11. mysql_drop_db()

int mysql_drop_db(MYSQL *mysql, const char *db)

Description

Drops the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL DROP DATABASE statement instead.

Return Values

Zero if the database was dropped successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

if(mysql_drop_db(&mysql, "my_database"))
  fprintf(stderr, "Failed to drop the database: Error: %s\n",
          mysql_error(&mysql));

24.2.3.12. mysql_dump_debug_info()

int mysql_dump_debug_info(MYSQL *mysql)

Description

Instructs the server to write some debug information to the log. For this to work, the connected user must have the SUPER privilege.

Return Values

Zero if the command was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.13. mysql_eof()

my_bool mysql_eof(MYSQL_RES *result)

Description

This function is deprecated. mysql_errno() or mysql_error() may be used instead.

mysql_eof() determines whether the last row of a result set has been read.

If you acquire a result set from a successful call to mysql_store_result(), the client receives the entire set in one operation. In this case, a NULL return from mysql_fetch_row() always means the end of the result set has been reached and it is unnecessary to call mysql_eof(). When used with mysql_store_result(), mysql_eof() always returns true.

On the other hand, if you use mysql_use_result() to initiate a result set retrieval, the rows of the set are obtained from the server one by one as you call mysql_fetch_row() repeatedly. Because an error may occur on the connection during this process, a NULL return value from mysql_fetch_row() does not necessarily mean the end of the result set was reached normally. In this case, you can use mysql_eof() to determine what happened. mysql_eof() returns a non-zero value if the end of the result set was reached and zero if an error occurred.

Historically, mysql_eof() predates the standard MySQL error functions mysql_errno() and mysql_error(). Because those error functions provide the same information, their use is preferred over mysql_eof(), which is deprecated. (In fact, they provide more information, because mysql_eof() returns only a boolean value whereas the error functions indicate a reason for the error when one occurs.)

Return Values

Zero if no error occurred. Non-zero if the end of the result set has been reached.

Errors

None.

Example

The following example shows how you might use mysql_eof():

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(!mysql_eof(result))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

However, you can achieve the same effect with the standard MySQL error functions:

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(mysql_errno(&mysql))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

24.2.3.14. mysql_errno()

unsigned int mysql_errno(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_errno() returns the error code for the most recently invoked API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix C, Error Codes and Messages.

Note that some functions like mysql_fetch_row() don't set mysql_errno() if they succeed.

A rule of thumb is that all functions that have to ask the server for information reset mysql_errno() if they succeed.

MySQL-specific error numbers returned by mysql_errno() differ from SQLSTATE values returned by mysql_sqlstate(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist

Return Values

An error code value for the last mysql_xxx() call, if it failed. zero means no error occurred.

Errors

None.

24.2.3.15. mysql_error()

const char *mysql_error(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_error() returns a null-terminated string containing the error message for the most recently invoked API function that failed. If a function didn't fail, the return value of mysql_error() may be the previous error or an empty string to indicate no error.

A rule of thumb is that all functions that have to ask the server for information reset mysql_error() if they succeed.

For functions that reset mysql_errno(), the following two tests are equivalent:

if(*mysql_errno(&mysql))
{
  // an error occurred
}

if(mysql_error(&mysql)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently, you can choose error messages in several different languages. See Section 5.11.2, “Setting the Error Message Language”.

Return Values

A null-terminated character string that describes the error. An empty string if no error occurred.

Errors

None.

24.2.3.16. mysql_escape_string()

You should use mysql_real_escape_string() instead!

This function is identical to mysql_real_escape_string() except that mysql_real_escape_string() takes a connection handler as its first argument and escapes the string according to the current character set. mysql_escape_string() does not take a connection argument and does not respect the current character set.

24.2.3.17. mysql_fetch_field()

MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)

Description

Returns the definition of one column of a result set as a MYSQL_FIELD structure. Call this function repeatedly to retrieve information about all columns in the result set. mysql_fetch_field() returns NULL when no more fields are left.

mysql_fetch_field() is reset to return information about the first field each time you execute a new SELECT query. The field returned by mysql_fetch_field() is also affected by calls to mysql_field_seek().

If you've called mysql_query() to perform a SELECT on a table but have not called mysql_store_result(), MySQL returns the default blob length (8KB) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8KB size is chosen because MySQL doesn't know the maximum length for the BLOB. This should be made configurable sometime.) Once you've retrieved the result set, field->max_length contains the length of the largest value for this column in the specific query.

Return Values

The MYSQL_FIELD structure for the current column. NULL if no columns are left.

Errors

None.

Example

MYSQL_FIELD *field;

while((field = mysql_fetch_field(result)))
{
    printf("field name %s\n", field->name);
}

24.2.3.18. mysql_fetch_field_direct()

MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)

Description

Given a field number fieldnr for a column within a result set, returns that column's field definition as a MYSQL_FIELD structure. You may use this function to retrieve the definition for an arbitrary column. The value of fieldnr should be in the range from 0 to mysql_num_fields(result)-1.

Return Values

The MYSQL_FIELD structure for the specified column.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;

num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
    field = mysql_fetch_field_direct(result, i);
    printf("Field %u is %s\n", i, field->name);
}

24.2.3.19. mysql_fetch_fields()

MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)

Description

Returns an array of all MYSQL_FIELD structures for a result set. Each structure provides the field definition for one column of the result set.

Return Values

An array of MYSQL_FIELD structures for all columns of a result set.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;

num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
   printf("Field %u is %s\n", i, fields[i].name);
}

24.2.3.20. mysql_fetch_lengths()

unsigned long *mysql_fetch_lengths(MYSQL_RES *result)

Description

Returns the lengths of the columns of the current row within a result set. If you plan to copy field values, this length information is also useful for optimization, because you can avoid calling strlen(). In addition, if the result set contains binary data, you must use this function to determine the size of the data, because strlen() returns incorrect results for any field containing null characters.

The length for empty columns and for columns containing NULL values is zero. To see how to distinguish these two cases, see the description for mysql_fetch_row().

Return Values

An array of unsigned long integers representing the size of each column (not including any terminating null characters). NULL if an error occurred.

Errors

mysql_fetch_lengths() is valid only for the current row of the result set. It returns NULL if you call it before calling mysql_fetch_row() or after retrieving all rows in the result.

Example

MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;

row = mysql_fetch_row(result);
if (row)
{
    num_fields = mysql_num_fields(result);
    lengths = mysql_fetch_lengths(result);
    for(i = 0; i < num_fields; i++)
    {
         printf("Column %u is %lu bytes in length.\n", 
                i, lengths[i]);
    }
}

24.2.3.21. mysql_fetch_row()

MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)

Description

Retrieves the next row of a result set. When used after mysql_store_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve. When used after mysql_use_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve or if an error occurred.

The number of values in the row is given by mysql_num_fields(result). If row holds the return value from a call to mysql_fetch_row(), pointers to the values are accessed as row[0] to row[mysql_num_fields(result)-1]. NULL values in the row are indicated by NULL pointers.

The lengths of the field values in the row may be obtained by calling mysql_fetch_lengths(). Empty fields and fields containing NULL both have length 0; you can distinguish these by checking the pointer for the field value. If the pointer is NULL, the field is NULL; otherwise, the field is empty.

Return Values

A MYSQL_ROW structure for the next row. NULL if there are no more rows to retrieve or if an error occurred.

Errors

Note that error is not reset between calls to mysql_fetch_row()

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;

num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
   unsigned long *lengths;
   lengths = mysql_fetch_lengths(result);
   for(i = 0; i < num_fields; i++)
   {
       printf("[%.*s] ", (int) lengths[i], 
              row[i] ? row[i] : "NULL");
   }
   printf("\n");
}

24.2.3.22. mysql_field_count()

unsigned int mysql_field_count(MYSQL *mysql)

Description

Returns the number of columns for the most recent query on the connection.

The normal use of this function is when mysql_store_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 24.2.13.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if(mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
        else // mysql_store_result() should have returned data
        {
            fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
    }
}

An alternative is to replace the mysql_field_count(&mysql) call with mysql_errno(&mysql). In this case, you are checking directly for an error from mysql_store_result() rather than inferring from the value of mysql_field_count() whether the statement was a SELECT.

24.2.3.23. mysql_field_seek()

MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)

Description

Sets the field cursor to the given offset. The next call to mysql_fetch_field() retrieves the field definition of the column associated with that offset.

To seek to the beginning of a row, pass an offset value of zero.

Return Values

The previous value of the field cursor.

Errors

None.

24.2.3.24. mysql_field_tell()

MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)

Description

Returns the position of the field cursor used for the last mysql_fetch_field(). This value can be used as an argument to mysql_field_seek().

Return Values

The current offset of the field cursor.

Errors

None.

24.2.3.25. mysql_free_result()

void mysql_free_result(MYSQL_RES *result)

Description

Frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), and so forth. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().

Do not attempt to access a result set after freeing it.

Return Values

None.

Errors

None.

24.2.3.26. mysql_get_character_set_info()

void mysql_get_character_set_info(MYSQL *mysql, MY_CHARSET_INFO *cs)

Description

This function provides information about the default client character set. The default character set may be changed with the mysql_set_character_set() function.

This function was added in MySQL 5.0.10.

Example

if (!mysql_set_character_set(&mysql, "utf8"))
{
    MY_CHARSET_INFO cs;
    mysql_get_character_set_info(&mysql, &cs);
    printf("character set information:\n");
    printf("character set name: %s\n", cs.name);
    printf("collation name: %s\n", cs.csname);
    printf("comment: %s\n", cs.comment);
    printf("directory: %s\n", cs.dir);
    printf("multi byte character min. length: %d\n", cs.mbminlen);
    printf("multi byte character max. length: %d\n", cs.mbmaxlen);
}

24.2.3.27. mysql_get_client_info()

const char *mysql_get_client_info(void)

Description

Returns a string that represents the client library version.

Return Values

A character string that represents the MySQL client library version.

Errors

None.

24.2.3.28. mysql_get_client_version()

unsigned long mysql_get_client_version(void)

Description

Returns an integer that represents the client library version. The value has the format XYYZZ where X is the major version, YY is the release level, and ZZ is the version number within the release level. For example, a value of 40102 represents a client library version of 4.1.2.

Return Values

An integer that represents the MySQL client library version.

Errors

None.

24.2.3.29. mysql_get_host_info()

const char *mysql_get_host_info(MYSQL *mysql)

Description

Returns a string describing the type of connection in use, including the server hostname.

Return Values

A character string representing the server hostname and the connection type.

Errors

None.

24.2.3.30. mysql_get_proto_info()

unsigned int mysql_get_proto_info(MYSQL *mysql)

Description

Returns the protocol version used by current connection.

Return Values

An unsigned integer representing the protocol version used by the current connection.

Errors

None.

24.2.3.31. mysql_get_server_info()

const char *mysql_get_server_info(MYSQL *mysql)

Description

Returns a string that represents the server version number.

Return Values

A character string that represents the server version number.

Errors

None.

24.2.3.32. mysql_get_server_version()

unsigned long mysql_get_server_version(MYSQL *mysql)

Description

Returns the version number of the server as an integer.

Return Values

A number that represents the MySQL server version in this format:

major_version*10000 + minor_version *100 + sub_version

For example, 5.1.5 is returned as 50105.

This function is useful in client programs for quickly determining whether some version-specific server capability exists.

Errors

None.

24.2.3.33. mysql_get_ssl_cipher()

const char *mysql_get_ssl_cipher(MYSQL *mysql)

Description

mysql_get_ssl_cipher() returns the SSL cipher used for the given connection to the server. mysql is the connection handler returned from mysql_init().

This function was added in MySQL 5.1.9.

Return Values

A string naming the SSL cipher used for the connection, or NULL if no cipher is being used.

24.2.3.34. mysql_hex_string()

unsigned long mysql_hex_string(char *to, const char *from, unsigned long length)

Description

This function is used to create a legal SQL string that you can use in an SQL statement. See Section 9.1.1, “Strings”.

The string in from is encoded to hexadecimal format, with each character encoded as two hexadecimal digits. The result is placed in to and a terminating null byte is appended.

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. When mysql_hex_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.

The return value can be placed into an SQL statement using either 0xvalue or X'value' format. However, the return value does not include the 0x or X'...'. The caller must supply whichever of those is desired.

Example

char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
end = strmov(end,"0x");
end += mysql_hex_string(end,"What's this",11);
end = strmov(end,",0x");
end += mysql_hex_string(end,"binary data: \0\r\n",16);
*end++ = ')';

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the value placed into to, not including the terminating null character.

Errors

None.

24.2.3.35. mysql_info()

const char *mysql_info(MYSQL *mysql)

Description

Retrieves a string providing information about the most recently executed query, but only for the statements listed here. For other statements, mysql_info() returns NULL. The format of the string varies depending on the type of query, as described here. The numbers are illustrative only; the string contains values appropriate for the query.

  • INSERT INTO ... SELECT ...

    String format: Records: 100 Duplicates: 0 Warnings: 0

  • INSERT INTO ... VALUES (...),(...),(...)...

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • LOAD DATA INFILE ...

    String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0

  • ALTER TABLE

    String format: Records: 3 Duplicates: 0 Warnings: 0

  • UPDATE

    String format: Rows matched: 40 Changed: 40 Warnings: 0

Note that mysql_info() returns a non-NULL value for INSERT ... VALUES only for the multiple-row form of the statement (that is, only if multiple value lists are specified).

Return Values

A character string representing additional information about the most recently executed query. NULL if no information is available for the query.

Errors

None.

24.2.3.36. mysql_init()

MYSQL *mysql_init(MYSQL *mysql)

Description

Allocates or initializes a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initializes, and returns a new object. Otherwise, the object is initialized and the address of the object is returned. If mysql_init() allocates a new object, it is freed when mysql_close() is called to close the connection.

Return Values

An initialized MYSQL* handle. NULL if there was insufficient memory to allocate a new object.

Errors

In case of insufficient memory, NULL is returned.

24.2.3.37. mysql_insert_id()

my_ulonglong mysql_insert_id(MYSQL *mysql)

Description

Returns the value generated for an AUTO_INCREMENT column by the previous INSERT statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field.

The return value of mysql_insert_id() is always zero unless explicitly updated under one of the following conditions:

  • INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit non-special value.

  • In the case of a multiple-row INSERT statement, the return value of mysql_insert_id() depends on the MySQL server version.

    In MySQL 5.1.12 and later, mysql_insert_id() returns the the first automatically generated AUTO_INCREMENT value that was successfully inserted. In MySQL 5.1.11 and earlier, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value, regardless of whether the insertion of that value was successful.

    If no rows are successfully inserted, then mysql_insert_id() returns 0.

  • Starting in MySQL 5.1.12, if an INSERT ... SELECT statement is executed, and no automatically generated value is successfully inserted, then mysql_insert_id() returns the id of the last inserted row.

  • Starting in MySQL 5.1.12, if an INSERT ... SELECT statement uses LAST_INSERT_ID(expr), then mysql_insert_id() returns expr.

  • INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column.

  • INSERT statements that generate an AUTO_INCREMENT value by updating any column to LAST_INSERT_ID(expr).

  • The value of mysql_insert_id() is not affected by statements such as SELECT that return a result set.

  • If the previous statement returned an error, the value of mysql_insert_id() is undefined.

For 5.1.12 and later, the return value of mysql_insert_id() can be simplifiedto the following sequence:

  1. If there is an a auto increment columne, and an automatically generated value was successfully inserted, return the value of the first such value.

  2. If there was a LAST_INSERT_ID(EXPR) in the statement, return EXPR, even if there was an auto increment column in the affected table.

  3. If there is an auto increment column in the table, and there were some explicit values for this column that were successfully inserted into the table, then return the last of the explicit values.

Note

mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.

The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.

See Section 12.10.3, “Information Functions”.

Also note that the value of the SQL LAST_INSERT_ID() function will contain the the value of the first automatically generated value that was successfully inserted (starting from 5.1.12) or the firust automatically generated value if any rows were successfully inserted (before 5.1.12). Another difference is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific non-special value.

The reason for the difference between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide a little more exact information of what happens to the AUTO_INCREMENT column.

Return Values

Described in the preceding discussion.

Errors

None.

24.2.3.38. mysql_kill()

int mysql_kill(MYSQL *mysql, unsigned long pid)

Description

Asks the server to kill the thread specified by pid.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.39. mysql_library_end()

void mysql_library_end(void)

Description

This is a synonym for the mysql_server_end() function.

See Section 24.2.2, “C API Function Overview”, for usage information.

24.2.3.40. mysql_library_init()

int mysql_library_init(int argc, char **argv, char **groups)

Description

This is a synonym for the mysql_server_init() function. See Section 24.2.12.1, “mysql_server_init().

See Section 24.2.2, “C API Function Overview” for usage information.

24.2.3.41. mysql_list_dbs()

MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of database names on the server that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters ‘%’ or ‘_’, or may be a NULL pointer to match all databases. Calling mysql_list_dbs() is similar to executing the query SHOW databases [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.42. mysql_list_fields()

MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)

Description

Returns a result set consisting of field names in the given table that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters ‘%’ or ‘_’, or may be a NULL pointer to match all fields. Calling mysql_list_fields() is similar to executing the query SHOW COLUMNS FROM tbl_name [LIKE wild].

Note that it's recommended that you use SHOW COLUMNS FROM tbl_name instead of mysql_list_fields().

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.43. mysql_list_processes()

MYSQL_RES *mysql_list_processes(MYSQL *mysql)

Description

Returns a result set describing the current server threads. This is the same kind of information as that reported by mysqladmin processlist or a SHOW PROCESSLIST query.

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.44. mysql_list_tables()

MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of table names in the current database that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters ‘%’ or ‘_’, or may be a NULL pointer to match all tables. Calling mysql_list_tables() is similar to executing the query SHOW tables [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.45. mysql_more_results()

my_bool mysql_more_results(MYSQL *mysql)

Description

Returns true if more results exist from the currently executed query, and the application must call mysql_next_result() to fetch the results.

Return Values

TRUE (1) if more results exist. FALSE (0) if no more results exist.

In most cases, you can call mysql_next_result() instead to test whether more results exist and initiate retrieval if so.

See Section 24.2.9, “C API Handling of Multiple Statement Execution”, and Section 24.2.3.46, “mysql_next_result().

Errors

None.

24.2.3.46. mysql_next_result()

int mysql_next_result(MYSQL *mysql)

Description

If more query results exist, mysql_next_result() reads the next query results and returns the status back to application.

You must call mysql_free_result() for the preceding query if it returned a result set.

After calling mysql_next_result() the state of the connection is as if you had called mysql_real_query() or mysql_query() for the next query. This means that you can call mysql_store_result(), mysql_warning_count(), mysql_affected_rows(), and so forth.

If mysql_next_result() returns an error, no other statements are executed and there are no more results to fetch.

If your program executes stored procedures with the CALL SQL statement, you must set the CLIENT_MULTI_RESULTS flag, either explicitly, or implicitly by setting CLIENT_MULTI_STATEMENTS when you call mysql_real_connect(). This is because each CALL returns a result to indicate the call status, in addition to any results sets that might be returned by statements executed within the procedure. In addition, because CALL can return multiple results, you should process those results using a loop that calls mysql_next_result() to determine whether there are more results.

For an example that shows how to use mysql_next_result(), see Section 24.2.9, “C API Handling of Multiple Statement Execution”.

Return Values

Return ValueDescription
0Successful and there are more results
-1Successful and there are no more results
>0An error occurred

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order. For example if you didn't call mysql_use_result() for a previous result set.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.47. mysql_num_fields()

unsigned int mysql_num_fields(MYSQL_RES *result)

To pass a MYSQL* argument instead, use unsigned int mysql_field_count(MYSQL *mysql).

Description

Returns the number of columns in a result set.

Note that you can get the number of columns either from a pointer to a result set or to a connection handle. You would use the connection handle if mysql_store_result() or mysql_use_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See Section 24.2.13.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if (mysql_errno(&mysql))
        {
           fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
        else if (mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
    }
}

An alternative (if you know that your query should have returned a result set) is to replace the mysql_errno(&mysql) call with a check whether mysql_field_count(&mysql) is = 0. This happens only if something went wrong.

24.2.3.48. mysql_num_rows()

my_ulonglong mysql_num_rows(MYSQL_RES *result)

Description

Returns the number of rows in the result set.

The use of mysql_num_rows() depends on whether you use mysql_store_result() or mysql_use_result() to return the result set. If you use mysql_store_result(), mysql_num_rows() may be called immediately. If you use mysql_use_result(), mysql_num_rows() does not return the correct value until all the rows in the result set have been retrieved.

mysql_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_affected_rows().

Return Values

The number of rows in the result set.

Errors

None.

24.2.3.49. mysql_options()

int mysql_options(MYSQL *mysql, enum mysql_option option, const char *arg)

Description

Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.

mysql_options() should be called after mysql_init() and before mysql_connect() or mysql_real_connect().

The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, then arg should point to the value of the integer.

Possible option values:

OptionArgument TypeFunction
MYSQL_INIT_COMMANDchar *Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting.
MYSQL_OPT_COMPRESSNot usedUse the compressed client/server protocol.
MYSQL_OPT_CONNECT_TIMEOUTunsigned int *Connect timeout in seconds.
MYSQL_OPT_GUESS_CONNECTIONNot usedFor an application linked against libmysqld, this allows the library to guess whether to use the embedded server or a remote server. “Guess” means that if the hostname is set and is not localhost, it uses a remote server. This behavior is the default. MYSQL_OPT_USE_EMBEDDED_CONNECTION and MYSQL_OPT_USE_REMOTE_CONNECTION can be used to override it. This option is ignored for applications linked against libmysqlclient.
MYSQL_OPT_LOCAL_INFILEoptional pointer to uintIf no pointer is given or if pointer points to an unsigned int != 0 the command LOAD LOCAL INFILE is enabled.
MYSQL_OPT_NAMED_PIPENot usedUse named pipes to connect to a MySQL server on NT.
MYSQL_OPT_PROTOCOLunsigned int *Type of protocol to use. Should be one of the enum values of mysql_protocol_type defined in mysql.h.
MYSQL_OPT_READ_TIMEOUTunsigned int *Timeout for reads from server (works only for TCP/IP connections, and only for Windows prior to MySQL 5.1.12). You can this option so that a lost connection can be detected earlier than the TCP/IP Close_Wait_Timeout value of 10 minutes.
MYSQL_OPT_RECONNECTmy_bool *Enable or disable automatic reconnection to the server if the connection is found to have been lost. Reconnect has been off by default since MySQL 5.0.3; this option is new in 5.0.13 and provides a way to set reconnection behavior explicitly.
MYSQL_OPT_SET_CLIENT_IPchar *For an application linked against linked against libmysqld (with libmysqld compiled with authentication support), this means that the user is considered to have connected from the specified IP address (specified as a string) for authentication purposes. This option is ignored for applications linked against libmysqlclient.
MYSQL_OPT_SSL_VERIFY_SERVER_CERTmy_bool *Enable or disable verification of the server's Common Name value in its certificate against the hostname used when connecting to the server. The connection is rejected if there is a mismatch. This feature can be used to prevent man-in-the-middle attacks. Verification is disabled by default. Added in MySQL 5.1.11.
MYSQL_OPT_USE_EMBEDDED_CONNECTIONNot usedFor an application linked against libmysqld, this forces the use of the embedded server for the connection. This option is ignored for applications linked against libmysqlclient.
MYSQL_OPT_USE_REMOTE_CONNECTIONNot usedFor an application linked against libmysqld, this forces the use of a remote server for the connection. This option is ignored for applications linked against libmysqlclient.
MYSQL_OPT_USE_RESULTNot usedThis option is unused.
MYSQL_OPT_WRITE_TIMEOUTunsigned int *Timeout for writes to server (works currently only on Windows on TCP/IP connections).
MYSQL_READ_DEFAULT_FILEchar *Read options from the named option file instead of from my.cnf.
MYSQL_READ_DEFAULT_GROUPchar *Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE.
MYSQL_REPORT_DATA_TRUNCATIONmy_bool *Enable or disable reporting of data truncation errors for prepared statements via MYSQL_BIND.error. (Default: enabled.)
MYSQL_SECURE_AUTHmy_bool*Whether to connect to a server that does not support the password hashing used in MySQL 4.1.1 and later.
MYSQL_SET_CHARSET_DIRchar*The pathname to the directory that contains character set definition files.
MYSQL_SET_CHARSET_NAMEchar*The name of the character set to use as the default character set.
MYSQL_SHARED_MEMORY_BASE_NAMEchar*Named of shared-memory object for communication to server. Should be same as the option --shared-memory-base-name used for the mysqld server you want to connect to.

Note that the client group is always read if you use MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.

The specified group in the option file may contain the following options:

OptionDescription
connect-timeoutConnect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server.
compressUse the compressed client/server protocol.
databaseConnect to this database if no database was specified in the connect command.
debugDebug options.
disable-local-infileDisable use of LOAD DATA LOCAL.
hostDefault hostname.
init-commandCommand to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting.
interactive-timeoutSame as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See Section 24.2.3.52, “mysql_real_connect().
local-infile[=(0|1)]If no argument or argument != 0 then enable use of LOAD DATA LOCAL.
max_allowed_packetMax size of packet client can read from server.
multi-resultsAllow multiple result sets from multiple-statement executions or stored procedures.
multi-statementsAllow the client to send multiple statements in a single string (separated by ‘;’).
passwordDefault password.
pipeUse named pipes to connect to a MySQL server on NT.
protocol={TCP|SOCKET|PIPE|MEMORY}The protocol to use when connecting to the server.
portDefault port number.
return-found-rowsTell mysql_info() to return found rows instead of updated rows when using UPDATE.
shared-memory-base-name=nameShared-memory name to use to connect to server (default is "MYSQL").
socketDefault socket file.
userDefault user.

Note that timeout has been replaced by connect-timeout, but timeout is still supported in MySQL 5.1.14-beta for backward compatibility.

For more information about option files, see Section 4.3.2, “Using Option Files”.

Return Values

Zero for success. Non-zero if you used an unknown option.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

This code requests the client to use the compressed client/server protocol and read the additional options from the odbc section in the my.cnf file.

24.2.3.50. mysql_ping()

int mysql_ping(MYSQL *mysql)

Description

Checks whether the connection to the server is working. If the connection has gone down, an automatic reconnection is attempted.

This function can be used by clients that remain idle for a long while, to check whether the server has closed the connection and reconnect if necessary.

Return Values

Zero if the connection to the server is alive. Non-zero if an error occurred. A non-zero return does not indicate whether the MySQL server itself is down; the connection might be broken for other reasons such as network problems.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.51. mysql_query()

int mysql_query(MYSQL *mysql, const char *query)

Description

Executes the SQL query pointed to by the null-terminated string query. Normally, the string must consist of a single SQL statement and you should not add a terminating semicolon (‘;’) or \g to the statement. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 24.2.9, “C API Handling of Multiple Statement Execution”.

mysql_query() cannot be used for queries that contain binary data; you should use mysql_real_query() instead. (Binary data may contain the ‘\0’ character, which mysql_query() interprets as the end of the query string.)

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 24.2.3.22, “mysql_field_count().

Return Values

Zero if the query was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.52. mysql_real_connect()

MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)

Description

mysql_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any other API functions that require a valid MYSQL connection handle structure.

The parameters are specified as follows:

  • The first parameter should be the address of an existing MYSQL structure. Before calling mysql_real_connect() you must call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See Section 24.2.3.49, “mysql_options().

  • The value of host may be either a hostname or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed: For Windows, the client connects using a shared-memory connection, if the server has shared-memory connections enabled. Otherwise, TCP/IP is used. For Unix, the client connects using a Unix socket file. For local connections, you can also influence the type of connection to use with the MYSQL_OPT_PROTOCOL or MYSQL_OPT_NAMED_PIPE options to mysql_options(). The type of connection must be supported by the server. For a host value of "." on Windows, the client connects using a named pipe, if the server has named-pipe connections enabled. If named-pipe connections are not enabled, an error occurs.

  • The user parameter contains the user's MySQL login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current username must be specified explicitly. See the MyODBC section of Chapter 25, Connectors.

  • The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field are checked for a match. This allows the database administrator to set up the MySQL privilege system in such a way that users get different privileges depending on whether they have specified a password.

    Note: Do not attempt to encrypt the password before calling mysql_real_connect(); password encryption is handled automatically by the client API.

  • db is the database name. If db is not NULL, the connection sets the default database to this value.

  • If port is not 0, the value is used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection.

  • If unix_socket is not NULL, the string specifies the socket or named pipe that should be used. Note that the host parameter determines the type of the connection.

  • The value of client_flag is usually 0, but can be set to a combination of the following flags to enable certain features:

    Flag NameFlag Description
    CLIENT_COMPRESSUse compression protocol.
    CLIENT_FOUND_ROWSReturn the number of found (matched) rows, not the number of changed rows.
    CLIENT_IGNORE_SPACEAllow spaces after function names. Makes all functions names reserved words.
    CLIENT_INTERACTIVEAllow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client's session wait_timeout variable is set to the value of the session interactive_timeout variable.
    CLIENT_LOCAL_FILESEnable LOAD DATA LOCAL handling.
    CLIENT_MULTI_STATEMENTSTell the server that the client may send multiple statements in a single string (separated by ‘;’). If this flag is not set, multiple-statement execution is disabled. See the note following this table for more information about this flag.
    CLIENT_MULTI_RESULTSTell the server that the client can handle multiple result sets from multiple-statement executions or stored procedures. This is automatically set if CLIENT_MULTI_STATEMENTS is set. See the note following this table for more information about this flag.
    CLIENT_NO_SCHEMADon't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.
    CLIENT_ODBCThe client is an ODBC client. This changes mysqld to be more ODBC-friendly.
    CLIENT_SSLUse SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library. Instead, use mysql_ssl_set() before calling mysql_real_connect().

If your program executes stored procedures with the CALL SQL statement, you must set the CLIENT_MULTI_RESULTS flag, either explicitly, or implicitly by setting CLIENT_MULTI_STATEMENTS when you call mysql_real_connect(). This is because each CALL returns a result to indicate the call status, in addition to any results sets that might be returned by statements executed within the procedure.

If you enable CLIENT_MULTI_STATEMENTS or CLIENT_MULTI_RESULTS, you should process the result for every call to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 24.2.9, “C API Handling of Multiple Statement Execution”.

For some parameters, it is possible to have the value taken from an option file rather than from an explicit value in the mysql_real_connect() call. To do this, call mysql_options() with the MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP option before calling mysql_real_connect(). Then, in the mysql_real_connect() call, specify the “no-value” value for each parameter to be read from an option file:

  • For host, specify a value of NULL or the empty string ("").

  • For user, specify a value of NULL or the empty string.

  • For passwd, specify a value of NULL. (For the password, a value of the empty string in the mysql_real_connect() call cannot be overridden in an option file, because the empty string indicates explicitly that the MySQL account must have an empty password.)

  • For db, specify a value of NULL or the empty string.

  • For port, specify a value of 0.

  • For unix_socket, specify a value of NULL.

If no value is found in an option file for a parameter, its default value is used as indicated in the descriptions given earlier in this section.

Return Values

A MYSQL* connection handle if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.

Errors

  • CR_CONN_HOST_ERROR

    Failed to connect to the MySQL server.

  • CR_CONNECTION_ERROR

    Failed to connect to the local MySQL server.

  • CR_IPSOCK_ERROR

    Failed to create an IP socket.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SOCKET_CREATE_ERROR

    Failed to create a Unix socket.

  • CR_UNKNOWN_HOST

    Failed to find the IP address for the hostname.

  • CR_VERSION_ERROR

    A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the --old-protocol option.

  • CR_NAMEDPIPEOPEN_ERROR

    Failed to create a named pipe on Windows.

  • CR_NAMEDPIPEWAIT_ERROR

    Failed to wait for a named pipe on Windows.

  • CR_NAMEDPIPESETSTATE_ERROR

    Failed to get a pipe handler on Windows.

  • CR_SERVER_LOST

    If connect_timeout > 0 and it took longer than connect_timeout seconds to connect to the server or if the server died while executing the init-command.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

By using mysql_options() the MySQL library reads the [client] and [your_prog_name] sections in the my.cnf file which ensures that your program works, even if someone has set up MySQL in some non-standard way.

Note that upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1 in versions of the API older than 5.0.3, or 0 in newer versions. A value of 1 for this flag indicates that if a statement cannot be performed because of a lost connection, to try reconnecting to the server before giving up. As of MySQL 5.0.13, you can use the MYSQL_OPT_RECONNECT option to mysql_options() to control reconnection behavior.

24.2.3.53. mysql_real_escape_string()

unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)

Note that mysql must be a valid, open connection. This is needed because the escaping depends on the character set in use by the server.

Description

This function is used to create a legal SQL string that you can use in an SQL statement. See Section 9.1.1, “Strings”.

The string in from is encoded to an escaped SQL string, taking into account the current character set of the connection. The result is placed in to and a terminating null byte is appended. Characters encoded are NUL (ASCII 0), ‘\n’, ‘\r’, ‘\’, ‘'’, ‘"’, and Control-Z (see Section 9.1, “Literal Values”). (Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. This function quotes the other characters to make them easier to read in log files.)

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and you need room for the terminating null byte.) When mysql_real_escape_string() returns, the contents of to is a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.

If you need to change the character set of the connection, you should use the mysql_set_character_set() function rather than executing a SET NAMES (or SET CHARACTER SET) statement. mysql_set_character_set() works like SET NAMES but also affects the character set used by mysql_real_escape_string(), which SET NAMES does not.

Example

char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the value placed into to, not including the terminating null character.

Errors

None.

24.2.3.54. mysql_real_query()

int mysql_real_query(MYSQL *mysql, const char *query, unsigned long length)

Description

Executes the SQL query pointed to by query, which should be a string length bytes long. Normally, the string must consist of a single SQL statement and you should not add a terminating semicolon (‘;’) or \g to the statement. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 24.2.9, “C API Handling of Multiple Statement Execution”.

You must use mysql_real_query() rather than mysql_query() for queries that contain binary data, because binary data may contain the ‘\0’ character. In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the query string.

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 24.2.3.22, “mysql_field_count().

Return Values

Zero if the query was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.55. mysql_refresh()

int mysql_refresh(MYSQL *mysql, unsigned int options)

Description

This functions flushes tables or caches, or resets replication server information. The connected user must have the RELOAD privilege.

The options argument is a bit mask composed from any combination of the following values. Multiple values can be OR'ed together to perform multiple operations with a single call.

  • REFRESH_GRANT

    Refresh the grant tables, like FLUSH PRIVILEGES.

  • REFRESH_LOG

    Flush the logs, like FLUSH LOGS.

  • REFRESH_TABLES

    Flush the table cache, like FLUSH TABLES.

  • REFRESH_HOSTS

    Flush the host cache, like FLUSH HOSTS.

  • REFRESH_STATUS

    Reset status variables, like FLUSH STATUS.

  • REFRESH_THREADS

    Flush the thread cache.

  • REFRESH_SLAVE

    On a slave replication server, reset the master server information and restart the slave, like RESET SLAVE.

  • REFRESH_MASTER

    On a master replication server, remove the binary log files listed in the binary log index and truncate the index file, like RESET MASTER.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.56. mysql_reload()

int mysql_reload(MYSQL *mysql)

Description

Asks the MySQL server to reload the grant tables. The connected user must have the RELOAD privilege.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL FLUSH PRIVILEGES statement instead.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.57. mysql_rollback()

my_bool mysql_rollback(MYSQL *mysql)

Description

Rolls back the current transaction.

The action of this function is subject to the value of the completion_type system variable. In particular, if the value of completion_type is 2, the server performs a release after terminating a transaction and closes the client connection. The client program should call mysql_close() to close the connection from the client side.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

24.2.3.58. mysql_row_seek()

MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a query result set. The offset value is a row offset that should be a value returned from mysql_row_tell() or from mysql_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_row_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_row_seek().

Errors

None.

24.2.3.59. mysql_row_tell()

MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)

Description

Returns the current position of the row cursor for the last mysql_fetch_row(). This value can be used as an argument to mysql_row_seek().

You should use mysql_row_tell() only after mysql_store_result(), not after mysql_use_result().

Return Values

The current offset of the row cursor.

Errors

None.

24.2.3.60. mysql_select_db()

int mysql_select_db(MYSQL *mysql, const char *db)

Description

Causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.61. mysql_set_character_set()

int mysql_set_character_set(MYSQL *mysql, char *csname)

Description

This function is used to set the default character set for the current connection. The string csname specifies a valid character set name. The connection collation becomes the default collation of the character set. This function works like the SET NAMES statement, but also sets the value of mysql->charset, and thus affects the character set used by mysql_real_escape_string()

This function was added in MySQL 5.0.7.

Return Values

Zero for success. Non-zero if an error occurred.

Example

MYSQL mysql;

mysql_init(&mysql);
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

if (!mysql_set_character_set(&mysql, "utf8")) 
{
    printf("New client character set: %s\n", 
           mysql_character_set_name(&mysql));
}

24.2.3.62. mysql_set_local_infile_default()

void
mysql_set_local_infile_default(MYSQL *mysql);

Description

Sets the LOAD LOCAL DATA INFILE handler callback functions to the defaults used internally by the C client library. The library calls this function automatically if mysql_set_local_infile_handler() has not been called or does not supply valid functions for each of its callbacks.

The mysql_set_local_infile_default() function was added in MySQL 4.1.2.

Return Values

None.

Errors

None.

24.2.3.63. mysql_set_local_infile_handler()

void
mysql_set_local_infile_handler(MYSQL *mysql,
      int (*local_infile_init)(void **, const char *, void *),
      int (*local_infile_read)(void *, char *, unsigned int),
      void (*local_infile_end)(void *),
      int (*local_infile_error)(void *, char*, unsigned int),
      void *userdata);

Description

This function installs callbacks to be used during the execution of LOAD DATA LOCAL INFILE statements. It enables application programs to exert control over local (client-side) data file reading. The arguments are the connection handler, a set of pointers to callback functions, and a pointer to a data area that the callbacks can use to share information.

To use mysql_set_local_infile_handler(), you must write the following callback functions:

int
local_infile_init(void **ptr, const char *filename, void *userdata);

The initialization function. This is called once to do any setup necessary, open the data file, allocate data structures, and so forth. The first void** argument is a pointer to a pointer. You can set the pointer (that is, *ptr) to a value that will be passed to each of the other callbacks (as a void*). The callbacks can use this pointed-to value to maintain state information. The userdata argument is the same value that is passed to mysql_set_local_infile_handler().

The initialization function should return zero for success, non-zero for an error.

int
local_infile_read(void *ptr, char *buf, unsigned int buf_len);

The data-reading function. This is called repeatedly to read the data file. buf points to the buffer where the read data should be stored, and buf_len is the maximum number of bytes that the callback can read and store in the buffer. (It can read fewer bytes, but should not read more.)

The return value is the number of bytes read, or zero when no more data could be read (this indicates EOF). Return a value less than zero if an error occurs.

void
local_infile_end(void *ptr)

The termination function. This is called once after local_infile_read() has returned zero (EOF) or an error. This function should deallocate any memory allocated by local_infile_init() and perform any other cleanup necessary. It is invoked even if the initalization function returns an error.

int
local_infile_error(void *ptr, 
                   char *error_msg, 
                   unsigned int error_msg_len);

The error-handling function. This is called to get a textual error message to return to the user in case any of your other functions returns an error. error_msg points to the buffer into which the message should be written, and error_msg_len is the length of the buffer. The message should be written as a null-terminated string, so the message can be at most error_msg_len–1 bytes long.

The return value is the error number.

Typically, the other callbacks store the error message in the data structure pointed to by ptr, so that local_infile_error() can copy the message from there into error_msg.

After calling mysql_set_local_infile_handler() in your C code and passing pointers to your callback functions, you can then issue a LOAD DATA LOCAL INFILE statement (for example, by using mysql_query()). The client library automatically invokes your callbacks. The filename specified in LOAD DATA LOCAL INFILE will be passed as the second parameter to the local_infile_init() callback.

The mysql_set_local_infile_handler() function was added in MySQL 4.1.2.

Return Values

None.

Errors

None.

24.2.3.64. mysql_set_server_option()

int mysql_set_server_option(MYSQL *mysql, enum enum_mysql_set_option option)

Description

Enables or disables an option for the connection. option can have one of the following values:

MYSQL_OPTION_MULTI_STATEMENTS_ONEnable multiple-statement support.
MYSQL_OPTION_MULTI_STATEMENTS_OFFDisable multiple-statement support.

If you enable multiple-statement support, you should retrieve results from calls to mysql_query() or mysql_real_query() by using a loop that calls mysql_next_result() to determine whether there are more results. For an example, see Section 24.2.9, “C API Handling of Multiple Statement Execution”.

Enabling multiple-statement support with MYSQL_OPTION_MULTI_STATEMENTS_ON does not have quite the same effect as enabling it by passing the CLIENT_MULTI_STATEMENTS flag to mysql_real_connect(): CLIENT_MULTI_STATEMENTS also enables CLIENT_MULTI_RESULTS. If you are using the CALL SQL statement in your programs, multiple-result support must be enabled; this means that MYSQL_OPTION_MULTI_STATEMENTS_ON by itself is insufficient to allow the use of CALL.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • ER_UNKNOWN_COM_ERROR

    The server didn't support mysql_set_server_option() (which is the case that the server is older than 4.1.1) or the server didn't support the option one tried to set.

24.2.3.65. mysql_shutdown()

int mysql_shutdown(MYSQL *mysql, enum mysql_enum_shutdown_level shutdown_level)

Description

Asks the database server to shut down. The connected user must have SHUTDOWN privileges. MySQL 5.1 servers support only one type of shutdown; shutdown_level must be equal to SHUTDOWN_DEFAULT. Additional shutdown levels are planned to make it possible to choose the desired level. Dynamically linked executables which have been compiled with older versions of the libmysqlclient headers and call mysql_shutdown() need to be used with the old libmysqlclient dynamic library.

The shutdown process is described in Section 5.2.7, “The Shutdown Process”.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.66. mysql_sqlstate()

const char *mysql_sqlstate(MYSQL *mysql)

Description

Returns a null-terminated string containing the SQLSTATE error code for the most recently executed SQL statement. The error code consists of five characters. '00000' means “no error”. The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix C, Error Codes and Messages.

SQLSTATE values returned by mysql_sqlstate() differ from MySQL-specific error numbers returned by mysql_errno(). For example, the mysql client program displays errors using the following format, where 1146 is the mysql_errno() value and '42S02' is the corresponding mysql_sqlstate() value:

shell> SELECT * FROM no_such_table;
ERROR 1146 (42S02): Table 'test.no_such_table' doesn't exist

Not all MySQL error numbers are mapped to SQLSTATE error codes. The value 'HY000' (general error) is used for unmapped error numbers.

Return Values

A null-terminated character string containing the SQLSTATE error code.

See Also

See Section 24.2.3.14, “mysql_errno(), Section 24.2.3.15, “mysql_error(), and Section 24.2.7.26, “mysql_stmt_sqlstate().

24.2.3.67. mysql_ssl_set()

int mysql_ssl_set(MYSQL *mysql, const char *key, const char *cert, const char *ca, const char *capath, const char *cipher)

Description

mysql_ssl_set() is used for establishing secure connections using SSL. It must be called before mysql_real_connect().

mysql_ssl_set() does nothing unless OpenSSL support is enabled in the client library.

mysql is the connection handler returned from mysql_init(). The other parameters are specified as follows:

  • key is the pathname to the key file.

  • cert is the pathname to the certificate file.

  • ca is the pathname to the certificate authority file.

  • capath is the pathname to a directory that contains trusted SSL CA certificates in pem format.

  • cipher is a list of allowable ciphers to use for SSL encryption.

Any unused SSL parameters may be given as NULL.

Return Values

This function always returns 0. If SSL setup is incorrect, mysql_real_connect() returns an error when you attempt to connect.

24.2.3.68. mysql_stat()

const char *mysql_stat(MYSQL *mysql)

Description

Returns a character string containing information similar to that provided by the mysqladmin status command. This includes uptime in seconds and the number of running threads, questions, reloads, and open tables.

Return Values

A character string describing the server status. NULL if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.69. mysql_store_result()

MYSQL_RES *mysql_store_result(MYSQL *mysql)

Description

You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN, CHECK TABLE, and so forth).

You don't have to call mysql_store_result() or mysql_use_result() for other queries, but it does not do any harm or cause any notable performance degradation if you call mysql_store_result() in all cases. You can detect if the query didn't have a result set by checking if mysql_store_result() returns 0 (more about this later on).

If you want to know whether the query should return a result set, you can use mysql_field_count() to check for this. See Section 24.2.3.22, “mysql_field_count().

mysql_store_result() reads the entire result of a query to the client, allocates a MYSQL_RES structure, and places the result into this structure.

mysql_store_result() returns a null pointer if the query didn't return a result set (if the query was, for example, an INSERT statement).

mysql_store_result() also returns a null pointer if reading of the result set failed. You can check whether an error occurred by checking if mysql_error() returns a non-empty string, if mysql_errno() returns non-zero, or if mysql_field_count() returns zero.

An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)

Once you have called mysql_store_result() and got a result back that isn't a null pointer, you may call mysql_num_rows() to find out how many rows are in the result set.

You can call mysql_fetch_row() to fetch rows from the result set, or mysql_row_seek() and mysql_row_tell() to obtain or set the current row position within the result set.

You must call mysql_free_result() once you are done with the result set.

See Section 24.2.13.1, “Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success”.

Return Values

A MYSQL_RES result structure with the results. NULL if an error occurred.

Errors

mysql_store_result() resets mysql_error() and mysql_errno() if it succeeds.

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.70. mysql_thread_id()

unsigned long mysql_thread_id(MYSQL *mysql)

Description

Returns the thread ID of the current connection. This value can be used as an argument to mysql_kill() to kill the thread.

If the connection is lost and you reconnect with mysql_ping(), the thread ID changes. This means you should not get the thread ID and store it for later. You should get it when you need it.

Return Values

The thread ID of the current connection.

Errors

None.

24.2.3.71. mysql_use_result()

MYSQL_RES *mysql_use_result(MYSQL *mysql)

Description

You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).

mysql_use_result() initiates a result set retrieval but does not actually read the result set into the client like mysql_store_result() does. Instead, each row must be retrieved individually by making calls to mysql_fetch_row(). This reads the result of a query directly from the server without storing it in a temporary table or local buffer, which is somewhat faster and uses much less memory than mysql_store_result(). The client allocates memory only for the current row and a communication buffer that may grow up to max_allowed_packet bytes.

On the other hand, you shouldn't use mysql_use_result() if you are doing a lot of processing for each row on the client side, or if the output is sent to a screen on which the user may type a ^S (stop scroll). This ties up the server and prevent other threads from updating any tables from which the data is being fetched.

When using mysql_use_result(), you must execute mysql_fetch_row() until a NULL value is returned, otherwise, the unfetched rows are returned as part of the result set for your next query. The C API gives the error Commands out of sync; you can't run this command now if you forget to do this!

You may not use mysql_data_seek(), mysql_row_seek(), mysql_row_tell(), mysql_num_rows(), or mysql_affected_rows() with a result returned from mysql_use_result(), nor may you issue other queries until mysql_use_result() has finished. (However, after you have fetched all the rows, mysql_num_rows() accurately returns the number of rows fetched.)

You must call mysql_free_result() once you are done with the result set.

When using the libmysqld embedded server, the memory benefits are essentially lost because memory usage incrementally increases with each row retrieved until mysql_free_result() is called.

Return Values

A MYSQL_RES result structure. NULL if an error occurred.

Errors

mysql_use_result() resets mysql_error() and mysql_errno() if it succeeds.

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.3.72. mysql_warning_count()

unsigned int mysql_warning_count(MYSQL *mysql)

Description

Returns the number of warnings generated during execution of the previous SQL statement.

Return Values

The warning count.

Errors

None.

24.2.4. C API Prepared Statements

The MySQL client/server protocol provides for the use of prepared statements. This capability uses the MYSQL_STMT statement handler data structure returned by the mysql_stmt_init() initialization function. Prepared execution is an efficient way to execute a statement more than once. The statement is first parsed to prepare it for execution. Then it is executed one or more times at a later time, using the statement handle returned by the initialization function.

Prepared execution is faster than direct execution for statements executed more than once, primarily because the query is parsed only once. In the case of direct execution, the query is parsed every time it is executed. Prepared execution also can provide a reduction of network traffic because for each execution of the prepared statement, it is necessary only to send the data for the parameters.

Prepared statements might not provide a performance increase in some situations. For best results, test your application both with prepared and non-prepared statements and choose whichever yields best performance.

Another advantage of prepared statements is that it uses a binary protocol that makes data transfer between client and server more efficient.

The following statements can be used as prepared statements: CREATE TABLE, DELETE, DO, INSERT, REPLACE, SELECT, SET, UPDATE, and most SHOW statements.

As of MySQL 5.1.10, the following additional statements are supported:

ANALYZE TABLE
OPTIMIZE TABLE
REPAIR TABLE

As of MySQL 5.1.12, the following additional statements are supported:

CACHE INDEX
CHANGE MASTER
CHECKSUM {TABLE | TABLES}
{CREATE | RENAME | DROP} DATABASE
{CREATE | RENAME | DROP} USER
FLUSH {TABLE | TABLES | TABLES WITH READ LOCK | HOSTS | PRIVILEGES
  | LOGS | STATUS | MASTER | SLAVE | DES_KEY_FILE | USER_RESOURCES}
GRANT
REVOKE
KILL
LOAD INDEX INTO CACHE
RESET {MASTER | SLAVE | QUERY CACHE}
SHOW BINLOG EVENTS
SHOW CREATE {PROCEDURE | FUNCTION | EVENT | TABLE | VIEW}
SHOW {AUTHORS | CONTRIBUTORS | WARNINGS | ERRORS}
SHOW {MASTER | BINARY} LOGS
SHOW {MASTER | SLAVE} STATUS
SLAVE {START | STOP}
INSTALL PLUGIN
UNINSTALL PLUGIN

Other statements are not yet supported in MySQL 5.1.

24.2.5. C API Prepared Statement Data types

Prepared statements use these data structures:

  • To prepare a statement, call mysql_stmt_init(), which returns a pointer to a MYSQL_STMT data structure.

  • To provide input parameters for a prepared statement, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_param(). To receive output column values, set up MYSQL_BIND structures and pass them to mysql_stmt_bind_result().

  • The MYSQL_TIME structure is used to transfer temporal data in both directions.

The following descriptions provide additional detail on the use of the prepared statement data types.

  • MYSQL_STMT

    This structure represents a prepared statement. A statement is created by calling mysql_stmt_init(), which returns a statement handle (that is, a pointer to a MYSQL_STMT). The handle is used for all subsequent operations with the statement until you close it with mysql_stmt_close().

    The MYSQL_STMT structure has no members that are for application use. Also, you should not try to make a copy of a MYSQL_STMT structure. There is no guarantee that such a copy will be usable.

    Multiple statement handles can be associated with a single connection. The limit on the number of handles depends on the available system resources.

  • MYSQL_BIND

    This structure is used both for statement input (data values sent to the server) and output (result values returned from the server):

    • For input, MYSQL_BIND is used with mysql_stmt_bind_param() to bind parameter data values to buffers for use by mysql_stmt_execute().

    • For output, MYSQL_BIND is used with mysql_stmt_bind_result() to bind result set buffers for use in fetching rows with mysql_stmt_fetch().

    To use a MYSQL_BIND structure, you should zero its contents to initialize it, and then set its members appropriately. For example, to declare and initialize an array of three MYSQL_BIND structures, use this code:

    MYSQL_BIND    bind[3];
    memset(bind, 0, sizeof(bind));
    

    The MYSQL_BIND structure contains the following members for use by application programs. A given member might are used for different purposes depending on whether the structure is used for input or output.

    • enum enum_field_types buffer_type

      The type of the buffer. The allowable buffer_type values are listed later in this section. For input, buffer_type indicates what type of value you are binding to a statement parameter. For output, it indicates what type of value you expect to receive in a result buffer.

    • void *buffer

      For input, this is a pointer to the buffer in which a statement parameter's data value is stored. For output, it is a pointer to the buffer in which to return a result set column value. For numeric data types, buffer should point to a variable of the proper C type. (If you are associating the variable with a column that has the UNSIGNED attribute, the variable should be an unsigned C type. Indicate whether the variable is signed or unsigned by using the is_unsigned member, described later in this list.) For date and time data types, buffer should point to a MYSQL_TIME structure. For character and binary string data types, buffer should point to a character buffer.

    • unsigned long buffer_length

      The actual size of *buffer in bytes. This indicates the maximum amount of data that can be stored in the buffer. For character and binary C data, the buffer_length value specifies the length of *buffer when used with mysql_stmt_bind_param() to specify input values, or the maximum number of output data bytes that can be fetched into the buffer when used with mysql_stmt_bind_result().

    • unsigned long *length

      A pointer to an unsigned long variable that indicates the actual number of bytes of data stored in *buffer. length is used for character or binary C data. For input parameter data binding, length points to an unsigned long variable that indicates the actual length of the parameter value stored in *buffer; this is used by mysql_stmt_execute(). For output value binding, the return value of mysql_stmt_fetch() determines the interpretation of the length. If mysql_stmt_fetch() returns 0, *length indicates the actual length of the parameter value. If mysql_stmt_fetch() returns MYSQL_DATA_TRUNCATED, *length indicates the non-truncated length of the parameter value. In this case, the minimum of *length and buffer_length indicates the actual length of the value.

      length is ignored for numeric and temporal data types because the length of the data value is determined by the buffer_type value.

    • my_bool *is_null

      This member points to a my_bool variable that is true if a value is NULL, false if it is not NULL. For input, set *is_null to true to indicate that you are passing a NULL value as a statement parameter. For output, this value is set to true after you fetch a row if the result set column value returned from the statement is NULL.

      is_null is a pointer to a boolean rather than a boolean scalar so that it can be used in the following way:

      • If your data values are always NULL, use MYSQL_TYPE_NULL to bind the column.

      • If your data values are always NOT NULL, set is_null = (my_bool*) 0.

      • In all other cases, you should set is_null to the address of a my_bool variable and change that variable's value appropriately between executions to indicate whether data values are NULL or NOT NULL.

    • my_bool is_unsigned

      This member is used for integer types. (These correspond to the MYSQL_TYPE_TINY, MYSQL_TYPE_SHORT, MYSQL_TYPE_LONG, and MYSQL_TYPE_LONGLONG type codes.) is_unsigned should be set to true for unsigned types and false for signed types.

    • my_bool *error

      For output, set this member to point to a my_bool variable to have truncation information for the parameter stored there after a row fetching operation. (Truncation reporting is enabled by default, but can be controlled by calling mysql_options() with the MYSQL_REPORT_DATA_TRUNCATION option.) When truncation reporting is enabled, mysql_stmt_fetch() returns MYSQL_DATA_TRUNCATED and *error is true in the MYSQL_BIND structures for parameters in which truncation occurred. Truncation indicates loss of sign or significant digits, or that a string was too long to fit in a column.

  • MYSQL_TIME

    This structure is used to send and receive DATE, TIME, DATETIME, and TIMESTAMP data directly to and from the server. Set the buffer_type member of a MYSQL_BIND structure to one of the temporal types (MYSQL_TYPE_TIME, MYSQL_TYPE_DATE, MYSQL_TYPE_DATETIME, MYSQL_TYPE_TIMESTAMP), and set the buffer member to point to a MYSQL_TIME structure.

    The MYSQL_TIME structure contains the following members:

    • unsigned int year

      The year.

    • unsigned int month

      The month of the year.

    • unsigned int day

      The day of the month.

    • unsigned int hour

      The hour of the day.

    • unsigned int minute

      The minute of the hour.

    • unsigned int second

      The second of the minute.

    • my_bool neg

      A boolean flag to indicate whether the time is negative.

    • unsigned long second_part

      The fractional part of the second in microseconds. This member currently is unused.

    Only those parts of a MYSQL_TIME structure that apply to a given type of temporal value are used: The year, month, and day elements are used for DATE, DATETIME, and TIMESTAMP values. The hour, minute, and second elements are used for TIME, DATETIME, and TIMESTAMP values. See Section 24.2.10, “C API Handling of Date and Time Values”.

The following table shows the allowable values that may be specified in the buffer_type member of MYSQL_BIND structures. The table also shows those SQL types that correspond most closely to each buffer_type value, and, for numeric and temporal types, the corresponding recommended C type.

The types are “recommended” because implicit type conversion may be performed in both directions. The buffer_type value controls the conversion that will be performed. For example, to fetch a SQL MEDIUMINT column value, you can specify a buffer_type value of MYSQL_TYPE_LONG and use a C variable of type int as the destination buffer. If you fetch a numeric column with a value of 255 into a char[4] character array, specify a buffer_type value of MYSQL_TYPE_STRING and the resulting value in the array will be a 4-byte string containing '255\0'.

To determine whether string values in a result set returned from the server contain binary or non-binary data, check whether the charsetnr value of the result set metadata is 63. If so, the character set is binary, which indicates binary rather than non-binary data. This enables you to distinguish between BINARY and CHAR, VARBINARY and VARCHAR, and BLOB and TEXT.

buffer_type ValueSQL TypeRecommended C Type
MYSQL_TYPE_BITBITunsigned long long int
MYSQL_TYPE_TINYTINYINTunsigned char
MYSQL_TYPE_SHORTSMALLINTshort int
MYSQL_TYPE_LONGINTint
MYSQL_TYPE_LONGLONGBIGINTlong long int
MYSQL_TYPE_FLOATFLOATfloat
MYSQL_TYPE_DOUBLEDOUBLEdouble
MYSQL_TYPE_NEWDECIMALDECIMALchar[]
MYSQL_TYPE_TIMETIMEMYSQL_TIME
MYSQL_TYPE_DATEDATEMYSQL_TIME
MYSQL_TYPE_DATETIMEDATETIMEMYSQL_TIME
MYSQL_TYPE_TIMESTAMPTIMESTAMPMYSQL_TIME
MYSQL_TYPE_STRINGCHAR/BINARYchar[]
MYSQL_TYPE_VAR_STRINGVARCHAR/VARBINARYchar[]
MYSQL_TYPE_TINY_BLOBTINYBLOB/TINYTEXTchar[]
MYSQL_TYPE_BLOBBLOB/TEXTchar[]
MYSQL_TYPE_MEDIUM_BLOBMEDIUMBLOB/MEDIUMTEXTchar[]
MYSQL_TYPE_LONG_BLOBLONGBLOB/LONGTEXTchar[]

24.2.6. C API Prepared Statement Function Overview

The functions available for prepared statement processing are summarized here and described in greater detail in a later section. See Section 24.2.7, “C API Prepared Statement Function Descriptions”.

FunctionDescription
mysql_stmt_affected_rows()Returns the number of rows changes, deleted, or inserted by prepared UPDATE, DELETE, or INSERT statement.
mysql_stmt_attr_get()Get value of an attribute for a prepared statement.
mysql_stmt_attr_set()Sets an attribute for a prepared statement.
mysql_stmt_bind_param()Associates application data buffers with the parameter markers in a prepared SQL statement.
mysql_stmt_bind_result()Associates application data buffers with columns in the result set.
mysql_stmt_close()Frees memory used by prepared statement.
mysql_stmt_data_seek()Seeks to an arbitrary row number in a statement result set.
mysql_stmt_errno()Returns the error number for the last statement execution.
mysql_stmt_error()Returns the error message for the last statement execution.
mysql_stmt_execute()Executes the prepared statement.
mysql_stmt_fetch()Fetches the next row of data from the result set and returns data for all bound columns.
mysql_stmt_fetch_column()Fetch data for one column of the current row of the result set.
mysql_stmt_field_count()Returns the number of result columns for the most recent statement.
mysql_stmt_free_result()Free the resources allocated to the statement handle.
mysql_stmt_init()Allocates memory for MYSQL_STMT structure and initializes it.
mysql_stmt_insert_id()Returns the ID generated for an AUTO_INCREMENT column by prepared statement.
mysql_stmt_num_rows()Returns total rows from the statement buffered result set.
mysql_stmt_param_count()Returns the number of parameters in a prepared SQL statement.
mysql_stmt_param_metadata()(Return parameter metadata in the form of a result set.) Currently, this function does nothing.
mysql_stmt_prepare()Prepares an SQL string for execution.
mysql_stmt_reset()Reset the statement buffers in the server.
mysql_stmt_result_metadata()Returns prepared statement metadata in the form of a result set.
mysql_stmt_row_seek()Seeks to a row offset in a statement result set, using value returned from mysql_stmt_row_tell().
mysql_stmt_row_tell()Returns the statement row cursor position.
mysql_stmt_send_long_data()Sends long data in chunks to server.
mysql_stmt_sqlstate()Returns the SQLSTATE error code for the last statement execution.
mysql_stmt_store_result()Retrieves the complete result set to the client.

Call mysql_stmt_init() to create a statement handle, then mysql_stmt_prepare to prepare it, mysql_stmt_bind_param() to supply the parameter data, and mysql_stmt_execute() to execute the statement. You can repeat the mysql_stmt_execute() by changing parameter values in the respective buffers supplied through mysql_stmt_bind_param().

If the statement is a SELECT or any other statement that produces a result set, mysql_stmt_prepare() also returns the result set metadata information in the form of a MYSQL_RES result set through mysql_stmt_result_metadata().

You can supply the result buffers using mysql_stmt_bind_result(), so that the mysql_stmt_fetch() automatically returns data to these buffers. This is row-by-row fetching.

You can also send the text or binary data in chunks to server using mysql_stmt_send_long_data(). See Section 24.2.7.25, “mysql_stmt_send_long_data().

When statement execution has been completed, the statement handle must be closed using mysql_stmt_close() so that all resources associated with it can be freed.

If you obtained a SELECT statement's result set metadata by calling mysql_stmt_result_metadata(), you should also free the metadata using mysql_free_result().

Execution Steps

To prepare and execute a statement, an application follows these steps:

  1. Create a prepared statement handle with mysql_stmt_init(). To prepare the statement on the server, call mysql_stmt_prepare() and pass it a string containing the SQL statement.

  2. If the statement produces a result set, call mysql_stmt_result_metadata() to obtain the result set metadata. This metadata is itself in the form of result set, albeit a separate one from the one that contains the rows returned by the query. The metadata result set indicates how many columns are in the result and contains information about each column.

  3. Set the values of any parameters using mysql_stmt_bind_param(). All parameters must be set. Otherwise, statement execution returns an error or produces unexpected results.

  4. Call mysql_stmt_execute() to execute the statement.

  5. If the statement produces a result set, bind the data buffers to use for retrieving the row values by calling mysql_stmt_bind_result().

  6. Fetch the data into the buffers row by row by calling mysql_stmt_fetch() repeatedly until no more rows are found.

  7. Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the statement.

When mysql_stmt_prepare() is called, the MySQL client/server protocol performs these actions:

  • The server parses the statement and sends the okay status back to the client by assigning a statement ID. It also sends total number of parameters, a column count, and its metadata if it is a result set oriented statement. All syntax and semantics of the statement are checked by the server during this call.

  • The client uses this statement ID for the further operations, so that the server can identify the statement from among its pool of statements.

When mysql_stmt_execute() is called, the MySQL client/server protocol performs these actions:

  • The client uses the statement handle and sends the parameter data to the server.

  • The server identifies the statement using the ID provided by the client, replaces the parameter markers with the newly supplied data, and executes the statement. If the statement produces a result set, the server sends the data back to the client. Otherwise, it sends an okay status and total number of rows changed, deleted, or inserted.

When mysql_stmt_fetch() is called, the MySQL client/server protocol performs these actions:

  • The client reads the data from the packet row by row and places it into the application data buffers by doing the necessary conversions. If the application buffer type is same as that of the field type returned from the server, the conversions are straightforward.

If an error occurs, you can get the statement error code, error message, and SQLSTATE value using mysql_stmt_errno(), mysql_stmt_error(), and mysql_stmt_sqlstate(), respectively.

Prepared Statement Logging

For prepared statements that are executed with the mysql_stmt_prepare() and mysql_stmt_execute() C API functions, the server writes Prepare and Execute lines to the general query log so that you can tell when statements are prepared and executed.

Suppose that you prepare and execute a statement as follows:

  1. Call mysql_stmt_prepare() to prepare the statement string "SELECT ?".

  2. Call mysql_stmt_bind_param() to bind the value 3 to the parameter in the prepared statement.

  3. Call mysql_stmt_execute() to execute the prepared statement.

As a result of the preceding calls, the server writes the following lines to the general query log:

Prepare  [1] SELECT ?
Execute  [1] SELECT 3

Each Prepare and Execute line in the log is tagged with a [N] statement identifier so that you can keep track of which prepared statement is being logged. N is a positive integer. If there are multiple prepared statements active simultaneously for the client, N may be greater than 1. Each Execute lines shows a prepared statement after substitution of data values for ? parameters.

Version notes: Prepare lines are displayed without [N] before MySQL 4.1.10. Execute lines are not displayed at all before MySQL 4.1.10.

24.2.7. C API Prepared Statement Function Descriptions

To prepare and execute queries, use the functions described in detail in the following sections.

Note that all functions operating with a MYSQL_STMT structure begin with the prefix mysql_stmt_.

To create a MYSQL_STMT handle, use the mysql_stmt_init() function.

24.2.7.1. mysql_stmt_affected_rows()

my_ulonglong mysql_stmt_affected_rows(MYSQL_STMT *stmt)

Description

Returns the total number of rows changed, deleted, or inserted by the last executed statement. May be called immediately after mysql_stmt_execute() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_stmt_affected_rows() works like mysql_num_rows().

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query, or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_stmt_affected_rows() was called prior to calling mysql_stmt_store_result(). Because mysql_stmt_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

See Section 24.2.3.1, “mysql_affected_rows(), for additional information on the return value.

Errors

None.

Example

For the usage of mysql_stmt_affected_rows(), refer to the Example from Section 24.2.7.10, “mysql_stmt_execute().

24.2.7.2. mysql_stmt_attr_get()

int mysql_stmt_attr_get(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, void *arg)

Description

Can be used to get the current value for a statement attribute.

The option argument is the option that you want to get; the arg should point to a variable that should contain the option value. If the option is an integer, then arg should point to the value of the integer.

See Section 24.2.7.3, “mysql_stmt_attr_set(), for a list of options and option types.

Return Values

0 if okay. Non-zero if option is unknown.

Errors

None.

24.2.7.3. mysql_stmt_attr_set()

int mysql_stmt_attr_set(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, const void *arg)

Description

Can be used to affect behavior for a prepared statement. This function may be called multiple times to set several options.

The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, then arg should point to the value of the integer.

Possible option values:

OptionArgument TypeFunction
STMT_ATTR_UPDATE_MAX_LENGTHmy_bool *If set to 1: Update metadata MYSQL_FIELD->max_length in mysql_stmt_store_result().
STMT_ATTR_CURSOR_TYPEunsigned long *Type of cursor to open for statement when mysql_stmt_execute() is invoked. *arg can be CURSOR_TYPE_NO_CURSOR (the default) or CURSOR_TYPE_READ_ONLY.
STMT_ATTR_PREFETCH_ROWSunsigned long *Number of rows to fetch from server at a time when using a cursor. *arg can be in the range from 1 to the maximum value of unsigned long. The default is 1.

If you use the STMT_ATTR_CURSOR_TYPE option with CURSOR_TYPE_READ_ONLY, a cursor is opened for the statement when you invoke mysql_stmt_execute(). If there is already an open cursor from a previous mysql_stmt_execute() call, it closes the cursor before opening a new one. mysql_stmt_reset() also closes any open cursor before preparing the statement for re-execution. mysql_stmt_free_result() closes any open cursor.

If you open a cursor for a prepared statement, mysql_stmt_store_result() is unnecessary, because that function causes the result set to be buffered on the client side.

The STMT_ATTR_CURSOR_TYPE option was added in MySQL 5.0.2. The STMT_ATTR_PREFETCH_ROWS option was added in MySQL 5.0.6.

Return Values

0 if okay. Non-zero if option is unknown.

Errors

None.

Example

The following example opens a cursor for a prepared statement and sets the number of rows to fetch at a time to 5:

MYSQL_STMT *stmt;
int rc;
unsigned long type;
unsigned long prefetch_rows = 5;

stmt = mysql_stmt_init(mysql);
type = (unsigned long) CURSOR_TYPE_READ_ONLY;
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, (void*) &type);
/* ... check return value ... */
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_PREFETCH_ROWS,
                         (void*) &prefetch_rows);
/* ... check return value ... */

24.2.7.4. mysql_stmt_bind_param()

my_bool mysql_stmt_bind_param(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_param() is used to bind input data for the parameter markers in the SQL statement that was passed to mysql_stmt_prepare(). It uses MYSQL_BIND structures to supply the data. bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each ‘?’ parameter marker that is present in the query.

Suppose that you prepare the following statement:

INSERT INTO mytbl VALUES(?,?,?)

When you bind the parameters, the array of MYSQL_BIND structures must contain three elements, and can be declared like this:

MYSQL_BIND bind[3];

Section 24.2.5, “C API Prepared Statement Data types”, describes the members of each MYSQL_BIND element and how they should be set to provide input values.

Return Values

Zero if the bind operation was successful. Non-zero if an error occurred.

Errors

  • CR_INVALID_BUFFER_USE

    Indicates if the bind is to supply the long data in chunks and if the buffer type is non string or binary.

  • CR_UNSUPPORTED_PARAM_TYPE

    The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_bind_param(), refer to the Example from Section 24.2.7.10, “mysql_stmt_execute().

24.2.7.5. mysql_stmt_bind_result()

my_bool mysql_stmt_bind_result(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_result() is used to associate (that is, bind) output columns in the result set to data buffers and length buffers. When mysql_stmt_fetch() is called to fetch data, the MySQL client/server protocol places the data for the bound columns into the specified buffers.

All columns must be bound to buffers prior to calling mysql_stmt_fetch(). bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain one element for each column of the result set. If you do not bind columns to MYSQL_BIND structures, mysql_stmt_fetch() simply ignores the data fetch. The buffers should be large enough to hold the data values, because the protocol doesn't return data values in chunks.

A column can be bound or rebound at any time, even after a result set has been partially retrieved. The new binding takes effect the next time mysql_stmt_fetch() is called. Suppose that an application binds the columns in a result set and calls mysql_stmt_fetch(). The client/server protocol returns data in the bound buffers. Then suppose that the application binds the columns to a different set of buffers. The protocol places data into the newly bound buffers when the next call to mysql_stmt_fetch() occurs.

To bind a column, an application calls mysql_stmt_bind_result() and passes the type, address, and the address of the length buffer. Section 24.2.5, “C API Prepared Statement Data types”, describes the members of each MYSQL_BIND element and how they should be set to receive output values.

Return Values

Zero if the bind operation was successful. Non-zero if an error occurred.

Errors

  • CR_UNSUPPORTED_PARAM_TYPE

    The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_bind_result(), refer to the Example from Section 24.2.7.11, “mysql_stmt_fetch().

24.2.7.6. mysql_stmt_close()

my_bool mysql_stmt_close(MYSQL_STMT *)

Description

Closes the prepared statement. mysql_stmt_close() also deallocates the statement handle pointed to by stmt.

If the current statement has pending or unread results, this function cancels them so that the next query can be executed.

Return Values

Zero if the statement was freed successfully. Non-zero if an error occurred.

Errors

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_close(), refer to the Example from Section 24.2.7.10, “mysql_stmt_execute().

24.2.7.7. mysql_stmt_data_seek()

void mysql_stmt_data_seek(MYSQL_STMT *stmt, my_ulonglong offset)

Description

Seeks to an arbitrary row in a statement result set. The offset value is a row number and should be in the range from 0 to mysql_stmt_num_rows(stmt)-1.

This function requires that the statement result set structure contains the entire result of the last executed query, so mysql_stmt_data_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

None.

Errors

None.

24.2.7.8. mysql_stmt_errno()

unsigned int mysql_stmt_errno(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_errno() returns the error code for the most recently invoked statement API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL errmsg.h header file. Server error message numbers are listed in mysqld_error.h. Errors also are listed at Appendix C, Error Codes and Messages.

Return Values

An error code value. Zero if no error occurred.

Errors

None.

24.2.7.9. mysql_stmt_error()

const char *mysql_stmt_error(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_error() returns a null-terminated string containing the error message for the most recently invoked statement API function that can succeed or fail. An empty string ("") is returned if no error occurred. This means the following two tests are equivalent:

if(*mysql_stmt_errno(stmt))
{
  // an error occurred
}

if (mysql_stmt_error(stmt)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently, you can choose error messages in several different languages.

Return Values

A character string that describes the error. An empty string if no error occurred.

Errors

None.

24.2.7.10. mysql_stmt_execute()

int mysql_stmt_execute(MYSQL_STMT *stmt)

Description

mysql_stmt_execute() executes the prepared query associated with the statement handle. The currently bound parameter marker values are sent to server during this call, and the server replaces the markers with this newly supplied data.

If the statement is an UPDATE, DELETE, or INSERT, the total number of changed, deleted, or inserted rows can be found by calling mysql_stmt_affected_rows(). If this is a statement such as SELECT that generates a result set, you must call mysql_stmt_fetch() to fetch the data prior to calling any other functions that result in query processing. For more information on how to fetch the results, refer to Section 24.2.7.11, “mysql_stmt_fetch().

For statements that generate a result set, you can request that mysql_stmt_execute() open a cursor for the statement by calling mysql_stmt_attr_set() before executing the statement. If you execute a statement multiple times, mysql_stmt_execute() closes any open cursor before opening a new one.

Return Values

Zero if execution was successful. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

The following example demonstrates how to create and populate a table using mysql_stmt_init(), mysql_stmt_prepare(), mysql_stmt_param_count(), mysql_stmt_bind_param(), mysql_stmt_execute(), and mysql_stmt_affected_rows(). The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table"
#define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(col1 INT,\
                                                 col2 VARCHAR(40),\
                                                 col3 SMALLINT,\
                                                 col4 TIMESTAMP)"
#define INSERT_SAMPLE "INSERT INTO \ 
                       test_table(col1,col2,col3) \
                       VALUES(?,?,?)"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[3];
my_ulonglong  affected_rows;
int           param_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
unsigned long str_length;
my_bool       is_null;

if (mysql_query(mysql, DROP_SAMPLE_TABLE))
{
  fprintf(stderr, " DROP TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

if (mysql_query(mysql, CREATE_SAMPLE_TABLE))
{
  fprintf(stderr, " CREATE TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

/* Prepare an INSERT query with 3 parameters */
/* (the TIMESTAMP column is not named; the server */
/*  sets it to the current date and time) */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_SAMPLE, strlen(INSERT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, INSERT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in INSERT: %d\n", param_count);

if (param_count != 3) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Bind the data for all 3 parameters */

memset(bind, 0, sizeof(bind));

/* INTEGER PARAM */
/* This is a number type, so there is no need 
   to specify buffer_length */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= 0;
bind[0].length= 0;

/* STRING PARAM */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= 0;
bind[1].length= &str_length;

/* SMALLINT PARAM */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null;
bind[2].length= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_param() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Specify the data values for the first row */
int_data= 10;             /* integer */
strncpy(str_data, "MySQL", STRING_SIZE); /* string  */
str_length= strlen(str_data);

/* INSERT SMALLINT data as NULL */
is_null= 1;

/* Execute the INSERT statement - 1*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the total number of affected rows */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 1): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Specify data values for second row, 
   then re-execute the statement */
int_data= 1000;
strncpy(str_data, "
        The most popular Open Source database", 
        STRING_SIZE);
str_length= strlen(str_data);
small_data= 1000;         /* smallint */
is_null= 0;               /* reset */

/* Execute the INSERT statement - 2*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute, 2 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get the total rows affected */
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 2): %lu\n",
                (unsigned long) affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

Note: For complete examples on the use of prepared statement functions, refer to the file tests/mysql_client_test.c. This file can be obtained from a MySQL source distribution or from the BitKeeper source repository.

24.2.7.11. mysql_stmt_fetch()

int mysql_stmt_fetch(MYSQL_STMT *stmt)

Description

mysql_stmt_fetch() returns the next row in the result set. It can be called only while the result set exists; that is, after a call to mysql_stmt_execute() that creates a result set or after mysql_stmt_store_result(), which is called after mysql_stmt_execute() to buffer the entire result set.

mysql_stmt_fetch() returns row data using the buffers bound by mysql_stmt_bind_result(). It returns the data in those buffers for all the columns in the current row set and the lengths are returned to the length pointer.

All columns must be bound by the application before calling mysql_stmt_fetch().

If a fetched data value is a NULL value, the *is_null value of the corresponding MYSQL_BIND structure contains TRUE (1). Otherwise, the data and its length are returned in the *buffer and *length elements based on the buffer type specified by the application. Each numeric and temporal type has a fixed length, as listed in the following table. The length of the string types depends on the length of the actual data value, as indicated by data_length.

TypeLength
MYSQL_TYPE_TINY1
MYSQL_TYPE_SHORT2
MYSQL_TYPE_LONG4
MYSQL_TYPE_LONGLONG8
MYSQL_TYPE_FLOAT4
MYSQL_TYPE_DOUBLE8
MYSQL_TYPE_TIMEsizeof(MYSQL_TIME)
MYSQL_TYPE_DATEsizeof(MYSQL_TIME)
MYSQL_TYPE_DATETIMEsizeof(MYSQL_TIME)
MYSQL_TYPE_STRINGdata length
MYSQL_TYPE_BLOBdata_length

Return Values

Return ValueDescription
0Successful, the data has been fetched to application data buffers.
1Error occurred. Error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().
MYSQL_NO_DATANo more rows/data exists
MYSQL_DATA_TRUNCATEDData truncation occurred

MYSQL_DATA_TRUNCATED is returned when truncation reporting is enabled. (Reporting is enabled by default, but can be controlled with mysql_options().) To determine which parameters were truncated when this value is returned, check the error members of the MYSQL_BIND parameter structures.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

  • CR_UNSUPPORTED_PARAM_TYPE

    The buffer type is MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, but the data type is not DATE, TIME, DATETIME, or TIMESTAMP.

  • All other unsupported conversion errors are returned from mysql_stmt_bind_result().

Example

The following example demonstrates how to fetch data from a table using mysql_stmt_result_metadata(), mysql_stmt_bind_result(), and mysql_stmt_fetch(). (This example expects to retrieve the two rows inserted by the example shown in Section 24.2.7.10, “mysql_stmt_execute().) The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define SELECT_SAMPLE "SELECT col1, col2, col3, col4 \
                       FROM test_table"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[4];
MYSQL_RES     *prepare_meta_result;
MYSQL_TIME    ts;
unsigned long length[4];
int           param_count, column_count, row_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
my_bool       is_null[4];
my_bool       error[4];

/* Prepare a SELECT query to fetch data from test_table */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, SELECT_SAMPLE, strlen(SELECT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), SELECT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, SELECT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in SELECT: %d\n", param_count);

if (param_count != 0) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Fetch result set meta information */
prepare_meta_result = mysql_stmt_result_metadata(stmt);
if (!prepare_meta_result)
{
  fprintf(stderr,
         " mysql_stmt_result_metadata(), \ 
           returned no meta information\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get total columns in the query */
column_count= mysql_num_fields(prepare_meta_result);
fprintf(stdout, 
        " total columns in SELECT statement: %d\n", 
        column_count);

if (column_count != 4) /* validate column count */
{
  fprintf(stderr, " invalid column count returned by MySQL\n");
  exit(0);
}

/* Execute the SELECT query */
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Bind the result buffers for all 4 columns before fetching them */

memset(bind, 0, sizeof(bind));

/* INTEGER COLUMN */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= &is_null[0];
bind[0].length= &length[0];
bind[0].error= &error[0];

/* STRING COLUMN */
bind[1].buffer_type= MYSQL_TYPE_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= &is_null[1];
bind[1].length= &length[1];
bind[1].error= &error[1];

/* SMALLINT COLUMN */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;
bind[2].is_null= &is_null[2];
bind[2].length= &length[2];
bind[2].error= &error[2];

/* TIMESTAMP COLUMN */
bind[3].buffer_type= MYSQL_TYPE_TIMESTAMP;
bind[3].buffer= (char *)&ts;
bind[3].is_null= &is_null[3];
bind[3].length= &length[3];
bind[3].error= &error[3];

/* Bind the result buffers */
if (mysql_stmt_bind_result(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Now buffer all results to client */
if (mysql_stmt_store_result(stmt))
{
  fprintf(stderr, " mysql_stmt_store_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Fetch all rows */
row_count= 0;
fprintf(stdout, "Fetching results ...\n");
while (!mysql_stmt_fetch(stmt))
{
  row_count++;
  fprintf(stdout, "  row %d\n", row_count);

  /* column 1 */
  fprintf(stdout, "   column1 (integer)  : ");
  if (is_null[0])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", int_data, length[0]);

  /* column 2 */
  fprintf(stdout, "   column2 (string)   : ");
  if (is_null[1])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %s(%ld)\n", str_data, length[1]);

  /* column 3 */
  fprintf(stdout, "   column3 (smallint) : ");
  if (is_null[2])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", small_data, length[2]);

  /* column 4 */
  fprintf(stdout, "   column4 (timestamp): ");
  if (is_null[3])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %04d-%02d-%02d %02d:%02d:%02d (%ld)\n",
                     ts.year, ts.month, ts.day,
                     ts.hour, ts.minute, ts.second,
                     length[3]);
  fprintf(stdout, "\n");
}

/* Validate rows fetched */
fprintf(stdout, " total rows fetched: %d\n", row_count);
if (row_count != 2)
{
  fprintf(stderr, " MySQL failed to return all rows\n");
  exit(0);
}

/* Free the prepared result metadata */
mysql_free_result(prepare_meta_result);


/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

24.2.7.12. mysql_stmt_fetch_column()

int mysql_stmt_fetch_column(MYSQL_STMT *stmt, MYSQL_BIND *bind, unsigned int column, unsigned long offset)

Description

Fetch one column from the current result set row. bind provides the buffer where data should be placed. It should be set up the same way as for mysql_stmt_bind_result(). column indicates which column to fetch. The first column is numbered 0. offset is the offset within the data value at which to begin retrieving data. This can be used for fetching the data value in pieces. The beginning of the value is offset 0.

Return Values

Zero if the value was fetched successfully. Non-zero if an error occurred.

Errors

  • CR_INVALID_PARAMETER_NO

    Invalid column number.

  • CR_NO_DATA

    The end of the result set has already been reached.

24.2.7.13. mysql_stmt_field_count()

unsigned int mysql_stmt_field_count(MYSQL_STMT *stmt)

Description

Returns the number of columns for the most recent statement for the statement handler. This value is zero for statements such as INSERT or DELETE that do not produce result sets.

mysql_stmt_field_count() can be called after you have prepared a statement by invoking mysql_stmt_prepare().

Return Values

An unsigned integer representing the number of columns in a result set.

Errors

None.

24.2.7.14. mysql_stmt_free_result()

my_bool mysql_stmt_free_result(MYSQL_STMT *stmt)

Description

Releases memory associated with the result set produced by execution of the prepared statement. If there is a cursor open for the statement, mysql_stmt_free_result() closes it.

Return Values

Zero if the result set was freed successfully. Non-zero if an error occurred.

Errors

24.2.7.15. mysql_stmt_init()

MYSQL_STMT *mysql_stmt_init(MYSQL *mysql)

Description

Create a MYSQL_STMT handle. The handle should be freed with mysql_stmt_close(MYSQL_STMT *).

Return values

A pointer to a MYSQL_STMT structure in case of success. NULL if out of memory.

Errors

  • CR_OUT_OF_MEMORY

    Out of memory.

24.2.7.16. mysql_stmt_insert_id()

my_ulonglong mysql_stmt_insert_id(MYSQL_STMT *stmt)

Description

Returns the value generated for an AUTO_INCREMENT column by the prepared INSERT or UPDATE statement. Use this function after you have executed a prepared INSERT statement on a table which contains an AUTO_INCREMENT field.

See Section 24.2.3.37, “mysql_insert_id(), for more information.

Return Values

Value for AUTO_INCREMENT column which was automatically generated or explicitly set during execution of prepared statement, or value generated by LAST_INSERT_ID(expr) function. Return value is undefined if statement does not set AUTO_INCREMENT value.

Errors

None.

24.2.7.17. mysql_stmt_num_rows()

my_ulonglong mysql_stmt_num_rows(MYSQL_STMT *stmt)

Description

Returns the number of rows in the result set.

The use of mysql_stmt_num_rows() depends on whether you used mysql_stmt_store_result() to buffer the entire result set in the statement handle.

If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately.

mysql_stmt_num_rows() is intended for use with statements that return a result set, such as SELECT. For statements such as INSERT, UPDATE, or DELETE, the number of affected rows can be obtained with mysql_stmt_affected_rows().

Return Values

The number of rows in the result set.

Errors

None.

24.2.7.18. mysql_stmt_param_count()

unsigned long mysql_stmt_param_count(MYSQL_STMT *stmt)

Description

Returns the number of parameter markers present in the prepared statement.

Return Values

An unsigned long integer representing the number of parameters in a statement.

Errors

None.

Example

For the usage of mysql_stmt_param_count(), refer to the Example from Section 24.2.7.10, “mysql_stmt_execute().

24.2.7.19. mysql_stmt_param_metadata()

MYSQL_RES *mysql_stmt_param_metadata(MYSQL_STMT *stmt)

This function currently does nothing.

Description

Return Values

Errors

24.2.7.20. mysql_stmt_prepare()

int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, unsigned long length)

Description

Given the statement handle returned by mysql_stmt_init(), prepares the SQL statement pointed to by the string query and returns a status value. The string length should be given by the length argument. The string must consist of a single SQL statement. You should not add a terminating semicolon (‘;’) or \g to the statement.

The application can include one or more parameter markers in the SQL statement by embedding question mark (‘?’) characters into the SQL string at the appropriate positions.

The markers are legal only in certain places in SQL statements. For example, they are allowed in the VALUES() list of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value. However, they are not allowed for identifiers (such as table or column names), or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. In general, parameters are legal only in Data Manipulation Language (DML) statements, and not in Data Definition Language (DDL) statements.

The parameter markers must be bound to application variables using mysql_stmt_bind_param() before executing the statement.

Return Values

Zero if the statement was prepared successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

If the prepare operation was unsuccessful (that is, mysql_stmt_prepare() returns non-zero), the error message can be obtained by calling mysql_stmt_error().

Example

For the usage of mysql_stmt_prepare(), refer to the Example from Section 24.2.7.10, “mysql_stmt_execute().

24.2.7.21. mysql_stmt_reset()

my_bool mysql_stmt_reset(MYSQL_STMT *stmt)

Description

Reset the prepared statement on the client and server to state after prepare. This is mainly used to reset data sent with mysql_stmt_send_long_data(). Any open cursor for the statement is closed.

To re-prepare the statement with another query, use mysql_stmt_prepare().

Return Values

Zero if the statement was reset successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.7.22. mysql_stmt_result_metadata()

MYSQL_RES *mysql_stmt_result_metadata(MYSQL_STMT *stmt)

Description

If a statement passed to mysql_stmt_prepare() is one that produces a result set, mysql_stmt_result_metadata() returns the result set metadata in the form of a pointer to a MYSQL_RES structure that can be used to process the meta information such as total number of fields and individual field information. This result set pointer can be passed as an argument to any of the field-based API functions that process result set metadata, such as:

  • mysql_num_fields()

  • mysql_fetch_field()

  • mysql_fetch_field_direct()

  • mysql_fetch_fields()

  • mysql_field_count()

  • mysql_field_seek()

  • mysql_field_tell()

  • mysql_free_result()

The result set structure should be freed when you are done with it, which you can do by passing it to mysql_free_result(). This is similar to the way you free a result set obtained from a call to mysql_store_result().

The result set returned by mysql_stmt_result_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handle with mysql_stmt_fetch().

Return Values

A MYSQL_RES result structure. NULL if no meta information exists for the prepared query.

Errors

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

For the usage of mysql_stmt_result_metadata(), refer to the Example from Section 24.2.7.11, “mysql_stmt_fetch().

24.2.7.23. mysql_stmt_row_seek()

MYSQL_ROW_OFFSET mysql_stmt_row_seek(MYSQL_STMT *stmt, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a statement result set. The offset value is a row offset that should be a value returned from mysql_stmt_row_tell() or from mysql_stmt_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_stmt_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_stmt_row_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_stmt_row_seek().

Errors

None.

24.2.7.24. mysql_stmt_row_tell()

MYSQL_ROW_OFFSET mysql_stmt_row_tell(MYSQL_STMT *stmt)

Description

Returns the current position of the row cursor for the last mysql_stmt_fetch(). This value can be used as an argument to mysql_stmt_row_seek().

You should use mysql_stmt_row_tell() only after mysql_stmt_store_result().

Return Values

The current offset of the row cursor.

Errors

None.

24.2.7.25. mysql_stmt_send_long_data()

my_bool mysql_stmt_send_long_data(MYSQL_STMT *stmt, unsigned int parameter_number, const char *data, unsigned long length)

Description

Allows an application to send parameter data to the server in pieces (or “chunks”). This function can be called multiple times to send the parts of a character or binary data value for a column, which must be one of the TEXT or BLOB data types.

parameter_number indicates which parameter to associate the data with. Parameters are numbered beginning with 0. data is a pointer to a buffer containing data to be sent, and length indicates the number of bytes in the buffer.

Note: The next mysql_stmt_execute() call ignores the bind buffer for all parameters that have been used with mysql_stmt_send_long_data() since last mysql_stmt_execute() or mysql_stmt_reset().

If you want to reset/forget the sent data, you can do it with mysql_stmt_reset(). See Section 24.2.7.21, “mysql_stmt_reset().

Return Values

Zero if the data is sent successfully to server. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

Example

The following example demonstrates how to send the data for a TEXT column in chunks. It inserts the data value 'MySQL - The most popular Open Source database' into the text_column column. The mysql variable is assumed to be a valid connection handle.

#define INSERT_QUERY "INSERT INTO \
                      test_long_data(text_column) VALUES(?)"

MYSQL_BIND bind[1];
long       length;

stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_QUERY, strlen(INSERT_QUERY)))
{
  fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}
 memset(bind, 0, sizeof(bind));
 bind[0].buffer_type= MYSQL_TYPE_STRING;
 bind[0].length= &length;
 bind[0].is_null= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, "\n param bind failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply data in chunks to server */
 if (mysql_stmt_send_long_data(stmt,0,"MySQL",5))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply the next piece of data */
 if (mysql_stmt_send_long_data(stmt,0,
           " - The most popular Open Source database",40))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Now, execute the query */
 if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, "\n mysql_stmt_execute failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

24.2.7.26. mysql_stmt_sqlstate()

const char *mysql_stmt_sqlstate(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_sqlstate() returns a null-terminated string containing the SQLSTATE error code for the most recently invoked prepared statement API function that can succeed or fail. The error code consists of five characters. "00000" means “no error.” The values are specified by ANSI SQL and ODBC. For a list of possible values, see Appendix C, Error Codes and Messages.

Note that not all MySQL errors are yet mapped to SQLSTATE codes. The value "HY000" (general error) is used for unmapped errors.

Return Values

A null-terminated character string containing the SQLSTATE error code.

24.2.7.27. mysql_stmt_store_result()

int mysql_stmt_store_result(MYSQL_STMT *stmt)

Description

You must call mysql_stmt_store_result() for every statement that successfully produces a result set (SELECT, SHOW, DESCRIBE, EXPLAIN), and only if you want to buffer the complete result set by the client, so that the subsequent mysql_stmt_fetch() call returns buffered data.

It is unnecessary to call mysql_stmt_store_result() for other statements, but if you do, it does not harm or cause any notable performance problem. You can detect whether the statement produced a result set by checking if mysql_stmt_result_metadata() returns NULL. For more information, refer to Section 24.2.7.22, “mysql_stmt_result_metadata().

Note: MySQL doesn't by default calculate MYSQL_FIELD->max_length for all columns in mysql_stmt_store_result() because calculating this would slow down mysql_stmt_store_result() considerably and most applications doesn't need max_length. If you want max_length to be updated, you can call mysql_stmt_attr_set(MYSQL_STMT, STMT_ATTR_UPDATE_MAX_LENGTH, &flag) to enable this. See Section 24.2.7.3, “mysql_stmt_attr_set().

Return Values

Zero if the results are buffered successfully. Non-zero if an error occurred.

Errors

  • CR_COMMANDS_OUT_OF_SYNC

    Commands were executed in an improper order.

  • CR_OUT_OF_MEMORY

    Out of memory.

  • CR_SERVER_GONE_ERROR

    The MySQL server has gone away.

  • CR_SERVER_LOST

    The connection to the server was lost during the query.

  • CR_UNKNOWN_ERROR

    An unknown error occurred.

24.2.8. C API Prepared statement problems

Here follows a list of the currently known problems with prepared statements:

  • TIME, TIMESTAMP, and DATETIME do not support parts of seconds (for example from DATE_FORMAT().

  • When converting an integer to string, ZEROFILL is honored with prepared statements in some cases where the MySQL server doesn't print the leading zeros. (For example, with MIN(number-with-zerofill)).

  • When converting a floating point number to a string in the client, the rightmost digits of the converted value may differ slightly from those of the original value.

  • Prepared statements do not use the Query Cache, even in cases where a query does not contain any placeholders. See Section 5.14.1, “How the Query Cache Operates”.

  • Prepared statements do not support multi-statements (that is, multiple statements within a single string separated by ‘;’ characters). This also means that prepared statements cannot invoke stored procedures that return result sets, because prepared statements do not support multiple result sets.

24.2.9. C API Handling of Multiple Statement Execution

MySQL 5.1 supports the execution of multiple statements specified in a single query string. To use this capability with a given connection, you must specify the CLIENT_MULTI_STATEMENTS option in the flags parameter to mysql_real_connect() when opening the connection. You can also set this for an existing connection by calling mysql_set_server_option(MYSQL_OPTION_MULTI_STATEMENTS_ON).

By default, mysql_query() and mysql_real_query() return only the first query status and the subsequent queries status can be processed using mysql_more_results() and mysql_next_result().

If you enable multiple-statement support, you should process the results from mysql_query() and mysql_real_query() within a loop that checks for more results. This is true even for statements such as DROP TABLE that return a result but not a result set. Failure to process the result this way may result in a dropped connection to the server.

/* Connect to server with option CLIENT_MULTI_STATEMENTS */
mysql_real_connect(..., CLIENT_MULTI_STATEMENTS);

/* Now execute multiple queries */
mysql_query(mysql,"DROP TABLE IF EXISTS test_table;\
                   CREATE TABLE test_table(id INT);\
                   INSERT INTO test_table VALUES(10);\
                   UPDATE test_table SET id=20 WHERE id=10;\
                   SELECT * FROM test_table;\
                   DROP TABLE test_table");
do
{
  /* Process all results */
  ...
  printf("total affected rows: %lld", mysql_affected_rows(mysql));
  ...
  if (!(result= mysql_store_result(mysql)))
  {
     printf(stderr, "Got fatal error processing query\n");
     exit(1);
  }
  process_result_set(result); /* client function */
  mysql_free_result(result);
} while (!mysql_next_result(mysql));

The multiple-statement capability can be used with mysql_query() or mysql_real_query(). It cannot be used with the prepared statement interface. Prepared statement handles are defined to work only with strings that contain a single statement.

24.2.10. C API Handling of Date and Time Values

The binary protocol allows you to send and receive date and time values (DATE, TIME, DATETIME, and TIMESTAMP), using the MYSQL_TIME structure. The members of this structure are described in Section 24.2.5, “C API Prepared Statement Data types”.

To send temporal data values, create a prepared statement using mysql_stmt_prepare(). Then, before calling mysql_stmt_execute() to execute the statement, use the following procedure to set up each temporal parameter:

  1. In the MYSQL_BIND structure associated with the data value, set the buffer_type member to the type that indicates what kind of temporal value you're sending. For DATE, TIME, DATETIME, or TIMESTAMP values, set buffer_type to MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, respectively.

  2. Set the buffer member of the MYSQL_BIND structure to the address of the MYSQL_TIME structure in which you pass the temporal value.

  3. Fill in the members of the MYSQL_TIME structure that are appropriate for the type of temporal value to be passed.

Use mysql_stmt_bind_param() to bind the parameter data to the statement. Then you can call mysql_stmt_execute().

To retrieve temporal values, the procedure is similar, except that you set the buffer_type member to the type of value you expect to receive, and the buffer member to the address of a MYSQL_TIME structure into which the returned value should be placed. Use mysql_bind_results() to bind the buffers to the statement after calling mysql_stmt_execute() and before fetching the results.

Here is a simple example that inserts DATE, TIME, and TIMESTAMP data. The mysql variable is assumed to be a valid connection handle.

  MYSQL_TIME  ts;
  MYSQL_BIND  bind[3];
  MYSQL_STMT  *stmt;

  strmov(query, "INSERT INTO test_table(date_field, time_field, \
                               timestamp_field) VALUES(?,?,?");

  stmt = mysql_stmt_init(mysql);
  if (!stmt)
  {
    fprintf(stderr, " mysql_stmt_init(), out of memory\n");
    exit(0);
  }
  if (mysql_stmt_prepare(mysql, query, strlen(query)))
  {
    fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  }

  /* set up input buffers for all 3 parameters */
  bind[0].buffer_type= MYSQL_TYPE_DATE;
  bind[0].buffer= (char *)&ts;
  bind[0].is_null= 0;
  bind[0].length= 0;
  ...
  bind[1]= bind[2]= bind[0];
  ...

  mysql_stmt_bind_param(stmt, bind);

  /* supply the data to be sent in the ts structure */
  ts.year= 2002;
  ts.month= 02;
  ts.day= 03;

  ts.hour= 10;
  ts.minute= 45;
  ts.second= 20;

  mysql_stmt_execute(stmt);
  ..

24.2.11. C API Threaded Function Descriptions

You need to use the following functions when you want to create a threaded client. See Section 24.2.15, “How to Make a Threaded Client”.

24.2.11.1. my_init()

void my_init(void)

Description

This function needs to be called once in the program before calling any MySQL function. This initializes some global variables that MySQL needs. If you are using a thread-safe client library, this also calls mysql_thread_init() for this thread.

This is automatically called by mysql_init(), mysql_library_init(), mysql_server_init() and mysql_connect().

Return Values

None.

24.2.11.2. mysql_thread_init()

my_bool mysql_thread_init(void)

Description

This function needs to be called for each created thread to initialize thread-specific variables.

This is automatically called by my_init() and mysql_connect().

Return Values

Zero if successful. Non-zero if an error occurred.

24.2.11.3. mysql_thread_end()

void mysql_thread_end(void)

Description

This function needs to be called before calling pthread_exit() to free memory allocated by mysql_thread_init().

Note that this function is not invoked automatically by the client library. It must be called explicitly to avoid a memory leak.

Return Values

None.

24.2.11.4. mysql_thread_safe()

unsigned int mysql_thread_safe(void)

Description

This function indicates whether the client is compiled as thread-safe.

Return Values

1 if the client is thread-safe, 0 otherwise.

24.2.12. C API Embedded Server Function Descriptions

If you want to allow your application to be linked against the embedded MySQL server library, you must use the mysql_server_init() and mysql_server_end() functions. See Section 24.1, “libmysqld, the Embedded MySQL Server Library”.

However, to provide improved memory management, even programs that are linked with -lmysqlclient rather than -lmysqld should include calls to begin and end use of the library. The mysql_library_init() and mysql_library_end() functions can be used to do this. These actually are #define symbols that make them equivalent to mysql_server_init() and mysql_server_end(), but the names more clearly indicate that they should be called when beginning and ending use of a MySQL C API library no matter whether the application uses libmysqlclient or libmysqld. For more information, see Section 24.2.2, “C API Function Overview”.

24.2.12.1. mysql_server_init()

int mysql_server_init(int argc, char **argv, char **groups)

Description

This function must be called once in the program using the embedded server before calling any other MySQL function. It starts the server and initializes any subsystems (mysys, InnoDB, and so forth) that the server uses. If this function is not called, the next call to mysql_init() executes mysql_server_init().

In a non-multi-threaded environment, the call to mysql_server_init() may be omitted, because mysql_init() will invoke it automatically as necessary. However, a race condition is possible if mysql_server_init() is invoked by mysql_init() in a multi-threaded environment: mysql_server_init() is not thread-safe, so it should be called prior to any other client library call.

If you are using the DBUG package that comes with MySQL, you should call mysql_server_init() after you have called my_init().

The argc and argv arguments are analogous to the arguments to main(). The first element of argv is ignored (it typically contains the program name). For convenience, argc may be 0 (zero) if there are no command-line arguments for the server. mysql_server_init() makes a copy of the arguments so it's safe to destroy argv or groups after the call.

If you want to connect to an external server without starting the embedded server, you have to specify a negative value for argc.

The NULL-terminated list of strings in groups selects which groups in the option files are active. See Section 4.3.2, “Using Option Files”. For convenience, groups may be NULL, in which case the [server] and [embedded] groups are active.

Example

#include <mysql.h>
#include <stdlib.h>

static char *server_args[] = {
  "this_program",       /* this string is not used */
  "--datadir=.",
  "--key_buffer_size=32M"
};
static char *server_groups[] = {
  "embedded",
  "server",
  "this_program_SERVER",
  (char *)NULL
};

int main(void) {
  if (mysql_server_init(sizeof(server_args) / sizeof(char *),
                        server_args, server_groups))
    exit(1);

  /* Use any MySQL API functions here */

  mysql_server_end();

  return EXIT_SUCCESS;
}

Return Values

0 if okay, 1 if an error occurred.

24.2.12.2. mysql_server_end()

void mysql_server_end(void)

Description

This function must be called once in the program after all other MySQL functions. It shuts down the embedded server.

Return Values

None.

24.2.13. Common Questions and Problems When Using the C API

24.2.13.1. Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success

It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred:

  • There was a malloc() failure (for example, if the result set was too large).

  • The data couldn't be read (an error occurred on the connection).

  • The query returned no data (for example, it was an INSERT, UPDATE, or DELETE).

You can always check whether the statement should have produced a non-empty result by calling mysql_field_count(). If mysql_field_count() returns zero, the result is empty and the last query was a statement that does not return values (for example, an INSERT or a DELETE). If mysql_field_count() returns a non-zero value, the statement should have produced a non-empty result. See the description of the mysql_field_count() function for an example.

You can test for an error by calling mysql_error() or mysql_errno().

24.2.13.2. What Results You Can Get from a Query

In addition to the result set returned by a query, you can also get the following information:

  • mysql_affected_rows() returns the number of rows affected by the last query when doing an INSERT, UPDATE, or DELETE.

    For a fast re-create, use TRUNCATE TABLE.

  • mysql_num_rows() returns the number of rows in a result set. With mysql_store_result(), mysql_num_rows() may be called as soon as mysql_store_result() returns. With mysql_use_result(), mysql_num_rows() may be called only after you have fetched all the rows with mysql_fetch_row().

  • mysql_insert_id() returns the ID generated by the last query that inserted a row into a table with an AUTO_INCREMENT index. See Section 24.2.3.37, “mysql_insert_id().

  • Some queries (LOAD DATA INFILE ..., INSERT INTO ... SELECT ..., UPDATE) return additional information. The result is returned by mysql_info(). See the description for mysql_info() for the format of the string that it returns. mysql_info() returns a NULL pointer if there is no additional information.

24.2.13.3. How to Get the Unique ID for the Last Inserted Row

If you insert a record into a table that contains an AUTO_INCREMENT column, you can obtain the value stored into that column by calling the mysql_insert_id() function.

You can check from your C applications whether a value was stored in an AUTO_INCREMENT column by executing the following code (which assumes that you've checked that the statement succeeded). It determines whether the query was an INSERT with an AUTO_INCREMENT index:

if ((result = mysql_store_result(&mysql)) == 0 &&
    mysql_field_count(&mysql) == 0 &&
    mysql_insert_id(&mysql) != 0)
{
    used_id = mysql_insert_id(&mysql);
}

For more information, see Section 24.2.3.37, “mysql_insert_id().

When a new AUTO_INCREMENT value has been generated, you can also obtain it by executing a SELECT LAST_INSERT_ID() statement with mysql_query() and retrieving the value from the result set returned by the statement.

For LAST_INSERT_ID(), the most recently generated ID is maintained in the server on a per-connection basis. It is not changed by another client. It is not even changed if you update another AUTO_INCREMENT column with a non-magic value (that is, a value that is not NULL and not 0).

If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:

INSERT INTO foo (auto,text)
    VALUES(NULL,'text');         # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
    VALUES(LAST_INSERT_ID(),'text');  # use ID in second table

Note that mysql_insert_id() returns the value stored into an AUTO_INCREMENT column, whether that value is automatically generated by storing NULL or 0 or was specified as an explicit value. LAST_INSERT_ID() returns only automatically generated AUTO_INCREMENT values. If you store an explicit value other than NULL or 0, it does not affect the value returned by LAST_INSERT_ID().

24.2.13.4. Problems Linking with the C API

When linking with the C API, the following errors may occur on some systems:

gcc -g -o client test.o -L/usr/local/lib/mysql \
                        -lmysqlclient -lsocket -lnsl

Undefined        first referenced
 symbol          in file
floor            /usr/local/lib/mysql/libmysqlclient.a(password.o)
ld: fatal: Symbol referencing errors. No output written to client

If this happens on your system, you must include the math library by adding -lm to the end of the compile/link line.

24.2.14. Building Client Programs

If you compile MySQL clients that you've written yourself or that you obtain from a third-party, they must be linked using the -lmysqlclient -lz options in the link command. You may also need to specify a -L option to tell the linker where to find the library. For example, if the library is installed in /usr/local/mysql/lib, use -L/usr/local/mysql/lib -lmysqlclient -lz in the link command.

For clients that use MySQL header files, you may need to specify an -I option when you compile them (for example, -I/usr/local/mysql/include), so that the compiler can find the header files.

To make it simpler to compile MySQL programs on Unix, we have provided the mysql_config script for you. See Section 24.9.2, “mysql_config — Get Compile Options for Compiling Clients”.

You can use it to compile a MySQL client as follows:

CFG=/usr/local/mysql/bin/mysql_config
sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"

The sh -c is needed to get the shell not to treat the output from mysql_config as one word.

24.2.15. How to Make a Threaded Client

The client library is almost thread-safe. The biggest problem is that the subroutines in net.c that read from sockets are not interrupt safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. If you install interrupt handlers for the SIGPIPE interrupt, the socket handling should be thread-safe.

To avoid aborting the program when a connection terminates, MySQL blocks SIGPIPE on the first call to mysql_server_init(), mysql_init(), or mysql_connect(). If you want to use your own SIGPIPE handler, you should first call mysql_server_init() and then install your handler.

In the older binaries we distribute on our Web site (http://www.mysql.com/), the client libraries are not normally compiled with the thread-safe option (the Windows binaries are by default compiled to be thread-safe). Newer binary distributions should have both a normal and a thread-safe client library.

To get a threaded client where you can interrupt the client from other threads and set timeouts when talking with the MySQL server, you should use the -lmysys, -lmystrings, and -ldbug libraries and the net_serv.o code that the server uses.

If you don't need interrupts or timeouts, you can just compile a thread-safe client library (mysqlclient_r) and use this. See Section 24.2, “MySQL C API”. In this case, you don't have to worry about the net_serv.o object file or the other MySQL libraries.

When using a threaded client and you want to use timeouts and interrupts, you can make great use of the routines in the thr_alarm.c file. If you are using routines from the mysys library, the only thing you must remember is to call my_init() first! See Section 24.2.11, “C API Threaded Function Descriptions”.

All functions except mysql_real_connect() are by default thread-safe. The following notes describe how to compile a thread-safe client library and use it in a thread-safe manner. (The notes below for mysql_real_connect() actually apply to mysql_connect() as well, but because mysql_connect() is deprecated, you should be using mysql_real_connect() anyway.)

To make mysql_real_connect() thread-safe, you must recompile the client library with this command:

shell> ./configure --enable-thread-safe-client

This creates a thread-safe client library libmysqlclient_r. (Assuming that your OS has a thread-safe gethostbyname_r() function.) This library is thread-safe per connection. You can let two threads share the same connection with the following caveats:

  • Two threads can't send a query to the MySQL server at the same time on the same connection. In particular, you have to ensure that between a mysql_query() and mysql_store_result() no other thread is using the same connection.

  • Many threads can access different result sets that are retrieved with mysql_store_result().

  • If you use mysql_use_result, you have to ensure that no other thread is using the same connection until the result set is closed. However, it really is best for threaded clients that share the same connection to use mysql_store_result().

  • If you want to use multiple threads on the same connection, you must have a mutex lock around your mysql_query() and mysql_store_result() call combination. Once mysql_store_result() is ready, the lock can be released and other threads may query the same connection.

  • If you program with POSIX threads, you can use pthread_mutex_lock() and pthread_mutex_unlock() to establish and release a mutex lock.

You need to know the following if you have a thread that is calling MySQL functions which did not create the connection to the MySQL database:

When you call mysql_init() or mysql_connect(), MySQL creates a thread-specific variable for the thread that is used by the debug library (among other things).

If you call a MySQL function, before the thread has called mysql_init() or mysql_connect(), the thread does not have the necessary thread-specific variables in place and you are likely to end up with a core dump sooner or later.

To get things to work smoothly you have to do the following:

  1. Call my_init() at the start of your program if it calls any other MySQL function before calling mysql_real_connect().

  2. Call mysql_thread_init() in the thread handler before calling any MySQL function.

  3. In the thread, call mysql_thread_end() before calling pthread_exit(). This frees the memory used by MySQL thread-specific variables.

You may get some errors because of undefined symbols when linking your client with libmysqlclient_r. In most cases this is because you haven't included the thread libraries on the link/compile line.

24.3. MySQL PHP API

PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic Web pages. It is available for most operating systems and Web servers, and can access most common databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache Web server.

PHP actually provides two different MySQL API extensions:

  • mysql: Available for PHP versions 4 and 5, this extension is intended for use with MySQL versions prior to MySQL 4.1. This extension does not support the improved authentication protocol used in MySQL 5.1, nor does it support prepared statements or multiple statements. If you wish to use this extension with MySQL 5.1, you will likely want to configure the MySQL server to use the --old-passwords option (see Section B.2.3, “Client does not support authentication protocol). This extension is documented on the PHP Web site at http://php.net/mysql.

  • mysqli - Stands for “MySQL, Improved”; this extension is available only in PHP 5. It is intended for use with MySQL 4.1.1 and later. This extension fully supports the authentication protocol used in MySQL 5.1, as well as the Prepared Statements and Multiple Statements APIs. In addition, this extension provides an advanced, object-oriented programming interface. You can read the documentation for the mysqli extension at http://php.net/mysqli. A helpful article can be found at http://www.zend.com/php5/articles/php5-mysqli.php.

If you're experiencing problems with enabling both the mysql and the mysqli extension when building PHP on Linux yourself, see Section 24.3.2, “Enabling Both mysql and mysqli in PHP”.

The PHP distribution and documentation are available from the PHP Web site. MySQL provides the mysql and mysqli extensions for the Windows operating system on http://dev.mysql.com/downloads/connector/php/. You can find information why you should preferably use the extensions provided by MySQL on that page.

24.3.1. Common Problems with MySQL and PHP

  • Error: Maximum Execution Time Exceeded: This is a PHP limit; go into the php.ini file and set the maximum execution time up from 30 seconds to something higher, as needed. It is also not a bad idea to double the RAM allowed per script to 16MB instead of 8MB.

  • Fatal error: Call to unsupported or undefined function mysql_connect() in ...: This means that your PHP version isn't compiled with MySQL support. You can either compile a dynamic MySQL module and load it into PHP or recompile PHP with built-in MySQL support. This process is described in detail in the PHP manual.

  • Error: Undefined reference to 'uncompress': This means that the client library is compiled with support for a compressed client/server protocol. The fix is to add -lz last when linking with -lmysqlclient.

  • Error: Client does not support authentication protocol: This is most often encountered when trying to use the older mysql extension with MySQL 4.1.1 and later. Possible solutions are: downgrade to MySQL 4.0; switch to PHP 5 and the newer mysqli extension; or configure the MySQL server with --old-passwords. (See Section B.2.3, “Client does not support authentication protocol, for more information.)

Those with PHP4 legacy code can make use of a compatibility layer for the old and new MySQL libraries, such as this one: http://www.coggeshall.org/oss/mysql2i.

24.3.2. Enabling Both mysql and mysqli in PHP

If you're experiencing problems with enabling both the mysql and the mysqli extension when building PHP on Linux yourself, you should try the following procedure.

  1. Configure PHP like this:

    ./configure --with-mysqli=/usr/bin/mysql_config --with-mysql=/usr  
    

  2. Edit the Makefile and search for a line that starts with EXTRA_LIBS. It might look like this (all on one line):

    EXTRA_LIBS = -lcrypt -lcrypt -lmysqlclient -lz -lresolv -lm -ldl -lnsl
    -lxml2 -lz -lm -lxml2 -lz -lm -lmysqlclient -lz -lcrypt -lnsl -lm
    -lxml2 -lz -lm -lcrypt -lxml2 -lz -lm -lcrypt
    

    Remove all duplicates, so that the line looks like this (all on one line):

    EXTRA_LIBS = -lcrypt -lcrypt -lmysqlclient -lz -lresolv -lm -ldl -lnsl
    -lxml2
    

  3. Build and install PHP:

    make
    make install
    

24.4. MySQL Perl API

The Perl DBI module provides a generic interface for database access. You can write a DBI script that works with many different database engines without change. To use DBI, you must install the DBI module, as well as a DataBase Driver (DBD) module for each type of server you want to access. For MySQL, this driver is the DBD::mysql module.

Perl DBI is the recommended Perl interface. It replaces an older interface called mysqlperl, which should be considered obsolete.

Installation instructions for Perl DBI support are given in Section 2.14, “Perl Installation Notes”.

DBI information is available at the command line, online, or in printed form:

  • Once you have the DBI and DBD::mysql modules installed, you can get information about them at the command line with the perldoc command:

    shell> perldoc DBI
    shell> perldoc DBI::FAQ
    shell> perldoc DBD::mysql
    

    You can also use pod2man, pod2html, and so forth to translate this information into other formats.

  • For online information about Perl DBI, visit the DBI Web site, http://dbi.perl.org/. That site hosts a general DBI mailing list. MySQL AB hosts a list specifically about DBD::mysql; see Section 1.7.1, “MySQL Mailing Lists”.

  • For printed information, the official DBI book is Programming the Perl DBI (Alligator Descartes and Tim Bunce, O'Reilly & Associates, 2000). Information about the book is available at the DBI Web site, http://dbi.perl.org/.

    For information that focuses specifically on using DBI with MySQL, see MySQL and Perl for the Web (Paul DuBois, New Riders, 2001). This book's Web site is http://www.kitebird.com/mysql-perl/.

24.5. MySQL C++ API

MySQL++ is a MySQL API for C++. Warren Young has taken over this project. More information can be found at http://www.mysql.com/products/mysql++/.

24.6. MySQL Python API

MySQLdb provides MySQL support for Python, compliant with the Python DB API version 2.0. It can be found at http://sourceforge.net/projects/mysql-python/.

24.7. MySQL Tcl API

MySQLtcl is a simple API for accessing a MySQL database server from the Tcl programming language. It can be found at http://www.xdobry.de/mysqltcl/.

24.8. MySQL Eiffel Wrapper

Eiffel MySQL is an interface to the MySQL database server using the Eiffel programming language, written by Michael Ravits. It can be found at http://efsa.sourceforge.net/archive/ravits/mysql.htm.

24.9. MySQL Program Development Utilities

This section describes some utilities that you may find useful when developing MySQL programs.

  • msql2mysql

    A shell script that converts mSQL programs to MySQL. It doesn't handle every case, but it gives a good start when converting.

  • mysql_config

    A shell script that produces the option values needed when compiling MySQL programs.

24.9.1. msql2mysql — Convert mSQL Programs for Use with MySQL

Initially, the MySQL C API was developed to be very similar to that for the mSQL database system. Because of this, mSQL programs often can be converted relatively easily for use with MySQL by changing the names of the C API functions.

The msql2mysql utility performs the conversion of mSQL C API function calls to their MySQL equivalents. msql2mysql converts the input file in place, so make a copy of the original before converting it. For example, use msql2mysql like this:

shell> cp client-prog.c client-prog.c.orig
shell> msql2mysql client-prog.c
client-prog.c converted

Then examine client-prog.c and make any post-conversion revisions that may be necessary.

msql2mysql uses the replace utility to make the function name substitutions. See Section 8.19, “replace — A String-Replacement Utility”.

24.9.2. mysql_config — Get Compile Options for Compiling Clients

mysql_config provides you with useful information for compiling your MySQL client and connecting it to MySQL.

mysql_config supports the following options:

  • --cflags

    Compiler flags to find include files and critical compiler flags and defines used when compiling the libmysqlclient library.

  • --include

    Compiler options to find MySQL include files. (Note that normally you would use --cflags instead of this option.)

  • --libmysqld-libs, --embedded

    Libraries and options required to link with the MySQL embedded server.

  • --libs

    Libraries and options required to link with the MySQL client library.

  • --libs_r

    Libraries and options required to link with the thread-safe MySQL client library.

  • --port

    The default TCP/IP port number, defined when configuring MySQL.

  • --socket

    The default Unix socket file, defined when configuring MySQL.

  • --version

    Version number for the MySQL distribution.

If you invoke mysql_config with no options, it displays a list of all options that it supports, and their values:

shell> mysql_config
Usage: /usr/local/mysql/bin/mysql_config [options]
Options:
  --cflags         [-I/usr/local/mysql/include/mysql -mcpu=pentiumpro]
  --include        [-I/usr/local/mysql/include/mysql]
  --libs           [-L/usr/local/mysql/lib/mysql -lmysqlclient -lz
                    -lcrypt -lnsl -lm -L/usr/lib -lssl -lcrypto]
  --libs_r         [-L/usr/local/mysql/lib/mysql -lmysqlclient_r
                    -lpthread -lz -lcrypt -lnsl -lm -lpthread]
  --socket         [/tmp/mysql.sock]
  --port           [3306]
  --version        [4.0.16]
  --libmysqld-libs [-L/usr/local/mysql/lib/mysql -lmysqld -lpthread -lz
                    -lcrypt -lnsl -lm -lpthread -lrt]

You can use mysql_config within a command line to include the value that it displays for a particular option. For example, to compile a MySQL client program, use mysql_config as follows:

shell> CFG=/usr/local/mysql/bin/mysql_config
shell> sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"

When you use mysql_config this way, be sure to invoke it within backtick (‘`’) characters. That tells the shell to execute it and substitute its output into the surrounding command.