剑指offer-0x01

赋值运算函数

对于定义一个赋值运算符函数时，需要注意一下几点：

函数的返回类型必须是一个引用，因为只有返回引用，才可以连续赋值

传入的参数声明为常量引用，可以提高代码效率，同时赋值运算函数内不会改变传入的实例状态

一定要记得释放实例自身已有的内存，否则程序容易出现内存泄露

注意传入的参数和当前的实例是不是同一个实例，如果是同一个，则不用进行赋值操作，直接返回即可

自己的代码 求鄙视

//main.h
#ifndef MAIN_H_INCLUDED
#define MAIN_H_INCLUDED

class CMyString
{

public:
    CMyString(char* pData = NULL);
    CMyString(const CMyString & str);
    char* getStr();
    ~CMyString();

    CMyString& operator = (const CMyString &str);
private:
    char* m_pdata;


};


#endif // MAIN_H_INCLUDED

//main.cpp
#include <iostream>
#include <cstring>
#include "main.h"//must use "" not <>
using namespace std;

CMyString& CMyString::operator = (const CMyString &str)
{
    if (this == &str)
        return *this;//if itself = itself then return directly
        //in case delete itself when delete
        delete []m_pdata;
        m_pdata = NULL;
        m_pdata = new char[strlen(str.m_pdata)+1];
        strcpy(m_pdata,str.m_pdata);
        return *this;//return a value
}
char* CMyString::getStr()
{
    return m_pdata;
}
CMyString::CMyString(char* pData)
{
    int length = strlen(pData);
        m_pdata = new char[length+1];
        strcpy(m_pdata,pData);
}

CMyString::~CMyString()
{
    delete []m_pdata;
}
int main()
{
    CMyString str("i love china!");
    CMyString str1;
    str1 = str;
    cout<<str1.getStr()<<endl;
    cout << "Hello world!" << endl;
    return 0;
}

E:\CodeBlocks\operator\main.h|14|error: 'char* CMyString::m_pdata' is private|

别人的代码

#include<iostream>
#include<cstring>
using namespace std;

class CMyString
{
public:
    CMyString(char *pData=NULL);
    CMyString(CMyString &str);
    CMyString& operator=(CMyString &str);
    ~CMyString(void);
    void Print(){ cout << m_pData; }
private:
    char* m_pData;

};

CMyString::CMyString(char *pData)
{
    if (NULL == pData)
    {
        m_pData = NULL;
        return;
    }
    else
    {
        unsigned int len = strlen(pData)+1;
        m_pData = new char[len];
        for (int i = 0; i < len; i++)
            m_pData[i] = pData[i];
        m_pData[len] = '\0';
    }
}

CMyString::CMyString(CMyString &str)
{
    unsigned int len = strlen(str.m_pData) + 1;
    m_pData = new char[len];
    for (int i = 0; i < len; i++)
        m_pData[i] = str.m_pData[i];
    m_pData[len] = '\0';
}

CMyString & CMyString::operator=(CMyString &str)
{
    if (this == &str)
        return *this;
    else
    {
        unsigned int len = strlen(str.m_pData) + 1;
        char *pTemp = new char[len];
        for (int i = 0; i < len; i++)
            pTemp[i] = str.m_pData[i];
        pTemp[len] = '\0';

        delete[]m_pData;//出错！！！不解

        m_pData = pTemp;

    }
    return *this;
}

CMyString::~CMyString()
{
    delete [] m_pData;
}

int main()
{
    char c1[10] = "majunfu";
    CMyString s1(c1);
    CMyString s2 = s1;
    s1 = s2;
    s1.Print();
    s2.Print();
    return 0;
}