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 = -1, QString name = QString(), QWidget* pWidget = NULL)
        : m_nId(id)
        , m_name(name)
        , m_pWidget(pWidget)
    {}

    ~PersonInfo()
    {
        m_nId = -1;
        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 = 0; i < 10; ++i)
    {
        PersonInfo *pTemp = new PersonInfo(i + 1, 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 ::  10

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。

 

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