C++使用mysql判断select查询结果是否为空mysql_query返回值问题

MYSQL sqlcon;
string str = "SELECT * FROM dt_user where user =.........."	
if (!mysql_query(&(this->sqlcon), str)
	{
		return true;
	}

MYSQL sqlcon;
MYSQL_RES * result;
mysql_query(&(this->sqlcon), str);
		result = mysql_store_result(&(this->sqlcon));
		while ((row = mysql_fetch_row(result)))  
            //当mysql_fetch_row返回NULL时，row = NULL 这个表达式的bool为假
		{
			return true;
		}