解决error：2014 Commands out of sync; you can't run this command now
用mysql C API 调用存储过程，并返回结果集。需要注意几个问题：
在建立链接的时候要加选项CLIENT_MULTI_STATEMENTS 或 CLIENT_MULTI_RESULTS，以便可以让query执行多个语句。
mysql_real_connect(mySQL,serverIP,user,password,database,serverPort,NULL,CLIENT_MULTI_STATEMENTS)
当query时可能产生错误error：2014 Commands out of sync; you can't run this command now
Mysql文档中说明错误：Commands out of sync
If you get Commands out of sync; you can't run this command now in your client code, you are calling client functions in the wrong order.
This can happen, for example, if you are using mysql_use_result() and try to execute a new query before you have called mysql_free_result(). It can also happen if you try to execute two queries that return data without calling mysql_use_result() or mysql_store_result() in between.
当执行完query后，mysql将结果集放在一个result集中，产生以上问题的原因有两个：
一是未将MYSQL_RES所指对象释放，即在下次查询时要mysql_free_result();
二是结果result集不为空，这个原因比较隐蔽。解决方法可以用如下写法：
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));
还有个问题感觉比较奇怪，我调用一个存储过程，存储过程中就一句select
Create procedure test()
Begin
Select * from test ;
End ;
用以上方法处理结果集循环会执行两次，开始我只调了一次result= mysql_store_result(mysql))，导致以后执行query报2014错误。