C++子类的拷贝构造和拷贝赋值

子类拷贝构造函数 

#include<iostream>

class Base { 
public:
    Base(int i = 0) :m_i(i) { }
    Base(const Base& that) :m_i(that.m_i) {  //基类拷贝构造
        std::cout << "基类拷贝构造函数" << '
';
    }
    int m_i;
  
 };

class Derived :public Base {
public:
    Derived(int i=0,int j=0):Base(i),m_j(j){}
    Derived(const Derived& that) :Base(that),m_j(that.m_j) {  //子类拷贝构造函数
        //Base(that)   执行基类拷贝构造函数
        std::cout << "子类拷贝构造函数" << '
';
    }
    int m_j;
};

int main()
{
    Derived d(100, 200);
    Derived dd = d;  //拷贝构造
    
    std::cout << d.m_i << ",    " << d.m_j << std::endl;
    std::cout << dd.m_i << ",    " << dd.m_j << std::endl;

    return 0;
}

如果子类没有定义拷贝构造函数，那么编译器会提供缺省的拷贝构造函数，该函数会自动调用基类的拷贝构造函数 

子类拷贝赋值函数

#include<iostream>

class Base { 
public:
    Base(int i = 0) :m_i(i) { }
    Base& operator=(const Base& that) { //基类拷贝赋值
        std::cout << "基类拷贝赋值" << std::endl;
        if (&that != this) {   //防止自赋值
            m_i = that.m_i;  
        }
        return *this;
    }
    int m_i;
  
 };

class Derived :public Base {
public:
    Derived(int i=0,int j=0):Base(i),m_j(j){}
    Derived& operator=(const Derived& that) { //子类拷贝赋值
        std::cout << "子类拷贝赋值" << std::endl;
        if (&that != this) {   //防止自赋值
            Base::operator=(that);  //执行基类拷贝赋值函数
            m_j = that.m_j;
        }
        return *this;
    }
    
    int m_j;
};

int main()
{
    Derived d(100, 200);
    Derived dd;
    dd = d;

    std::cout << dd.m_i << "     " << dd.m_j << std::endl;

    return 0;
}

如果子类没有定义拷贝赋值函数，那么编译器会提供缺省的拷贝赋值函数，该函数会自动调用基类的拷贝赋值函数