C++中基类和派生类的析构函数

向阳逐梦2023-09-01 22:16

和构造函数类似，析构函数也不能被继承。与构造函数不同的是，在派生类的析构函数中不用显式地调用基类的析构函数，因为每个类只有一个析构函数，编译器知道如何选择，无需程序员干涉。

另外析构函数的执行顺序和构造函数的执行顺序也刚好相反：

创建派生类对象时，构造函数的执行顺序和继承顺序相同，即先执行基类构造函数，再执行派生类构造函数。
而销毁派生类对象时，析构函数的执行顺序和继承顺序相反，即先执行派生类析构函数，再执行基类析构函数。

具体看实例：

c 复制代码

    #include <iostream>
    using namespace std;
    class A{
    public:
        A(){cout<<"A constructor"<<endl;}
        ~A(){cout<<"A destructor"<<endl;}
    };
    class B: public A{
    public:
        B(){cout<<"B constructor"<<endl;}
        ~B(){cout<<"B destructor"<<endl;}
    };
    class C: public B{
    public:
        C(){cout<<"C constructor"<<endl;}
        ~C(){cout<<"C destructor"<<endl;}
    };
    int main(){
        C test;
        return 0;
    }

运行结果：

A constructor

B constructor

C constructor

C destructor

B destructor

A destructor

下面是一个多继承的实例：

c 复制代码

    #include <iostream>
    using namespace std;
    //基类
    class BaseA{
    public:
        BaseA(int a, int b);
        ~BaseA();
    protected:
        int m_a;
        int m_b;
    };
    BaseA::BaseA(int a, int b): m_a(a), m_b(b){
        cout<<"BaseA constructor"<<endl;
    }
    BaseA::~BaseA(){
        cout<<"BaseA destructor"<<endl;
    }
    //基类
    class BaseB{
    public:
        BaseB(int c, int d);
        ~BaseB();
    protected:
        int m_c;
        int m_d;
    };
    BaseB::BaseB(int c, int d): m_c(c), m_d(d){
        cout<<"BaseB constructor"<<endl;
    }
    BaseB::~BaseB(){
        cout<<"BaseB destructor"<<endl;
    }
    //派生类
    class Derived: public BaseA, public BaseB{
    public:
        Derived(int a, int b, int c, int d, int e);
        ~Derived();
    public:
        void show();
    private:
        int m_e;
    };
    Derived::Derived(int a, int b, int c, int d, int e): BaseA(a, b), BaseB(c, d), m_e(e){
        cout<<"Derived constructor"<<endl;
    }
    Derived::~Derived(){
        cout<<"Derived destructor"<<endl;
    }
    void Derived::show(){
        cout<<m_a<<", "<<m_b<<", "<<m_c<<", "<<m_d<<", "<<m_e<<endl;
    }
    int main(){
        Derived obj(1, 2, 3, 4, 5);
        obj.show();
        return 0;
    }

运行结果：

BaseA constructor

BaseB constructor

Derived constructor

1, 2, 3, 4, 5

Derived destructor

BaseB destructorBase

A destructor

从运行结果中还可以发现，多继承形式下析构函数的执行顺序和构造函数的执行顺序相反。