定义一个基类BaseClass，从它派生出类DerivedClass,BaseClass有成员函数fn1()、fn2()，DerivedClass也有成员函数fn1()和fn2()，在主函数中声明一个DerivedClass对象，分别用DerivedClass的对象以及BaseClass和DerivedClass的指针来调用fn1()、fn2()，观察运行结果。
1 #include <iostream.h>
2 class BaseClass {
3 public: void fn1(); void fn2();
4 };
5 void BaseClass::fn1() {
6 cout << "调用基类的函数fn1()" << endl;
7 }
8 void BaseClass::fn2() {
9 cout << "调用基类的函数fn2()" << endl;
10 }
11 class DerivedClass : public BaseClass {
12 public:
13 void fn1(); void fn2(); };
14 void DerivedClass::fn1() {
15 cout << "调用派生类的函数fn1()" << endl;
16 }
17 void DerivedClass::fn2() {
18 cout << "调用派生类的函数fn2()" << endl;
19 }
20 void main()
21 {
22 DerivedClass aDerivedClass;
23 DerivedClass *pDerivedClass = &aDerivedClass;
24 BaseClass *pBaseClass = &aDerivedClass;
25 aDerivedClass.fn1();
26 aDerivedClass.fn2();
27 pBaseClass->fn1();
28 pBaseClass->fn2();
29 pDerivedClass->fn1();
30 pDerivedClass->fn2();
31 }
