void Widget::on_pushButton_5_clicked()                           
{                                                                
                                                                 
    ui->listWidget->clear(); //先清空显示                             
    QFile file("my.xml");                                        
    if (!file.open(QIODevice::ReadOnly)) return ;                
    QDomDocument doc;                                            
    if (!doc.setContent(&file))                                  
    {                                                            
    file.close();                                                
    return ;                                                     
    }                                                            
    file.close()                                                 
    //返回根节点及其子节点的元素标记名                                           
    QDomElement docElem = doc.documentElement();  //返回根元素        
    QDomNode n = docElem.firstChild();   //返回根节点的第一个子节点          
    while(!n.isNull())  //如果节点不为空                                
    {                                                            
    if (n.isElement()) //如果节点是元素                                 
    {                                                            
    QDomElement e = n.toElement(); //将其转换为元素                     
    ui->listWidget->addItem(e.tagName()+e.attribute(tr("编号")));  
    QDomNodeList list = e.childNodes();                          
    for(int i=0; i<list.count(); i++)                            
    {                                                            
    QDomNode node = list.at(i);                                  
    if(node.isElement())                                         
    ui->listWidget->addItem("   "+node.toElement().tagName()     
    +" : "+node.toElement().text());                             
    }                                                            
    }                                                            
    n = n.nextSibling();  //下一个兄弟节点                              
    }                                                            
}                                                                
运行结果出现
In menber function'void Widget::on_pushButton_5_clicked()':  
expected':'before'QDomElement'
'docElem' was not declared in this scope