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) 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 Section 4.8, “MySQL Client-Side Scripts and Utilities ”, for a list of these variables.
The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16K bytes) is automatically increased up to the maximum size (the maximum is 16M). 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 queries 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 16M of data, you must have a communication buffer limit of at least 16M (in both server and client). The client's default maximum is 16M, but the default maximum in the server is 1M. You can increase this by changing the value of the max_allowed_packet parameter when the server is started. Section 5.5.2, “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 9.1.14, “How to Make a Threaded Client ”. For creating a stand-alone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see Section 9.1.15, “libmysqld, the Embedded MySQL Server Library ”.
This structure represents a handle to one database connection. It is used for almost all MySQL functions.
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.
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().
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.
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.
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 will 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));
The MYSQL_FIELD structure contains the members listed here:
The name of the field, as a null-terminated string.
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.
The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields().
The type of the field. The type value may be one of the following:
| Type value | Type description |
| FIELD_TYPE_TINY | TINYINT field |
| FIELD_TYPE_SHORT | SMALLINT field |
| FIELD_TYPE_LONG | INTEGER field |
| FIELD_TYPE_INT24 | MEDIUMINT field |
| FIELD_TYPE_LONGLONG | BIGINT field |
| FIELD_TYPE_DECIMAL | DECIMAL or NUMERIC field |
| FIELD_TYPE_FLOAT | FLOAT field |
| FIELD_TYPE_DOUBLE | DOUBLE or REAL field |
| FIELD_TYPE_TIMESTAMP | TIMESTAMP field |
| FIELD_TYPE_DATE | DATE field |
| FIELD_TYPE_TIME | TIME field |
| FIELD_TYPE_DATETIME | DATETIME field |
| FIELD_TYPE_YEAR | YEAR field |
| FIELD_TYPE_STRING | CHAR field |
| FIELD_TYPE_VAR_STRING | VARCHAR field |
| FIELD_TYPE_BLOB | BLOB or TEXT field (use max_length to determine the maximum length) |
| FIELD_TYPE_SET | SET field |
| FIELD_TYPE_ENUM | ENUM field |
| FIELD_TYPE_NULL | NULL-type field |
| FIELD_TYPE_CHAR | Deprecated; use FIELD_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 will evaluate to TRUE if the field is numeric:
if (IS_NUM(field-type))
printf("Field is numeric\n");
The width of the field, as specified in the table definition.
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.
Different bit-flags for the field. The flags value may have zero or more of the following bits set:
| Flag value | Flag description |
| NOT_NULL_FLAG | Field can't be NULL |
| PRI_KEY_FLAG | Field is part of a primary key |
| UNIQUE_KEY_FLAG | Field is part of a unique key |
| MULTIPLE_KEY_FLAG | Field is part of a non-unique key |
| UNSIGNED_FLAG | Field has the UNSIGNED attribute |
| ZEROFILL_FLAG | Field has the ZEROFILL attribute |
| BINARY_FLAG | Field has the BINARY attribute |
| AUTO_INCREMENT_FLAG | Field has the AUTO_INCREMENT attribute |
| ENUM_FLAG | Field is an ENUM (deprecated) |
| SET_FLAG | Field is a SET (deprecated) |
| BLOB_FLAG | Field is a BLOB or TEXT (deprecated) |
| TIMESTAMP_FLAG | Field 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 FIELD_TYPE_BLOB, FIELD_TYPE_ENUM, FIELD_TYPE_SET, or FIELD_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 status | Description |
| 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) |
The number of decimals for numeric fields.
The functions available in the C API are summarised here and described in greater detail in a later section. Section 9.1.3, “C API Function Descriptions ”.
| Function | Description |
| mysql_affected_rows() | Returns the number of rows changed/deleted/inserted by the last UPDATE, DELETE, or INSERT query. |
| mysql_change_user() | Changes user and database on an open connection. |
| mysql_character_set_name() | Returns the name of the default character set for the connection. |
| mysql_close() | Closes a server connection. |
| 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 command 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 command 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 query. |
| 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. |
| mysql_get_host_info() | Returns a string describing the connection. |
| mysql_get_server_version() | Returns version number of server as an integer (new in 4.1). |
| 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 initialises 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_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_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 charset of the connection. |
| mysql_real_query() | Executes an SQL query specified as a counted string. |
| mysql_reload() | Tells the server to reload the grant tables. |
| 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_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_commit() | Commits the transaction (new in 4.1). |
| mysql_rollback() | Rolls back the transaction (new in 4.1). |
| mysql_autocommit() | Toggles autocommit mode on/off (new in 4.1). |
| mysql_more_results() | Checks whether any more results exist (new in 4.1). |
| mysql_next_result() | Returns/Initiates the next result in multi-query executions (new in 4.1). |
To connect to the server, call mysql_init() to initialise a connection handler, then call mysql_real_connect() with that handler (along with other information such as the hostname, user name, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up. When you are done with the connection, call mysql_close() to terminate it.
While a connection is active, the client may send SQL queries 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 initialises 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 already 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 queries (retrieving rows only as necessary) without knowing whether or not the query 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 query 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 query returned no data (indicating that it was an INSERT, UPDATE, DELETE, etc.), and was not expected to return rows. If mysql_field_count() is non-zero, the query should have returned rows, but didn't. This indicates that the query 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, etc.). 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.
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().
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().
An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records where 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().
mysql_query(mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%ld products updated",(long) mysql_affected_rows(mysql));
If one specifies the flag CLIENT_FOUND_ROWS when connecting to mysqld, mysql_affected_rows() will return the number of rows matched by the WHERE statement for UPDATE statements.
Note that when one uses a REPLACE command, mysql_affected_rows() will return 2 if the new row replaced and old row. This is because in this case one row was inserted after the duplicate was deleted.
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.
This function was introduced in MySQL Version 3.23.3.
mysql_change_user() fails unless the connected user can be authenticated or if he 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.
Starting from MySQL 4.0.6 this command will always ROLLBACK any active transactions, close all temporary tables, unlock all locked tables and reset the state as if one had done a new connect. This will happen even if the user didn't change.
The same that you can get from mysql_real_connect().
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
The MySQL server doesn't implement this command (probably an old server).
The user or password was wrong.
The database didn't exist.
The user did not have access rights to the database.
The database name was too long.
if (mysql_change_user(mysql, "user", "password", "new_database"))
{
fprintf(stderr, "Failed to change user. Error: %s\n",
mysql_error(mysql));
}
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().
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.)
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.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
if(mysql_create_db(mysql, "my_database"))
{
fprintf(stderr, "Failed to create new database. Error: %s\n",
mysql_error(mysql));
}
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(stmt)-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().
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. Section E.1, “Debugging a MySQL server ”. Section E.2, “Debugging a MySQL client ”.
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");
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.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
if(mysql_drop_db(mysql, "my_database"))
fprintf(stderr, "Failed to drop the database: Error: %s\n",
mysql_error(mysql));
Instructs the server to write some debug information to the log. For this to work, the connected user must have the SUPER privilege.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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() will always return 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 now 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.)
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));
}
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. In the MySQL source distribution you can find a complete list of error messages and error numbers in the file Docs/mysqld_error.txt. The server error codes also are listed at Section 10.1, “Error Returns ”.
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 will reset mysql_errno() if they succeed.
An error code value for the last mysql_xxx call, if it failed. zero means no error occurred.
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 will reset mysql_error() if they succeed.
For functions that resets mysql_errno, the following two tests are equivalent:
if(mysql_errno(mysql))
{
// an error occurred
}
if(mysql_error(mysql)[0] != '\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. Section 4.6.2, “Non-English Error Messages ”.
A null-terminated character string that describes the error. An empty string if no error occurred.
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 charset setting.
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 (8K bytes) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8K 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.
MYSQL_FIELD *field;
while((field = mysql_fetch_field(result)))
{
printf("field name %s\n", field-name);
}
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.
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);
}
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.
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);
}
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 optimisation, 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().
An array of unsigned long integers representing the size of each column (not including any terminating null characters). NULL if an error occurred.
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.
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]);
}
}
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.
A MYSQL_ROW structure for the next row. NULL if there are no more rows to retrieve or if an error occurred.
Note that error is not reset between calls to mysql_fetch_row()
The connection to the server was lost during the query.
An unknown error occurred.
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");
}
unsigned int mysql_field_count(MYSQL *mysql)
If you are using a version of MySQL earlier than Version 3.22.24, you should use unsigned int mysql_num_fields(MYSQL *mysql) instead.
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.
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.
Sets the field cursor to the given offset. The next call to mysql_fetch_field() will retrieve the field definition of the column associated with that offset.
To seek to the beginning of a row, pass an offset value of zero.
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().
Frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), etc. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().
A number that represents the MySQL server version in format:
main_version*10000 + minor_version *100 + sub_version
For example, 4.1.0 is returned as 40100.
This is useful to quickly determine the version of the server in a client program to know if some capability exits.
Returns a string describing the type of connection in use, including the server host name.
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 will contain values appropriate for the query.
String format: Records: 100 Duplicates: 0 Warnings: 0
String format: Records: 3 Duplicates: 0 Warnings: 0
String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
String format: Records: 3 Duplicates: 0 Warnings: 0
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).
A character string representing additional information about the most recently executed query. NULL if no information is available for the query.
Allocates or initialises a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initialises, and returns a new object. Otherwise, the object is initialised and the address of the object is returned. If mysql_init() allocates a new object, it will be freed when mysql_close() is called to close the connection.
An initialised MYSQL* handle. NULL if there was insufficient memory to allocate a new object.
Returns the ID generated for an AUTO_INCREMENT column by the previous query. Use this function after you have performed an INSERT query into a table that contains an AUTO_INCREMENT field.
Note that mysql_insert_id() returns 0 if the previous query does not generate an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the query that generates the value.
If the previous query returned an error, the value of mysql_insert_id() is undefined.
mysql_insert_id() is updated after INSERT and UPDATE statements that generate an AUTO_INCREMENT value or that set a column value to LAST_INSERT_ID(expr). Section 6.3.6.2, “Miscellaneous Functions ”.
Also note that the value of the SQL LAST_INSERT_ID() function always contains the most recently generated AUTO_INCREMENT value, and is not reset between queries because the value of that function is maintained in the server.
The value of the AUTO_INCREMENT field that was updated by the previous query. Returns zero if there was no previous query on the connection or if the query did not update an AUTO_INCREMENT value.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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().
Commands were executed in an improper order.
Out of memory.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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().
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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().
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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().
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
unsigned int mysql_num_fields(MYSQL_RES *result)
or
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a MYSQL* argument, you must use unsigned int mysql_field_count(MYSQL *mysql) instead.
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 or not the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.
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 if mysql_field_count(mysql) is = 0. This will only happen if something went wrong.
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() will not return the correct value until all the rows in the result set have been retrieved.
Can be used to set extra connect options and affect behaviour 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 options values:
| Option | Argument type | Function |
| MYSQL_OPT_CONNECT_TIMEOUT | unsigned int * | Connect timeout in seconds. |
| MYSQL_OPT_COMPRESS | Not used | Use the compressed client/server protocol. |
| MYSQL_OPT_LOCAL_INFILE | optional pointer to uint | If no pointer is given or if pointer points to an unsigned int != 0 the command LOAD LOCAL INFILE is enabled. |
| MYSQL_OPT_NAMED_PIPE | Not used | Use named pipes to connect to a MySQL server on NT. |
| MYSQL_INIT_COMMAND | char * | Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting. |
| MYSQL_READ_DEFAULT_FILE | char * | Read options from the named option file instead of from my.cnf. |
| MYSQL_READ_DEFAULT_GROUP | char * | Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE. |
Note that the group client 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:
| Option | Description |
| connect-timeout | Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server. |
| compress | Use the compressed client/server protocol. |
| database | Connect to this database if no database was specified in the connect command. |
| debug | Debug options. |
| disable-local-infile | Disable use of LOAD DATA LOCAL. |
| host | Default host name. |
| init-command | Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting. |
| interactive-timeout | Same as specifying CLIENT_INTERACTIVE to mysql_real_connect(). Section 9.1.3.42, “mysql_real_connect()”. |
| local-infile[=(0|1)] | If no argument or argument != 0 then enable use of LOAD DATA LOCAL. |
| max_allowed_packet | Max size of packet client can read from server. |
| password | Default password. |
| pipe | Use named pipes to connect to a MySQL server on NT. |
| protocol=(TCP | SOCKET | PIPE | MEMORY) | Which protocol to use when connecting to server (New in 4.1) |
| port | Default port number. |
| return-found-rows | Tell mysql_info() to return found rows instead of updated rows when using UPDATE. |
| shared-memory-base-name=name | Shared memory name to use to connect to server (default is "MySQL"). New in MySQL 4.1. |
| socket | Default socket number. |
| user | Default user. |
Note that timeout has been replaced by connect-timeout, but timeout will still work for a while.
For more information about option files, see Section 4.1.2, “my.cnf Option Files ”.
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));
}
The above requests the client to use the compressed client/server protocol and read the additional options from the odbc section in the my.cnf file.
Checks whether the connection to the server is working. If it 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.
Commands were executed in an improper order.
The MySQL server has gone away.
An unknown error occurred.
Executes the SQL query pointed to by the null-terminated string query. The query must consist of a single SQL statement. You should not add a terminating semicolon (;) or \g to the statement.
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 if the query should return a result set or not, you can use mysql_field_count() to check for this. Section 9.1.3.20, “mysql_field_count()”.
Commands were executed in an improper order.
The MySQL server has gone away.
The connection to the server was lost during the query.
An unknown error occurred.
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)
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 of the other API functions, with the exception of mysql_get_client_info().
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 initialise the MYSQL structure. You can change a lot of connect options with the mysql_options() call. 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. If the OS supports sockets (Unix) or named pipes (Windows), they are used instead of TCP/IP to connect to the server.
The user parameter contains the user's MySQL login ID. If user is NULL, the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current user name must be specified explicitly. Section 9.2.2, “How to Fill in the Various Fields in the ODBC Administrator Program ”.
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 will be 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 or not 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 will set the default database to this value.
If port is not 0, the value will be 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 in very special circumstances:
| Flag name | Flag description |
| CLIENT_COMPRESS | Use compression protocol. |
| CLIENT_FOUND_ROWS | Return the number of found (matched) rows, not the number of affected rows. |
| CLIENT_IGNORE_SPACE | Allow spaces after function names. Makes all functions names reserved words. |
| CLIENT_INTERACTIVE | Allow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. |
| CLIENT_LOCAL_FILES | Enable LOAD DATA LOCAL handling. |
| CLIENT_MULTI_QUERIES | Tell the server that the client may send multi-row-queries (separated with ;). If this flag is not set, multi-row-queries are disabled. New in 4.1. |
| CLIENT_MULTI_RESULTS | Tell the server that the client can handle multiple-result sets from multi-queries or stored procedures. This is automatically set if CLIENT_MULTI_QUERIES is set. New in 4.1. |
| CLIENT_NO_SCHEMA | Don'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_ODBC | The client is an ODBC client. This changes mysqld to be more ODBC-friendly. |
| CLIENT_SSL | Use SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library. |
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.
Failed to connect to the MySQL server.
Failed to connect to the local MySQL server.
Failed to create an IP socket.
Out of memory.
Failed to create a Unix socket.
Failed to find the IP address for the hostname.
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.
Failed to create a named pipe on Windows.
Failed to wait for a named pipe on Windows.
Failed to get a pipe handler on Windows.
If connect_timeout 0 and it took longer then connect_timeout seconds to connect to the server or if the server died while executing the init-command.
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 will read the [client] and [your_prog_name] sections in the my.cnf file which will ensure that your program will work, 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. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up.
unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)
This function is used to create a legal SQL string that you can use in a SQL statement. Section 6.1.1.1, “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 (Section 6.1.1, “Literals: How to Write Strings and Numbers ”). (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 will be a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.
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 -