c++ - QList方法at()与[]的区别

Question

代码如下：

QList<QVariant> *list;
    for(int i=startrow;i<rowcount+1;i++)
    {
        list=axExcel1.GetSelectSheetOneRowDate(1,i,startcolumn,startcolumn+columncount-1);
        int len=list->length();
        for(int j=0;j<len;j++)
        {
            qDebug()<<list->at(j);
        }
        delete list;list=NULL;
    }

其中

axExcel1.GetSelectSheetOneRowDate(1,i,startcolumn,startcolumn+columncount-1)

返回一个QList<QVariant>*指针,我用list去接收这个指针，然后解析list。
当我使用at()时程序不会崩溃，但当我改为[]访问时如以下代码，程序在进入循环当j=1时在就会崩溃，请问这at()与[]有什么区别？为什么会崩溃？

 qDebug()<<list->[j]；
 

错误提示如下：

Error - RtlWerpReportException failed with status code :-1073741823. Will try to launch the process directly

调试图片

Answer 1

[] has little semantic difference with at, and the implementation is similar
Link from qt official source code

template <typename T>
inline const T &QList<T>::at(int i) const
{ 
    Q_ASSERT_X(i >= 0 && i < p.size(), "QList<T>::at", "index out of range");
     
    return reinterpret_cast<Node *>(p.at(i))->t(); 
}

template <typename T>
inline const T &QList<T>::operator[](int i) const
{ 
    Q_ASSERT_X(i >= 0 && i < p.size(), "QList<T>::operator[]", "index out of range");
    
    return reinterpret_cast<Node *>(p.at(i))->t(); 
}

template <typename T>
inline T &QList<T>::operator[](int i)
{ 
    Q_ASSERT_X(i >= 0 && i < p.size(), "QList<T>::operator[]", "index out of range");
    detach(); // 这里多了一步 !! 
    return reinterpret_cast<Node *>(p.at(i))->t(); 
}

Answer 2

The difference is that at performs an out-of-bounds check, [] does not