【C++】 61_智能指针类模板

智能指针智能指针的意义现代 C++ 开发库中最重要的类模板之一C++ 中内存管理的主要手段能够在很大程度上避开内存相关的问题内存泄漏内存多次释放STL 中的智能指针 auto_ptr生命周期结束时，销毁指向的内存（防止内存泄漏）不能指向堆数组，只能指向堆对象（变量）一片堆空间只属于一个智能指针对象（防止内存多次释放）多个智能指针对象不能指向同一片堆空间编程实验： auto_ptr 使用初探#include <iostream>#include <memory>using namespace std;class Test{private: string m_name; public: Test(const char* name) { cout << “Hello, " << name << endl; m_name = name; } void print() { cout << “I’m " << m_name << endl; } ~Test() { cout << “Goodbye, " << m_name << endl; }};int main(){ auto_ptr<Test> pt(new Test(“D.T.Software”)); cout << “pt = " << pt.get() << endl; pt->print(); cout << endl; auto_ptr<Test> pt1(pt); // 所有权转移： pt ==> pt1 cout << “pt = " << pt.get() << endl; cout << “pt = " << pt1.get() << endl; pt1->print(); return 0;}输出：Hello, D.T.Softwarept = 0x90e7008I’m D.T.Softwarept = 0pt = 0x90e7008I’m D.T.SoftwareGoodbye, D.T.SoftwareSTL 中的其它指针share_ptr带有引用计数机制，支持多个指针对象指向同一片内存空间weak_ptr配合 shared_ptr 而引入的一种智能指针unique_ptr一个指针对象指向一片内存空间，不能拷贝构造和赋值Qt 中的智能指针QPointer当其指向的对象被销毁时，他会被自动置空(防止内存多次释放)析构时不会自动销毁所指向的对象QSharedPointer引用计数型智能指针可以被自由的拷贝和赋值当引用计数为 0 时才删除指向的对象（防止内存泄漏）编程实验： Qt中的智能指针#include <QtCore/QCoreApplication>#include <QDebug>#include <QPointer>#include <QSharedPointer>class Test : public QObject{private: QString m_name;public: Test(const char* name) { qDebug() << “Hello, " << name; m_name = name; } void print() { qDebug() << “I’m " << m_name; } ~Test() { qDebug() << “Goodbye, " << m_name; }};int main(){ QPointer<Test> pt(new Test(“D.T.Software”)); QPointer<Test> pt1(pt); QPointer<Test> pt2(pt); pt->print(); pt1->print(); pt2->print(); delete pt; qDebug() << “pt = " << pt; qDebug() << “pt1 = " << pt; qDebug() << “pt2 = " << pt; qDebug(); QSharedPointer<Test> spt(new Test(“D.T.Software”)); QSharedPointer<Test> spt1(spt); QSharedPointer<Test> spt2(spt); spt->print(); spt1->print(); spt2->print(); return 0;}输出：Hello, D.T.SoftwareI’m “D.T.Software"I’m “D.T.Software"I’m “D.T.Software"Goodbye, “D.T.Software"pt = QObject(0x0)pt1 = QObject(0x0)pt2 = QObject(0x0)Hello, D.T.SoftwareI’m “D.T.Software"I’m “D.T.Software"I’m “D.T.Software"Goodbye, “D.T.Software"Qt 中的其它智能指针QWeakPointerQScopedPointerQScopedArrayPointerQSharedDataPointerQExplicitlySharedDataPointer编程实验：创建智能指针类模板SmartPointer.h#ifndef SMARTPOINTER_H#define _SMARTPOINTER_H_template< typename T >class SmartPoniter{private: T* m_pointer;public: SmartPoniter(T* p = NULL); SmartPoniter(const SmartPoniter<T>& obj); SmartPoniter<T>& operator = (const SmartPoniter<T>& obj); T* operator -> (); T& operator * (); bool isNull(); T* get(); ~SmartPoniter();};template< typename T >SmartPoniter<T>::SmartPoniter(T* p){ m_pointer = p;}template< typename T >SmartPoniter<T>::SmartPoniter(const SmartPoniter<T>& obj){ m_pointer = obj.m_pointer; // 所有权转接 const_cast<SmartPoniter<T>&>(obj).m_pointer = NULL;}template< typename T >SmartPoniter<T>& SmartPoniter<T>::operator = (const SmartPoniter<T>& obj){ if( this != &obj ) { delete m_pointer; // 所有权转接 m_pointer = obj.m_pointer; const_cast<SmartPoniter<T>&>(obj).m_pointer = NULL; } return this;}template< typename T >T SmartPoniter<T>::operator -> (){ return m_pointer;}template< typename T >T& SmartPoniter<T>::operator * (){ return m_pointer;}template< typename T >bool SmartPoniter<T>::isNull(){ return (m_pointer == NULL);}template< typename T >T SmartPoniter<T>::get(){ return m_pointer;}template< typename T >SmartPoniter<T>::~SmartPoniter(){ delete m_pointer; }#endifmain.cpp#include <iostream>#include <memory>#include “SmartPointer.h"using namespace std;class Test{private: string m_name; public: Test(const char* name) { cout << “Hello, " << name << endl; m_name = name; } void print() { cout << “I’m " << m_name << endl; } ~Test() { cout << “Goofbye, " << m_name << endl; }};int main(){ SmartPoniter<Test> pt(new Test(“D.T.Software”)); cout << “pt = " << pt.get() << endl; pt->print(); cout << endl; SmartPoniter<Test> pt1(pt); cout << “pt = " << pt.get() << endl; cout << “pt = " << pt1.get() << endl; pt1->print(); return 0;}输出：Hello, D.T.Softwarept = 0x815e008I’m D.T.Softwarept = 0pt = 0x815e008I’m D.T.SoftwareGoofbye, D.T.Software小结智能指针是 C++ 中自动内存管理的主要手段智能指针在各种平台上都有不同的表现形式智能指针能够尽可能的避开内存相关的问题STL 和 Qt 中都提供了对智能指针的支持以上内容参考狄泰软件学院系列课程，请大家保护原创