C++ 中基类和派生类的析构函数

2023-09-01
四川
本文字数：1251 字
阅读完需：约 4 分钟

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：

    #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;    }

复制代码

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：

    #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;    }