qt 做的登入框连接数据库时弹出not positioned on a valid record [复制链接]

int login_system(QSqlQuery *query,int id,char *ip,char *pw)//登陆  
{  
query->exec(QString("SELECT COUNT(*) AS cnt FROM usertable WHERE ID=%1 AND PASSWORD='%2'")  
.arg(id).arg(pw));  
query->next();  
if(query->value(0).toInt()==0)  
return 1;  
query->exec(QString("select ONLINE from usertable where ID=%1").arg(id));  
query->next();  
if(query->value(0).toInt()==1)  
return 2;  
if(query->exec(QString("select IP from iptable where IP='%1'").arg(ip)))  
{  
if(query->next())  
return 3;  
else if(query->exec(QString("SELECT NAME,PIC FROM usertable where ID=%1").arg(id)))  
{  
query->exec(QString("INSERT INTO iptable VALUE('%1',%2)").arg(ip).arg(id));  
query->exec(QString("update usertable set ONLINE=1 where ID=%1").arg(id));  
query->exec(QString("SELECT NAME,PIC FROM usertable where ID=%1").arg(id));  
return 0;  
}  
else  
{  
return 4;  
}  
}  
else  
return 5;  
}  

以上是源码，输入id和密码后，弹出QSqlQuery::value: not positioned on a valid record的错误？？  

query->next();  改成 while(query->next()) {}  

谢谢。可以了。。。