缺省参数是编译期间绑定的,而不是动态绑定

#include <iostream>
using namespace std;

class A
{
public:
	virtual void Fun(int number = 10)
	{
		std::cout << "A::Fun with number " << number<<endl;
	}
};

class B: public A
{
public:
	virtual void Fun(int number = 20)
	{
		std::cout << "B::Fun with number " << number<<endl;
	}
};

int main()
{
	B b;
	A &a = b;
	a.Fun();
	return 0;
}                 //虚函数动态绑定=>B，非A，缺省实参是编译时候确定的=>10，非20