C++ 移动赋值运算符

1移动赋值运算符.cpp

#include<iostream>
#include<string.h>
using namespace std;

class my_string{
    char* p=nullptr;
    public:
    my_string(){}
    my_string(const char* s){
        if(s){
            p = new char[strlen(s)+1];
            strcpy(p,s);
        }
    }
    my_string( const my_string& ms){
        cout<<"copy construction"<<endl;
        if(ms.p){
            if(p)delete []p;
            p = new char[ms.size()+1];
            strcpy(p,ms.p);
        }
    }
    ~my_string(){
        if(p)delete [] p;
    }
    my_string(my_string && s)
    {
        cout<<"move construction"<<endl;
        p = s.p;
        s.p =nullptr;
    }
friend ostream &operator<<(ostream&cout,my_string s);
    char & operator[](int pos)
    {
        return p[pos];
    }
    int size()const{return strlen(p);}
    my_string operator+(my_string &s)
    {
        my_string tmp;
        tmp.p= new char[this->size()+s.size()+1];
        strcpy(tmp.p,this->p);
        strcat(tmp.p,s.p);
        return tmp;
    }
    my_string operator+(const char* s)
    {
        my_string tmp;
        tmp.p= new char[this->size()+strlen(s)+1];
        strcpy(tmp.p,this->p);
        strcat(tmp.p,s);
        return tmp;
    }
    my_string &operator=(my_string &&s)
    {
        cout<<"move assignment=(&&)"<<endl;
        p = s.p;
        s.p =nullptr;

    }
};

ostream &operator<<(ostream&cout,my_string s)
{
    cout<<s.p;
    return cout;
}

int main()
{
    my_string s1="123";
    my_string s2="456";
    my_string s3;
    //不要把一个左值轻易转换为右值使用，除非你确定它在下面不再被使用
//err:  my_string s4(std::move(s1));

    //移动赋值运算，提高了运算效率，没有拷贝的过程
    s3 =s1+s2;
    //(a=b)=c;
    int a=1,b=1,c=1;
    (a=b)=c;
    return 0;
}