C++：继承性

一、基本概念

• 一个基类可以派生多个派生类，一个派生类也可以由多个基类派生而成
• 继承
  • 单一继承
  • 多重继承
• 继承方式（缺省默认：private）
  • public
  • private
  • protected

	公有继承	保护继承	私有继承
公有成员	public	protected	private
保护成员	protected	protected	private
私有成员	不可见	不可见	不可见

• 基类的 private 成员不可以被继承

二、派生类的构造及析构

#include <iostream>
using namespace std;

class a1
{
public:
    a1()
    {
        cout << "a1 Constructor called" << endl;
    }
    ~a1()
    {
        cout << "a1 Destructor called" << endl;
    }
};

class a2
{
public:
    a2()
    {
        cout << "a2 Constructor called" << endl;
    }
    ~a2()
    {
        cout << "a2 Destructor called" << endl;
    }
};

class Derived : public a1, public a2
{
public:
    Derived()
    {
        cout << "Derived Constructor called" << endl;
    }
    ~Derived()
    {
        cout << "Derived Destructor called" << endl;
    }
};

int main()
{
    Derived obj;
    return 0;
}

输出结果：

a1 Constructor called
a2 Constructor called
Derived Constructor called
Derived Destructor called
a2 Destructor called
a1 Destructor called 

在定义一个派生类对象时，构造函数的调用顺序：

        基类 >>> 派生类对象成员（按定义顺序） >>> 派生类

析构函数调用顺序恰好相反

//将 Derived 修改如下
class Derived : pu