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
#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
#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。