#include<cstring>
#include<cstdio>class CMyString
{
public:CMyString(char * pData = nullptr);CMyString(const CMyString& str);~CMyString(void);CMyString& operator=(const CMyString& str);void Print();private:char* m_pData;  //类比C风格字符串
};CMyString::CMyString(char * pData)
{if (pData==nullptr)  //空指针
    {//创建空字符串m_pData = new char[1];m_pData[0] = '\0';}else{int length = strlen(pData);m_pData = new char[length + 1];//复制/*char * strcpy(char * destination, const char * source);Copies the C string pointed by source into the array pointed by destination, including the terminating null character(and stopping at that point).*/strcpy(m_pData, pData);}
}CMyString::CMyString(const CMyString& str)
{int length = strlen(str.m_pData);  //Returns the length of the C string str. The length of a C string is determined by the terminating null - characterm_pData = new char[length + 1];  //new分配内存后，默认使用delete释放对象
    strcpy(m_pData, str.m_pData);
}CMyString::~CMyString(void)
{delete[] m_pData;
}//1. 返回值的类型声明为该类型的引用，程序结束前返回实例自身的引用（*this）
//2. 传入的参数的类型声明为常量引用
//3. 释放实例自身的内存
//4. 判断传入的参数和当前的实例是不是同一个实例
//5. 升级：考虑异常安全性的解法 先new再delete
CMyString& CMyString::operator=(const CMyString& str)  //参考2
{if (this != &str)  //参考4
    {CMyString strTemp(str);  //临时实例//参考3char* pTemp = strTemp.m_pData;strTemp.m_pData= m_pData;m_pData = pTemp;}//调用strTemp的析构函数，释放其内存//参考1return *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 main(int argc, char* argv[])
{Test1();Test2();Test3();getchar();  //等待输入return 0;
}