C++字符串重载运算符函数（剑指offer面试题1）

//剑指offer面试题1：重载运算符函数
//题目：如下为类型CMyString的声明，请为该类型添加多种运算符函数。
#include<iostream>
#include<cstring>
#include<cstdio>

using namespace std;

class CMyString
{
    friend ostream& operator<<(ostream &out, const CMyString &str);//输出流重载函数
    friend istream& operator>>(istream &in, CMyString &str);//输入流重载函数
public:
    CMyString(char* pData = nullptr);   //有参构造函数
    CMyString(const CMyString& str);    //拷贝构造函数
    ~CMyString(void);                   //析构函数

    CMyString& operator = (const CMyString &str);//重载赋值运算符函数
    CMyString& operator += (const CMyString &str);//重载+=运算符函数
    CMyString& operator + (const CMyString &str);//重载+运算符函数

    void show();
private:
    char* m_pData;
};

ostream &operator<<(ostream &out, const CMyString &str)
{
    out << str.m_pData << endl;
    return out;
}

istream &operator>>(istream &in, CMyString &str)
{
    in >> str.m_pData;
    return in;
}

CMyString::CMyString(char *pData)
{
    if (pData == nullptr)
    {
        m_pData = new char[1];
        m_pData[0] = '\0';      //'\0'表示空字符，作为字符串结束符使用
    }
    else
    {
        m_pData = new char[strlen(pData) + 1];
        strcpy(m_pData, pData);
    }
}

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

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

CMyString& CMyString::operator = (const CMyString &str)
{
    //判断传入的参数和当前的实例（*this）是不是同一个实例
    if (this == &str)
        return *this;

    //分配新内存之前释放自身已有的内存，防止程序出现内存泄漏
    delete[]m_pData;
    m_pData = nullptr;

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

    return *this;
}

CMyString& CMyString::operator += (const CMyString &str)
{
    char *str1; //临时的字符串存放指针
    if (str.m_pData == nullptr)
        return *this;
    else
    {
        str1 = new char[strlen(m_pData) + strlen(str.m_pData) + 1];
        strcpy(str1, m_pData);
        strcat(str1, str.m_pData);
    }
    delete[]m_pData;
    m_pData = str1;
    return *this;

}
CMyString& CMyString::operator + (const CMyString &str)
{
    char *temp;//临时的字符串存放指针
    if (str.m_pData == nullptr)
        return *this;
    else
    {
        temp = new char[strlen(m_pData) + strlen(str.m_pData) + 1];
        strcpy(temp, m_pData);
        strcat(temp, str.m_pData);
    }
    delete[]m_pData;
    m_pData = temp;
    return *this;

}
//===============测试代码========================//
void CMyString::show()
{
    cout << m_pData << endl;
}


//赋值重载函数测试
void Test1()
{
    cout << "******************Test1(赋值)*****************" << endl;
    char *text = "Hello world";

    CMyString str1(text);
    CMyString str2;
    str2 = str1;
    cout << "The expected result is:" << text << endl;

    cout << "The actual result is:";
    str2.show();
    cout << endl;
}

//加法重载函数测试
void Test2()
{
    cout << "*********************Test2(加法)******************" << endl;
    char *text1 = "shuang";
    char *text2 = "is a beautiful girl!";

    CMyString str1(text1);
    CMyString str2(text2);
    CMyString str;
    cout << "The expected result is:" << text1 << " " << text2 << endl;
    str1 += str2;
    cout << "str1 += str2:";
    str1.show();

    CMyString str3 = "hai";
    CMyString str4 = "Merry";
    str = str3 + str4;
    cout << "str3 + str4:" << str << endl;
    //str3.show();

}

//输入输出流测试
void Test3()
{
    CMyString str1;
    CMyString str2;
    cin >> str1 >> str2;
    cout << "str1:" << str1 << endl;
    cout << "str2:" << str2 << endl;
}


int main(int argc, char *argv[])
{
    Test1();
    Test2();
    Test3();
    return 0;
}