[C++知识库]C++ 类对象做成员与父类的构造与析构次序

类对象做成员与父类的构造与析构次序

在模拟C++考试时，经常遇上这种题目：一个派生类继承了一个父类对象，而且这个派生类中有一个类对象作为成员属性。这三个类都写了构造与析构函数，并在构造和析构时会输出相应的内容。这种题目本质上是在考察这几个类的构造和析构顺序。以下是一段简单的测试代码：

#include<iostream>
using namespace std;

class Base
{
public:
	Base()
	{
		cout << "This is constructing Base" << endl;
	}
	~Base()
	{
		cout << "This is destroying Base" << endl;
	}
};

class Member
{
public:
	Member()
	{
		cout << "This is constructing Member" << endl;
	}
	~Member()
	{
		cout << "This is destroying Member" << endl;
	}
};

class Derived : public Base //以public方式继承Base类
{
	Member m; //类对象做成员
public:
	Derived()
	{
		cout << "This is condtructing Derived" << endl;
	}
	~Derived()
	{
		cout << "This is destroying Derived" << endl;
	}
};


int main()
{
	Derived d;
	system("pause");
	return 0;
}

输出结果

This is constructing Base
This is constructing Member
This is condtructing Derived
请按任意键继续. . .
This is destroying Derived
This is destroying Member
This is destroying Base

E:\C++_projects\Learning_projects\All_test\Debug\All_test.exe (进程 16200)已退出，代码为 0。
要在调试停止时自动关闭控制台，请启用“工具”->“选项”->“调试”->“调试停止时自动关闭控制台”。
按任意键关闭此窗口. . .

所以，当一个类继承父类，且拥有一个类对象作为成员属性时，创建派生类对象会以以下顺序调用这几个类的构造函数：
父类 --> 成员类 --> 派生类
以相反的顺序析构：
派生类 --> 成员类 --> 父类
构造与析构的顺序相反是因为这几个类对象遵守出入栈原则：先进后出