mysql connector c++

执行完一个语句后,第二个语句就报Commands out of sync; you can't run this command now

代码能发上来看看吗?

解决error:2014 Commands out of sync; you can't run this command now

前两天搞mysql的东西,用mysql提供的C API 访问,遇到些问题,在这里分享一下,希望对其他人有帮助。

 

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。

  在使用navcat的窗口查询mysql的数据时,一直出现
  “Commands out of sync; you can't run this command now? ”,我把sql改为最简单的 select 1,居然也是报这个错误。突然想到,上一个查询 out of memory了,难道是这个原因?
新开了窗口,再查询,果然就正常了

望采纳,谢谢