String类的写时拷贝

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/***********************************************************************************xxx.h:    Copyright , Inc.(2016), All rights reserved.Purpose: 实现String类的写时拷贝模型Author: MaJingCreated Time: 2016-9************************************************************************************/#include <Windows.h>namespace COW1{class String{public:String(const char* str): _str(new char [ strlen(str )+1]){strcpy(_str , str);_refCount = new int(1);}String(const String& s): _refCount(s._refCount), _str(s._str){// 增加引用计数++ _refCount[0];}String& operator =(const String& s){if (this->_str != s._str){// --旧的引用计数，如果是最后一个引用对象，则释放对象_Release();// 成员变量赋值，并增加引用计数_str = s._str;_refCount = s._refCount;++ _refCount[0];}return *this ;}char& operator[](size_t index){// Copy On Writeif (*_refCount > 1){--(*_refCount);char* tmpPtr = new char[strlen(_str) + 1];int* tmpCount = new int(1);strcpy(tmpPtr, _str);_str = tmpPtr;_refCount = tmpCount;}return _str[index];}size_t GetSize (){return strlen (_str);}char* GetStr (){return _str ;}void _Release(){// --旧的引用计数，如果是最后一个引用对象，则释放对象if (--_refCount [0] == 0){delete[] _str ;delete [] _refCount;}}~ String(){_Release();}private:char* _str ;int* _refCount ;     // 引用计数};}namespace COW2{class String{public:String(const char* str):_str(new char[strlen(str) + 5]){// 初始化引用计数_str += 4;GetRefCount(_str) = 1;strcpy(_str, str);}String(const String& s):_str(s._str){// 增加引用计数++GetRefCount(_str);}String& operator=(const String& s){if (this->_str != s._str){Release(_str);_str = s._str;++GetRefCount(_str);}return *this;}char& operator[](size_t index){// Copy On Writeif (GetRefCount(_str) > 1){// 减引用计数--GetRefCount(_str);char* tmpPtr = new char[strlen(_str) + 5];tmpPtr += 4;GetRefCount(tmpPtr) = 1;strcpy(tmpPtr, _str);_str = tmpPtr;}return _str[index];}~String(){Release(_str);}size_t GetSize(){return strlen(_str);}char* GetStr(){return _str;}protected:// 获取引用计数（注意这里返回引用，且注意传入的指针是数据起点）inline int& GetRefCount(char* str){return *(int*)(str-4);}// 引用计数减1，若是最后一个引用对象，则释放对象。inline void Release(char* str){if ((--GetRefCount(str)) == 0){delete[] (str-4);}}private:char* _str;};}// 测试基本的拷贝void TestString_COW1 (){COW1::String s1("hello world!");COW1::String s2 = s1;cout<<"s1:"<<s1.GetStr()<<endl;cout<<"s2:"<<s2.GetStr()<<endl<<endl;s1[0] = 'x';cout<<"s1:"<<s1.GetStr()<<endl;cout<<"s2:"<<s2.GetStr()<<endl<<endl;COW1::String s3("");s3 = s1;cout<<"s3:"<<s3.GetStr()<<endl<<endl;}// 测试COW1效率void TestString_COW2 (){COW1::String s1 = "hello world";int begin = GetTickCount();for (int i = 0; i < 10000; ++i){COW1::String s2 = s1;// do something// cout<<s2.GetStr()<<endl;}int end = GetTickCount();cout<<"cost time:"<<end - begin<<endl;}// 测试什么时候写时拷贝void TestString_COW3(){COW1::String s1("hello world!");COW1::String s2 = s1;COW1::String s3 = s2;cout<<"s1:"<<(int*)s1.GetStr()<<endl;cout<<"s2:"<<(int*)s2.GetStr()<<endl;s2[0] = 'x';cout<<"s1:"<<(int*)s1.GetStr()<<endl;cout<<"s2:"<<(int*)s2.GetStr()<<endl;// 读时也拷贝cout<<s3[0]<<endl;};
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