Effective C++ 学习笔记（23）

决不要重新定义继承而来的缺省参数值

#include <iostream>
using namespace std;

enum color
{
    RED,GREEN,BLACK,WHITE
};
class Base
{
public:
virtual void ShowColor(color myColor = BLACK)
    {
        cout<<"Base Color is "<<myColor<<endl;
    }
};

class Derived:public Base
{
public:
virtual void ShowColor(color myColor = RED)
    {
        cout<<"Derived Color is    "<<myColor<<endl;
    }
};
int main()
{
    Base * B = new Derived;
    B->ShowColor();
return 0;
}

　　

运行结果：

Derived Color is 2

原因：

虚函数是动态绑定而缺省参数值是静态绑定的。