qDeleteAll 之后必须清空容器

【1】qDeleteAll应用示例

qDeleteAll源码如下：

 template <typename ForwardIterator>
 Q_OUTOFLINE_TEMPLATE void qDeleteAll(ForwardIterator begin, ForwardIterator end)
 {
     while (begin != end)
     {
         delete *begin;
         ++begin;
     }
 }

 template <typename Container>
 inline void qDeleteAll(const Container &c)
 {
     qDeleteAll(c.begin(), c.end());
 }

示例代码如下：

 #include <QMap>
 #include <QString>
 #include <QWidget>
 #include <QDebug>
 #include <QApplication>

 class PersonInfo
 {
 public:
     PersonInfo(int id = -, QString name = QString(), QWidget* pWidget = NULL)
         : m_nId(id)
         , m_name(name)
         , m_pWidget(pWidget)
     {}

     ~PersonInfo()
     {
         m_nId = -;
         m_name = QString();
         if (m_pWidget != NULL)
         {
             qDebug() << "delete personInfo :: " << this;
             delete m_pWidget;
             m_pWidget = NULL;
         }
     }
 private:
     int m_nId;
     QString m_name;
     QWidget* m_pWidget;
 };

 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);

     QMap<int, PersonInfo *> map;
     for (int i = ; i < ; ++i)
     {
         PersonInfo *pTemp = new PersonInfo(i + , QString("hello World!"), (new QWidget()));
         qDebug() << "construct personInf :: " << pTemp;
         map.insert(i, pTemp);
     }

     qDeleteAll(map); // 1.释放内存
     qDebug() << "after qDeleteAll size :: " << map.size() << endl;
     map.clear(); // 2.必须清空
     qDeleteAll(map); // 3.再次释放内存

     return a.exec();
 }

打印结果如下：

 construct personInf ::  0x3bdc20
 construct personInf ::  0x3c0308
 construct personInf ::  0x3bfe08
 construct personInf ::  0x3c0a88
 construct personInf ::  0x3c1248
 construct personInf ::  0x3c1738
 construct personInf ::  0x3c1bb8
 construct personInf ::  0x3c2420
 construct personInf ::  0x3c26d0
 construct personInf ::  0x3c2c68
 delete personInfo ::  0x3bdc20
 delete personInfo ::  0x3c0308
 delete personInfo ::  0x3bfe08
 delete personInfo ::  0x3c0a88
 delete personInfo ::  0x3c1248
 delete personInfo ::  0x3c1738
 delete personInfo ::  0x3c1bb8
 delete personInfo ::  0x3c2420
 delete personInfo ::  0x3c26d0
 delete personInfo ::  0x3c2c68
 after qDeleteAll size ::  

尤其注意打印结果。

可以尝试把2.清空容器行注释掉，然后再运行程序，查看运行结果。

【2】总结

qDeleteAll只负责释放容器元素内存，但没有对容器的置空操作。若无意间二次再执行qDeleteAll过程，程序必会崩溃。

为了避免可恶的崩溃，切记qDeleteAll之后必须清空容器。

Good Good Study, Day Day Up.

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