面试题1：赋值运算符函数

要点：

1. 判断传入参数和this是否是同一个

2. operator的参数设为常量引用，否则从形参到实参会调用赋值构造函数

3. 释放自己已有内存

4. 返回值为引用，才可以允许连续赋值

赋值运算符重载返回本类引用，形参是const引用

5. 要用strcpy，vs13用strcpy_s(m_pData, strlen(str.m_pData) + 1, str.m_Pdata)

class CMyString
{
public:
CMyString(char* pData = NULL);
CMyString(const CMyString& str);
~CMyString(void);

CMyString& operator = (const CMyString& str);

void Print();

private:
char* m_pData;
};

CMyString& CMyString::operator = (const CMyString& str)
{
if(this == &str)
return *this;

delete []m_pData;
m_pData = NULL;

m_pData = new char[strlen(str.m_pData) + 1];
strcpy(m_pData, str.m_pData);

return *this;
}

完整代码：

// AssignmentOperator.cpp : Defines the entry point for the console application.
//

// 《剑指Offer——名企面试官精讲典型编程题》代码
// 著作权所有者：何海涛

#include "stdafx.h"
#include <string>

class CMyString
{
public:
CMyString(char* pData = NULL);
CMyString(const CMyString& str);
~CMyString(void);

CMyString& operator = (const CMyString& str);

void Print();

private:
char* m_pData;
};

CMyString::CMyString(char *pData)
{
if(pData == NULL)
{
m_pData = new char[1];
m_pData[0] = '\0';
}
else
{
int length = strlen(pData);
m_pData = new char[length + 1];
strcpy(m_pData, pData);
}
}

CMyString::CMyString(const CMyString &str)
{
int length = strlen(str.m_pData);
m_pData = new char[length + 1];
strcpy(m_pData, str.m_pData);
}

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

CMyString& CMyString::operator = (const CMyString& str)
{
if(this == &str)
return *this;

delete []m_pData;
m_pData = NULL;

m_pData = new char[strlen(str.m_pData) + 1];
strcpy(m_pData, str.m_pData);

return *this;
}

// ====================测试代码====================
void CMyString::Print()
{
printf("%s", m_pData);
}

void Test1()
{
printf("Test1 begins:\n");

char* text = "Hello world";

CMyString str1(text);
CMyString str2;
str2 = str1;

printf("The expected result is: %s.\n", text);

printf("The actual result is: ");
str2.Print();
printf(".\n");
}

// 赋值给自己
void Test2()
{
printf("Test2 begins:\n");

char* text = "Hello world";

CMyString str1(text);
str1 = str1;

printf("The expected result is: %s.\n", text);

printf("The actual result is: ");
str1.Print();
printf(".\n");
}

// 连续赋值
void Test3()
{
printf("Test3 begins:\n");

char* text = "Hello world";

CMyString str1(text);
CMyString str2, str3;
str3 = str2 = str1;

printf("The expected result is: %s.\n", text);

printf("The actual result is: ");
str2.Print();
printf(".\n");

printf("The expected result is: %s.\n", text);

printf("The actual result is: ");
str3.Print();
printf(".\n");
}

int _tmain(int argc, _TCHAR* argv[])
{
Test1();
Test2();
Test3();
system("pause");

return 0;
}

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