C++类继承--继承后函数的值

类的继承会首先寻找基类，若基类未实现，则会寻找派生类的函数

1. class继承，函数不继承

#include <stdio.h>

class Base
{
public:
	Base(){}
	~Base(){}

	int a;
	void setA()
	{
		a  = 1;
	}
};

class A:public Base
{
public:
	A(){}
	~A(){}

	void setA()
	{
		a  = 2;
	}

};

class B:public Base
{
public:
	B(){}
	~B(){}

	void setA()
	{
		a = 3;
	}
};

int main()
{
	A *ax = new A();
	B *bx = new B();
	Base *aClass =  ax;
	Base *bClass = bx;
	aClass->setA();
	bClass->setA();

	printf("a value of a %d\n", aClass->a);
	printf("a value of b %d\n", bClass->a);
	return 0;
}

　　运行结果：

2. 函数和Class都继承

#include <stdio.h>

class Base
{
public:
	Base(){}
	~Base(){}

	int a;
	virtual void setA()
	{
		a  = 1;
	}
};

class A:public Base
{
public:
	A(){}
	~A(){}

	virtual void setA()
	{
		a  = 2;
	}

};

class B:public Base
{
public:
	B(){}
	~B(){}

	virtual void setA()
	{
		a = 3;
	}
};

int main()
{
	A *ax = new A();
	B *bx = new B();
	Base *aClass =  ax;
	Base *bClass = bx;
	aClass->setA();
	bClass->setA();

	printf("a value of a %d\n", aClass->a);
	printf("a value of b %d\n", bClass->a);
	return 0;
}

　　运行结果：注意派生类中可以不写virtual，最好写上，以辨别是函数继承

若将2中基类的函数写为纯虚函数，运行的结果一样，但是如果基类是纯虚函数，派生类必须实现相应的函数。

class Base
{
public:
	Base(){}
	~Base(){}

	int a;
	virtual void setA()=0;

};

　　

3. 类A中不有函数，则继承自基类

class A:public Base
{
public:
	A(){}
	~A(){}

};

　结果为：