89.赋值重载以及深浅拷贝

• 非指针,则深浅拷贝都一样,含有指针则内存共享,指针一致,内容一直
• 深拷贝,指针不一致,内存一直,内存是独享的
• 赋值重载如果有返回自身类型对象,会调用拷贝构造,需要重载拷贝构造,这一点是必须要注意的,原理是:先操作一个类,再把操作的这个类拷贝到本类中,即使返回(*this),也会调用 (如果返回值是自身类型,赋值重载的this指针是不是本类的this指针!!!!所以需要拷贝构造)

代码示例:

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

//非指针,则深浅拷贝都一样,含有指针则内存共享,指针一致,内容一直
//深拷贝,指针不一致,内存一直,内存是独享的
//赋值重载如果有返回自身类型对象,会调用拷贝构造
//原理是:先操作一个类,再把操作的这个类拷贝到本类中,即使返回(*this),也会调用

class mystring
{
public:
    char *p;
    int n;
    mystring() :p(nullptr), n(0)
    {

    }

    mystring(char *str)
    {
        cout << "构造函数调用" << endl;
        n = strlen(str) + 1;
        p = new char[n];
        strcpy(this->p, str);//拷贝
    }

    mystring(const mystring &my)
    {
        cout << "拷贝构造函数调用" << endl;
        cout << (void *)p << endl;
        this->n = my.n;
        this->p = new char[this->n];
        strcpy(this->p, my.p);//拷贝
    }

    ////重载=
    //void operator =(const mystring &stringmy)
    //{
    //    delete this->p;
    //    cout << "赋值重载调用" << endl;
    //    this->n = stringmy.n;
    //    this->p = new char[this->n];
    //    strcpy(this->p, stringmy.p);
    //}

    //使可以多次重载
    mystring operator =(const mystring &stringmy)
    {
        cout << "赋值重载调用" << endl;
        delete this->p;
        this->n = stringmy.n;
        this->p = new char[this->n];
        cout << (void *)p << endl;
        strcpy(this->p, stringmy.p);
        return (*this);
    }

    ~mystring()
    {
        delete this->p;
    }
};

void main()
{
    mystring my1("12345");
    mystring my2,my3;
    //赋值重载
    my3 = my2 = my1;
    cout << my3.p << endl;
    cin.get();
}