mystring类的实现

mystring.h文件

#ifndef _CMYSTRING_H_#define _CMYSTRING_H_#include <iostream>#include <cstring>class CMyString{public: //default ctor    CMyString(const char *s = nullptr)    {        if (!s)        {            _data = new char[1];            *_data = '\0';            return;        }        _data = new char[strlen(s) + 1];        strcpy(_data, s);    }    //copy ctor    CMyString(const CMyString &other)    {        _data = new char[strlen(other._data) + 1];        strcpy(_data, other._data);    }    //dtor    ~CMyString()     {        delete [] _data;    }    //assign operator     CMyString& operator=(const CMyString &other)    {        if(this == &other)            return *this;        delete _data;        _data = new char[strlen(other._data) + 1];        strcpy(_data, other._data);        return *this;    }    friend std::ostream& operator<<(std::ostream &os, const CMyString &s)    {        os << s._data;        return os;    } private:    char *_data;};#endif

main.cpp文件

#include <iostream>#include "mystring.h"using namespace std;int main(int argc, char *argv[]){    CMyString str1;    CMyString str2("hello,world");    CMyString str3(str2);    CMyString str4("hi,world");    str1 = str3 = str4;    cout << str1 << " " << str2 << " " << str3 << " " << str4 << endl;    return 0;}

异常安全性

考虑赋值运算符中new会产生异常，为了写出异常安全性的代码，上面的代码有两种修改方案：
1. 先new，成功之后再delete掉，不成功则返回原来的状态
2. 先产生一个暂时的栈实例，然后交换两者的数据成员（字符指针）,当跳出作用域后，栈实例销毁会销毁原来的数据成员

方案1

CMyString& operator= (const CMyString& other){    if(this == &other)        return *this;    char *old_data = _data;    _data = new char[strlen(other._data) + 1];    if (!_data)        return *this;    delete old_data;    strcpy(_data, other._data);    return *this;}

方案2

CMyString& operator=(const CMyString &other){    CMyString tmp_str(other);    char *tmp_data = tmp_str._data;    tmp_str._data = _data;    _data = tmp_data;    return *this;}