2022.12.7---运算符重载

封装my_string并实现=、+、==、！=、==、>、<、<<、>>等运算符的重载

#include <iostream>
#include<cstring>

using namespace std;

class my_string
{
private:
    char *cstr;
    int len;
public:
    my_string():cstr(NULL),len(0) {/*cout<<"无参构造"<<endl;*/}  //无参构造函数
    my_string(const char *str)    //有参构造函数
    {
        len=strlen(str);
        cstr=new char[len+1];
        strcpy(cstr,str);
        //cout<<"有参构造"<<endl;
    }
    my_string(const my_string &other)    //拷贝构造函数
    {
        this->len=other.len;
        this->cstr=new char[len+1];
        strcpy(this->cstr,other.cstr);
        //cout<<"拷贝构造"<<endl;
    }
    ~my_string()    //析构函数
    {
        if(cstr!=NULL)
        {
            delete cstr;
        }
        cout<<"析构函数"<<endl;
    }

    //运算符重载
    friend istream &operator>>(istream &L,my_string &R);// >>重载
    friend ostream &operator<<(ostream &L,my_string &R);// <<重载
    my_string &operator=(my_string &R)      //运算符重载=
    {
        if(this->cstr!=NULL)
        {
            strcpy(this->cstr,R.cstr);
            this->len=R.len;
        }
        else
        {
            this->cstr=new char[R.len+1];
            strcpy(this->cstr,R.cstr);
            this->len=R.len;
        }
        return *this;
    }
    my_string &operator+(const my_string &R)   //运算符重载+，字符串加字符串
    {
        strcat(this->cstr,R.cstr);
        this->len+=R.len;
        return *this;
    }
    my_string &operator+(const char ch)   //运算符重载+，字符串加字符
    {
        this->len+=1;
        this->cstr[this->len-1]=ch;
        return *this;
    }
    bool operator==(const my_string &R)const    //运算符重载==
    {
        return ~strcmp(this->cstr,R.cstr);
    }
    bool operator!=(const my_string &R)const    //运算符重载!=
    {
        return strcmp(this->cstr,R.cstr);
    }
    bool operator>(const my_string &R)const    //运算符重载>
    {
        return ~strcmp(this->cstr,R.cstr);
    }
    bool operator<(const my_string &R)const    //运算符重载<
    {
        return strcmp(this->cstr,R.cstr);
    }
};

istream &operator>>(istream &L,my_string &R)
{
    if(R.cstr!=NULL)
    {
        L>>R.cstr;
        R.len=strlen(R.cstr);
    }
    else
    {
        R.cstr=new char[20];
        L>>R.cstr;
        R.len=strlen(R.cstr);
    }
    return L;
}
ostream &operator<<(ostream &L,my_string &R)
{
    L<<R.cstr;
    return L;
}

int main()
{
    my_string s;                    //s调用无参构造
    cout<<"请输入一个字符串:";
    cin>>s;                         // >>运算符重载
    cout<<"s: "<<s<<endl;            // <<运算符重载
    my_string s1("helloya");        //s1调用有参构造
    cout<<"s1: "<<s1<<endl;          // <<运算符重载
    my_string s2;                   //s2调用无参构造
    s2=s;                           // =运算符重载
    cout<<"s2=s: "<<s2<<endl;
    if(s1!=s2)                      // !=运算符重载
    {
        cout<<"s1和s2不相等"<<endl;
        if((s1>s2)>0)                   // >运算符重载
        {
            cout<<"s1大于s2"<<endl;
        }else
        {
            cout<<"s1小于s2"<<endl;
        }
    }else
    {
        cout<<"s1和s2相等"<<endl;
    }
    cout<<"s2+'h': "<<s2+'h'<<endl; // +运算符重载
    cout<<"s1+s2: "<<s1+s2<<endl;    // +运算符重载

    return 0;
}