C++深浅拷贝——实现String类

来源：互联网发布：做淘宝代销什么好编辑：程序博客网时间：2024/05/30 05:18

浅拷贝：也称位拷贝，编译器只是直接将指针的值拷贝过来，结果多个对象共用同一块内存，当一个对象将这块内存释放掉之后，另一些对象不知道该块空间已经还给了系统，以为还有效，所以在对这段内存进行操作的时候，发生了访问违规。

当类里面有指针对象时，拷贝构造和赋值运算符重载只进行值拷贝(浅拷贝)，两个对象向同一块内存，对象销毁时该空间被释放了两次，因此程序崩溃！

深拷贝：为不同的指针对象各自开辟空间。

浅拷贝实现String类：(错误版)

class String{public:String(const char *str = NULL);String(const String &other);String& operator = (const String &other);~String();private:char *m_data;};String::String(const char *str){if(str == NULL){m_data = new char[1];*m_data = '\0';}else{int length = strlen(str);m_data = new char[length+1];strcpy(m_data, str);}}String::String(const String &other){strcpy(m_data, other.m_data);}String & String::operator =(const String &other){  //检查自赋值if(this == &other){return *this;  }int length = strlen(other.m_data);m_data = new char[length+1];strcpy(m_data, other.m_data);//返回当前对象的引用return *this;}String::~String(){delete[] m_data;m_data = NULL;}int main(){String s;String s1 = "1111";String s4 = "33333";String s5 = "444444";String s6 = "666";String s2(s1);String s3 = "22222";String s7;String s8("hello world!");s1 = s3;system("pause");return 0;}

拷贝构造函数：

赋值运算符的重载：

运行结果：

深拷贝：（普通版）

class String{public:String(const char *str = NULL);String(const String &other);String& operator = (const String &other);~String();private:char *m_data;};String::String(const char *str){if(str == NULL){m_data = new char[1];*m_data = '\0';}else{int length = strlen(str);m_data = new char[length+1];strcpy(m_data, str);}}String::String(const String &other){int length = strlen(other.m_data);m_data = new char[length+1];strcpy(m_data, other.m_data);}String & String::operator =(const String &other){  检查自赋值if(this == &other){return *this;  }释放原有的内存资源delete[] m_data;分配新的内存资源，并复制内容int length = strlen(other.m_data);m_data = new char[length+1];strcpy(m_data, other.m_data);返回当前对象的引用return *this;}String::~String(){delete[] m_data;m_data = NULL;}int main(){String s;String s1 = "1111";String s4 = "33333";String s5 = "444444";String s6 = "666";String s2(s1);String s3 = "22222";String s7;String s8("hello world!");s1 = s3;system("pause");return 0;}

浅拷贝：（引用计数版）

//浅拷贝：引用计数版class String{public:String(char *pStr = ""):_pCount(new int(1)){if(NULL == *pStr){pStr = new char[1];*pStr = '\0';}else{_pStr = new char[strlen(pStr)+1];strcpy(_pStr,pStr);}}String(const String& s):_pStr(s._pStr),_pCount(s._pCount){++(*_pCount);}String& operator = (const String& s){if(--(*_pCount) == 0 && _pStr){delete[] _pStr;delete _pCount;}_pStr = s._pStr;_pCount = s._pCount;++(*_pCount);return *this;}~String(){if(--(*_pCount) == 0){delete[] _pStr;delete _pCount;_pStr = NULL;_pCount = NULL;}}private:char* _pStr;int* _pCount;};

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