MySQL 中mysql_query()来判断数据库是否连接中断

最近的项目在使用mysql C API进行数据库操作时，写了一个简易的连接池，因为mysql查询和插入频繁，但是单次查询与插入的时间开销小，每次进行数据库连接时的开销大。于是进程启动时建立了若干个长连接加入到连接池中，不同的查询和插入复用这些长连接即可。但是随之会有一个问题，当进程运行了相当长一段时间后，mysql对象中可能与mysql服务器断开连接，这需要做处理。

在每次一个mysql_query时，获得返回值，通过返回值来判断是否需要重建mysql连接。

mysql_query()

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

Description

Executes the SQL statement pointed to by the null-terminated string stmt_str. Normally, the string must consist of a single SQL statement without a terminating semicolon (;) or g. If multiple-statement execution has been enabled, the string can contain several statements separated by semicolons. See Section 26.8.17, “C API Support for Multiple Statement Execution”.

mysql_query() cannot be used for statements that contain binary data; you must use mysql_real_query() instead. (Binary data may contain the  character, which mysql_query() interprets as the end of the statement string.)

If you want to know whether the statement returns a result set, you can use mysql_field_count() to check for this. See Section 26.8.7.22, “mysql_field_count()”.

Return Values

Zero for success. Nonzero 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.

因此可以通过 CR_SEVER_GONE_ERROR与CR_SERVER_LOST来判断是否需要重建连接。
注意，需要包含errmsg.h文件

#include <errmsg.h>
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flag<-mysql_query()
if flag=CR_SERVER_LOST or flag=SERVER_GONE_ERROR
        Reconnect()
        mysql_query()
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