C/C++程序中如何连接MySQL数据库？

feeling

mysql_init后，我用mysql_real_connect连接MySQL数据库，出错，提示如下：
Failed to connect to database : Can't connect to local MySQL server through socket '/tmp/mysql.sock' (146)
由于MySQL数据库是另一个用户mysql启动的，我就su到mysql用户下执行测试程序，出错，提示：
Failed to connect to database : Access denied for user 'mysql'@'localhost' (using password: NO)
奇怪，于是，我在程序代码中加上了用户口令信息，再次出错，提示如下：
Failed to connect to database : Client does not support authentication protocol requested by server; consider upgrading MySQL client

何解？