C++拷贝赋值operator=

拷贝赋值：两个对象之间的拷贝

默认拷贝赋值导致错误

#include <iostream>
class A {
public:
    A(int i=10){
        m_pi = new int(i);
        ii = i;
        
    }
    A(const A& that) {  
        std::cout << "深拷贝构造函数" << std::endl;
        m_pi = new int;  
        *m_pi = *that.m_pi;    
    }
    void print(void) {
        std::cout << ii << std::endl;
    }
    ~A(void) {
        
        std::cout << "xigouhansu："<<this << std::endl;
        delete m_pi;
    }
private:
    int* m_pi;
    int ii;
    
};

int main()
{
    A a(100);
    A b;
    b.print();
    //b.operator=(a);
    b = a;//拷贝赋值；与b.operator=(a)等价
    //拷贝赋值：两个对象已经存在
    //编译器其实执行函数：b.operator=(a);
    //如果程序没写这个函数，会执行默认的，在执行析构函数时导致程序中断
    //中断原因:默认的拷贝赋值是直接拷贝各个成员变量值；由于m_pi是指针，a和b指向同一个堆区数据，不能delete两次
    //所以当存在指针类型的成员变量时，要自己写b.operator=(a)函数
    b.print();
    
    
}

 

自写拷贝赋值函数

#include <iostream>
class A {
public:
    A(int i=10){
        m_pi = new int(i);
        ii = i;
        
    }
    A(const A& that) {  
        std::cout << "senkaobei" << std::endl;
        m_pi = new int;  
        *m_pi = *that.m_pi;    
    }
    A& operator=(const A&that) {   //自写拷贝赋值函数
        if (&that != this) {  //防止自赋值
            *m_pi = *that.m_pi;  //拷贝指针的数据
            ii = that.ii;
        }
        return *this;    //返回自身引用
    }
    void print(void) {
        std::cout << ii << std::endl;
        std::cout << *m_pi << std::endl;
    }
    ~A(void) {
        
        std::cout << "xigouhansu："<<this << std::endl;
        delete m_pi;
    }
private:
    int* m_pi;
    int ii;
    
};

int main()
{
    A a(100);
    A b;

    b.print();
    b = a;   //拷贝赋值
     std::cout << &a << std::endl;
    std::cout << &b << std::endl;
    b.print();
    
    
}