1 要求和区分
（1）重载要求：函数名相同，参数不同（个数、类型）、常函数也可以作为重载判断。注意返回值不是重载的判断标准。
（2）重写（即覆盖）要求：要求基类函数为虚函数，且基类函数和派生类函数名、参数等相同。
（3）隐藏（即重定义）要求：子类重新定义父类中有相同名称的非虚函数（参数列表可以不同）。
（4）重写和隐藏都是发生在基类和子类中。
2 重载代码演示
#include "stdafx.h"
#include <iostream>
/*-------------------------
// 重载
-------------------------*/
class Overload{
public:
Overload(){};
~Overload(){};
void displayNumType(int) { std::cout << " number is int " << std::endl; }
void displayNumType(short) { std::cout << " number is short " << std::endl; }
void displayNumType(double) { std::cout << " number is double " << std::endl; }
void displayNumType(int, double) { std::cout << " number1 is int, number2 is double " << std::endl; }
void displayNumType(double, int) { std::cout << " number1 is double, number2 is int " << std::endl; }
void displayNumType(int) const { std::cout << " number is int and function is const " << std::endl; }
};
int main(){
Overload r;
int num1 = 5;
short num2 = 5;
double num3 = 5;
r.displayNumType(num1);
r.displayNumType(num2);
r.displayNumType(num3);
r.displayNumType(num1, num3);
r.displayNumType(num3, num1);
const Overload r1;
r1.displayNumType(num1);
return 0;
}
结果显示：
number is int
number is short
number is double
number1 is int, number2 is double
number1 is double, number2 is int
number is int and function is const
请按任意键继续. . .
3 覆盖代码演示
#include "stdafx.h"
#include <iostream>
/*-------------------------
// 覆盖
-------------------------*/
class A{
public:
virtual void display() { std::cout << "This is Base" << std::endl; }
};
class B : public A{
public:
void display() { std::cout << "This is derived" << std::endl; }
void display1() { std::cout << "This is derived" << std::endl; }
};
int main(){
A *a = new B;
B b;
a->display();
//a->display1();
b.display();
b.display1();
}
结果显示：
This is derived
This is derived
This is derived
请按任意键继续. . .
至于为什么a->display1() 会出现错误？
因为display1()不是A的成员。
从上面的代码可以看出，覆盖（重写）主要是虚函数多态时使用，而重载也是多态的一种，两者不一样！
4 隐藏代码演示
#include "stdafx.h"
#include <iostream>
/*-------------------------
// 隐藏
-------------------------*/
class A{
public:
void display() { std::cout << "This is Base" << std::endl; }
};
class B : public A{
public:
void display() { std::cout << "This is derived" << std::endl; }
};
int main(){
A a;
B b;
a.display();
b.display();
return 0;
}
结果显示：
This is Base
This is derived
请按任意键继续. . .
备注：如果将B中的display注释掉，结果显示为：
This is Base
This is derived
