當指針超出范圍后就會刪除被引用的對象。 與QPointer不同，他可以在任意類型中使用（QPointer只能在identity type中使用） 4個不同的清除類 ? ? ? ? 1. QScopedPointerDeleter ? 2. QScopedPointerArrayDeleter ? 3. QScopedPointerArrayDeleter ? 4. QScopedPointerDeleteLater 如下例子：QScopedPointer<int, QScopedPointerArrayDeleter<int>> intArrayPointer(new int(100)); 在如下幾個方面用得比較多： 異常 使代碼簡潔 通常用于刪除動態分配的變量。

QPointerQScopedPointer基本上用用動態分配的對象，在范圍外自動進行釋放，這個范圍是通過{}包起來的，也就是函數的生存周期。

如下面這個原始代碼：

void myFunction(bool useSubClass){MyClass *p = useSubClass ? new MyClass() : new MySubClass;QIODevice *device = handsOverOwnership();if (m_value > 3) {delete p;delete device;return;}try {process(device);}catch (...) {delete p;delete device;throw;}delete p;delete device;}

使用了QScopedPointer后：

void myFunction(bool useSubClass){// assuming that MyClass has a virtual destructorQScopedPointer<MyClass> p(useSubClass ? new MyClass() : new MySubClass);QScopedPointer<QIODevice> device(handsOverOwnership());if (m_value > 3)return;process(device);}

帶限定符的C++指針使用QScopedPointer：

const QWidget *const p = new QWidget();// is equivalent to:const QScopedPointer<const QWidget> p(new QWidget());QWidget *const p = new QWidget();// is equivalent to:const QScopedPointer<QWidget> p(new QWidget());const QWidget *p = new QWidget();// is equivalent to:QScopedPointer<const QWidget> p(new QWidget());

自定義清空

相當于delete操作QScopedPointerDeleter

相當于delete?[]操作QScopedPointerArrayDeleter

相當于free操作QScopedPointerPodDeleter

相當于deleteLater操作QScopedPointerDeleteLater

代碼如下：

// this QScopedPointer deletes its data using the delete[] operator:QScopedPointer<int, QScopedPointerArrayDeleter<int> > arrayPointer(new int[42]);// this QScopedPointer frees its data using free():QScopedPointer<int, QScopedPointerPodDeleter> podPointer(reinterpret_cast<int *>(malloc(42)));// this struct calls "myCustomDeallocator" to delete the pointerstruct ScopedPointerCustomDeleter{static inline void cleanup(MyCustomClass *pointer){myCustomDeallocator(pointer);}};// QScopedPointer using a custom deleter:QScopedPointer<MyCustomClass, ScopedPointerCustomDeleter> customPointer(new MyCustomClass);

下面是在類聲明的時候要注意的問題：

class MyPrivateClass; // forward declare MyPrivateClassclass MyClass{private:QScopedPointer<MyPrivateClass> privatePtr; // QScopedPointer to forward declared classpublic:MyClass(); // OKinline ~MyClass() {} // VIOLATION - Destructor must not be inlineprivate:Q_DISABLE_COPY(MyClass) // OK - copy constructor and assignment operators// are now disabled, so the compiler won't implicitely// generate them.};

運行截圖如下：

代碼如下：

#ifndef CLASSA_H #define CLASSA_H#include <QString> #include <QDebug>class ClassA;struct ClassACustomDeleter{static inline void cleanup(ClassA *p){qDebug() << "static inline void cleanup(ClassA *p) called";delete p;} };class ClassA { public:ClassA();~ClassA();const QString &getStr();const int &getValue();private:QString m_str;int m_value; };#endif // CLASSA_H

ClassA.cpp

#include "ClassA.h" #include <QDebug>ClassA::ClassA() : m_str("字符串"), m_value(10) {}ClassA::~ClassA() {qDebug() << "ClassA::~ClassA() called"; }const QString &ClassA::getStr() {return m_str; }const int &ClassA::getValue() {return m_value; }

main.cpp

#include <QCoreApplication> #include <QDebug> #include <QScopedPointer> #include "ClassA.h"void normalFunction(){ClassA *a = new ClassA;try {if(0 == 0){throw "error";}}catch(char const *err) {qDebug() << err;delete a;return;}//want to do sth//...//welldelete a; }void usingQScopedFunction(){QScopedPointer<ClassA> p(new ClassA); }void usingQScopedCustomFunction(){QScopedPointer<ClassA, ClassACustomDeleter> p(new ClassA); }int main(int argc, char *argv[]) {QCoreApplication a(argc, argv);normalFunction();qDebug() << "------------華麗的分割線------------";usingQScopedFunction();qDebug() << "------------華麗的分割線------------";usingQScopedCustomFunction();return a.exec(); }

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