C api-read MySQL database content in C language on Linux

C api-read MySQL database content in C language on Linux

If you want to know how to operate databases in C language, you must understand the meanings of these structures. Here is a brief introduction. If you want to learn more deeply, you can search for them on the Internet.

C api data type

1. the MySQL structure represents a database connection handle, which contains information about the connection status of the server. Almost all functions use it. To connect to MySQL, you must create a MySQL instance and initiate the connection through MySQL_init.

2. The MySQL_RES result indicates the returned query result (select, show, etc ). The returned information is also the result set ". In the c API, MySQL_RES is used to read data from the database and MySQL_RES.

3. MySQL_ROW is a type-safe representation of row data. Currently, it is implemented as a string array that counts bytes. (If the field value may contain binary data, you cannot regard it as a null termination string because such a value can contain null bytes internally) rows are obtained by calling MySQL_fetch_row.

The functions available for c api are summarized here. For details, see the MySQL manual.

Function	Description
Mysql_affected_rows ()	Returns the number of rows modified, deleted, or inserted by the last UPDATE, DELETE, or INSERT query.
Mysql_autocommit ()	Switch autocommit mode, ON/OFF
Mysql_change_user ()	Change the user and database on the connection.
Mysql_charset_name ()	Returns the name of the default character set for connection.
Mysql_close ()	Disable the server connection.
Mysql_commit ()	Commit a transaction.
Mysql_connect ()	Connect to the MySQL server. This function is no longer valued and replaced by mysql_real_connect.
Mysql_create_db ()	Create a database. This function is no longer valued and replaced by the SQL statement CREATE DATABASE.
Mysql_data_seek ()	Search for the row number in the query result set.
Mysql_debug ()	Execute DBUG_PUSH with the given string.
Mysql_drop_db ()	Undo the database. This function is no longer valued. Instead, use the SQL statement DROP DATABASE.
Mysql_dump_debug_info ()	Allows the server to write debugging information to logs.
Mysql_eof ()	Determine whether the last row of the result set is read. This function is no longer valued. you can replace it with mysql_errno () or mysql_error.
Mysql_errno ()	Returns the error number of the MySQL function called last time.
Mysql_error ()	Returns the error message of the MySQL function called last time.
Mysql_escape_string ()	Escape special characters for use in SQL statements.
Mysql_fetch_field ()	Returns the type of the next table field.
Mysql_fetch_field_direct ()	If the field number is specified, the type of the table field is returned.
Mysql_fetch_fields ()	Returns an array of all field structures.
Mysql_fetch_lengths ()	Returns the length of all columns in the current row.
Mysql_fetch_row ()	Obtain the next row from the result set
Mysql_field_seek ()	Place the column cursor in the specified column.
Mysql_field_count ()	Returns the number of result columns of the last statement executed.
Mysql_field_tell ()	Returns the cursor position of the field used in mysql_fetch_field.
Mysql_free_result ()	Releases the memory used by the result set.
Mysql_get_client_info ()	Returns the Client Version in string format.
Mysql_get_client_version ()	Returns the Client Version Information in integer format.
Mysql_get_host_info ()	Returns the string that describes the connection.
Mysql_get_server_version ()	Returns the server version number in integer format.
Mysql_get_proto_info ()	Returns the Protocol Version Used for the connection.
Mysql_get_server_info ()	Returns the server version number.
Mysql_info ()	Returns information about the latest query.
Mysql_init ()	Obtain or initialize the MYSQL structure.
Mysql_insert_id ()	Returns the ID generated in the previous query for the AUTO_INCREMENT column.
Mysql_kill ()	Kill the specified thread.
Mysql_library_end ()	Finally, determine the MySQL c api library.
Mysql_library_init ()	Initialize the MySQL c api library.
Mysql_list_dbs ()	Returns the name of the database that matches the simple regular expression.
Mysql_list_fields ()	Returns the name of a field that matches a simple regular expression.
Mysql_list_processes ()	Returns the list of current server threads.
Mysql_list_tables ()	Returns the name of the table that matches the simple regular expression.
Mysql_more_results ()	Check whether other results exist.
Mysql_next_result ()	Return/initialize the next result during multi-statement execution.
Mysql_num_fields ()	Number of columns in the returned result set.
Mysql_num_rows ()	The number of rows in the returned result set.
Mysql_options ()	Set connection options for mysql_connect.
Mysql_ping ()	Check whether the connection to the server works and try again if necessary.
Mysql_query ()	Execute an SQL query that is specified as a string ending with Null.
Mysql_real_connect ()	Connect to the MySQL server.
Mysql_real_escape_string ()	Considering the connected Current Character Set, escape special characters in the string to be used in SQL statements.
Mysql_real_query ()	Execute the SQL query specified as the Count string.
Mysql_refresh ()	Refresh or reset the table and cache.
Mysql_reload ()	Notifies the server to load the authorization table again.
Mysql_rollback ()	Roll back the transaction.
Mysql_row_seek ()	Use the value returned from mysql_row_tell () to find the row offset in the result set.
Mysql_row_tell ()	Returns the cursor position of a row.
Mysql_select_db ()	Select a database.
Mysql_server_end ()	Finally, the Embedded Server library is determined.
Mysql_server_init ()	Initialize the Embedded Server library.
Mysql_set_server_option ()	Set options for connection (for example, multiple statements ).
Mysql_sqlstate ()	Returns the SQLSTATE error code about the previous error.
Mysql_shutdown ()	Shut down the database server.
Mysql_stat ()	Returns the server status in string format.
Mysql_store_result ()	Retrieve the complete result set to the client.
Mysql_thread_id ()	Returns the ID of the current thread.
Mysql_thread_safe ()	If the client has been compiled into thread-safe, 1 is returned.
Mysql_use_result ()	Initialize row-by-row result set retrieval.
Mysql_warning_count ()	Returns the number of alerts for the previous SQL statement.

Next, let's take a look at how to use c api to operate databases.

 

The following example shows how to read data from a database table.

# Include <stdio. h>
# Include <mysql. h>
# Include <string. h>
Int main ()
{
MYSQL mysql; // mysql connection
MYSQL_RES * res; // This structure indicates a query result set of the returned row.
MYSQL_ROW row; // type-safe representation of the data in a row
Char * query; // query statement
Int t, r;
Mysql_init (& mysql );
If (! Mysql_real_connect (& mysql, "localhost", "root", NULL, "test", 0, NULL, 0 ))
{

Printf ("Error connecting to database: % s", mysql_error (& mysql ));

}
Else
{
Printf ("Connected... \ n ");
}
Query = "select * from qq ";
T = mysql_real_query (& mysql, query, (unsigned int) strlen (query); // execute an SQL query specified as a Count string.
If (t)
{
Printf ("exception occurred during display: % s", mysql_error (& mysql ));
}
Res = mysql_store_result (& mysql); // retrieve the complete result set to the client.
Printf ("Name \ t student ID \ t age \ t \ n ");
While (row = mysql_fetch_row (res ))
{

For (t = 0; t <mysql_num_fields (res); t ++)
{
Printf ("% s \ t", row [t]);
}
Printf ("\ n ");

}
Mysql_free_result (res); // release the memory used by the result set.
Mysql_close (& mysql );
Return 0;
}

Run the following command and code:

In fact, it is very simple.

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