qDeleteAll 之后必须清空容器

【1】qDeleteAll应用示例

qDeleteAll源码如下：

 1 template <typename ForwardIterator>
 2 Q_OUTOFLINE_TEMPLATE void qDeleteAll(ForwardIterator begin, ForwardIterator end)
 3 {
 4     while (begin != end)
 5     {
 6         delete *begin;
 7         ++begin;
 8     }
 9 }
10 
11 template <typename Container>
12 inline void qDeleteAll(const Container &c)
13 {
14     qDeleteAll(c.begin(), c.end());
15 }

示例代码如下：

 1 #include <QMap>
 2 #include <QString>
 3 #include <QWidget>
 4 #include <QDebug>
 5 #include <QApplication>
 6 
 7 class PersonInfo
 8 {
 9 public:
10     PersonInfo(int id = -1, QString name = QString(), QWidget* pWidget = NULL)
11         : m_nId(id)
12         , m_name(name)
13         , m_pWidget(pWidget)
14     {}
15 
16     ~PersonInfo()
17     {
18         m_nId = -1;
19         m_name = QString();
20         if (m_pWidget != NULL)
21         {
22             qDebug() << "delete personInfo :: " << this;
23             delete m_pWidget;
24             m_pWidget = NULL;
25         }
26     }
27 private:
28     int m_nId;
29     QString m_name;
30     QWidget* m_pWidget;
31 };
32 
33 int main(int argc, char *argv[])
34 {
35     QApplication a(argc, argv);
36 
37     QMap<int, PersonInfo *> map;
38     for (int i = 0; i < 10; ++i)
39     {
40         PersonInfo *pTemp = new PersonInfo(i + 1, QString("hello World!"), (new QWidget()));
41         qDebug() << "construct personInf :: " << pTemp;
42         map.insert(i, pTemp);
43     }
44 
45     qDeleteAll(map); // 1.释放内存
46     qDebug() << "after qDeleteAll size :: " << map.size() << endl;
47     map.clear(); // 2.必须清空
48     qDeleteAll(map); // 3.再次释放内存
49 
50     return a.exec();
51 }

打印结果如下：

 1 construct personInf ::  0x3bdc20
 2 construct personInf ::  0x3c0308
 3 construct personInf ::  0x3bfe08
 4 construct personInf ::  0x3c0a88
 5 construct personInf ::  0x3c1248
 6 construct personInf ::  0x3c1738
 7 construct personInf ::  0x3c1bb8
 8 construct personInf ::  0x3c2420
 9 construct personInf ::  0x3c26d0
10 construct personInf ::  0x3c2c68
11 delete personInfo ::  0x3bdc20
12 delete personInfo ::  0x3c0308
13 delete personInfo ::  0x3bfe08
14 delete personInfo ::  0x3c0a88
15 delete personInfo ::  0x3c1248
16 delete personInfo ::  0x3c1738
17 delete personInfo ::  0x3c1bb8
18 delete personInfo ::  0x3c2420
19 delete personInfo ::  0x3c26d0
20 delete personInfo ::  0x3c2c68
21 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。

 

Good Good Study, Day Day Up.

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posted @ 2017-09-06 17:17  kaizenly  阅读(3469)  评论(0)  编辑  收藏  举报
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