//1 内存泄漏 str1所指的资源没有被释放
{string* str1 = new string("hello");string* str2 = new string("world");
}//2 多重释放，引起程序崩溃
{string* str1 = new string("hello");delete str1;//...delete str1;//引起程序崩溃
}

#pragma oncetemplate<class T>
class SharedPointer
{public://默认构造函数，内部指针，未指向任何资源，引用计数为0,因为它未与任何资源绑定SharedPointer() :m_refCount(nullptr), m_pointer(nullptr){}//构造函数，初始化时，指向一个已经分配好的资源SharedPointer(T* adoptTarget) :m_refCount(nullptr), m_pointer(adoptTarget){addReference();}//构造函数，使用其它对象创建新对象SharedPointer(const SharedPointer<T>& copy):m_refCount(copy.m_refCount), m_pointer(copy.m_pointer){addReference();}//析构函数，引用计数递减，当为0时，释放资源virtual ~SharedPointer(){removeReference();}//赋值操作//当左值被赋值时，表明它不再指向所指的资源，故引用计数减一//之后，它指向了新的资源，所以对应这个资源的引用计数加一SharedPointer<T>& operator=(const SharedPointer<T>& that){if (this != &that){removeReference();this->m_pointer = that.m_pointer;this->m_refCount = that.m_refCount;addReference();}return *this;}//判断是否指向同一个资源bool operator==(const SharedPointer<T>& other){return m_pointer == other.m_pointer;}bool operator!=(const SharedPointer<T>& other){return !operator==(other);}//指针解引用T& operator*() const{return *m_pointer;}//调用所知对象的公共成员T* operator->() const{return m_pointer;}//获取引用计数个数int GetReferenceCount() const{if (m_refCount){return *m_refCount;} else{return -1;}}protected://当为nullpter时，创建引用计数资源，并初始化为1//否则，引用计数加1。void addReference(){if (m_refCount){(*m_refCount)++;}else{m_refCount = new int(0);*m_refCount = 1;}}//引用计数减一，当变为0时，释放所有资源void removeReference(){if (m_refCount){(*m_refCount)--;if (*m_refCount == 0){delete m_refCount;delete m_pointer;m_refCount = 0;m_pointer = 0;}}}private:int * m_refCount;T   * m_pointer;
};

#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include "SharedPointer.h"using namespace std;
class MyClass
{public:~MyClass(){cout << "释放MyClass(" << _id << ")n";}MyClass(int i) :_id(i){}void Print() const{cout << "MyClass(" << _id << ")" << endl;}
private:int _id;
};int main()
{{MyClass* px = new MyClass(1);SharedPointer<MyClass> ap(px);SharedPointer<MyClass> bp = ap;SharedPointer<MyClass> cp;cout << "ap的引用计数(2): "<< ap.GetReferenceCount() << endl;cout << "将ap赋值给cpn";cp = ap;cout << "ap的引用计数(3): "<< ap.GetReferenceCount() << endl;MyClass* qx = new MyClass(5);SharedPointer<MyClass> dp(qx);ap = dp;cout << "ap的引用计数(2): "<< ap.GetReferenceCount() << endl;cout << "dp的引用计数(2): "<< dp.GetReferenceCount() << endl;//"像指针一样使用智能指针"dp->Print();(*cp).Print();}cin.get();
}