深入理解C++的多态性

#include<iostream>
using namespace std;
class A
{
public:
 void foo()
 {
  printf("1/n");
 }
 virtual void fun()
 {
  printf("2/n");
 }
};
class B : public A
{
public:
 void foo()
 {
  printf("3/n");
 }
 void fun()
 {
  printf("4/n");
 }
};
int main(void)
{
 A a;

 A *p = &a;
 p->foo();
 p->fun();
 p = &b;
 p->foo();
 p->fun();
 return 0;
}

//小结：1、有virtual才可能发生多态现象
// 2、不发生多态（无virtual）调用就按原类型调用
#include<iostream>
using namespace std;
class Base
{
public:
 virtual void f(float x)
 {
  cout<<"Base::f(float)"<< x <<endl;
 }
 void g(float x)
 {
  cout<<"Base::g(float)"<< x <<endl;
 }
 void h(float x)
 {
  cout<<"Base::h(float)"<< x <<endl;
 }
};
class Derived : public Base
{
public:
 virtual void f(float x)
 {
  cout<<"Derived::f(float)"<< x <<endl;   //多态、覆盖
 }
 void g(int x)
 {
  cout<<"Derived::g(int)"<< x <<endl;     //隐藏
 }
 void h(float x)
 {
  cout<<"Derived::h(float)"<< x <<endl;   //隐藏
 }
};
int main(void)
{
 Derived d;
 Base *pb = &d;
 Derived *pd = &d;
 // Good : behavior depends solely on type of the object
 pb->f(3.14f);   // Derived::f(float) 3.14
 pd->f(3.14f);   // Derived::f(float) 3.14
 // Bad : behavior depends on type of the pointer
 pb->g(3.14f);   // Base::g(float)  3.14
 pd->g(3.14f);   // Derived::g(int) 3
 // Bad : behavior depends on type of the pointer
 pb->h(3.14f);   // Base::h(float) 3.14
 pd->h(3.14f);   // Derived::h(float) 3.14
 return 0;
}