C++概念整理

  1 /*
  2     面向对象:
  3             多态,
  4             继承
  5             封装
  6 */
  7 #include <stdio.h>
  8 #include <stdlib.h>
  9 
 10 //一旦有了纯虚函数,该对象就不能实例化了.
 11 #define USE_PURE_VIRTUAL_FUNC 1
 12 
 13 class CBase
 14 {
 15 public:
 16     CBase(){}
 17     ~CBase(){}
 18 public:
 19     void doA()//不标virtual,说明不想被子类重载,如果遇到基类对象指针,则使用该函数时永远是用基类的
 20     {
 21         printf("call %s
",__FUNCTION__);
 22     }
 23     virtual void doB()
 24     {
 25         printf("call %s
",__FUNCTION__);
 26     }
 27 #if USE_PURE_VIRTUAL_FUNC > 0
 28     virtual void doC() = 0;//父类不实现,但子类必须实现.
 29 #endif    
 30     
 31 };
 32 
 33 class CChild:public CBase
 34 {
 35 public:
 36     CChild():CBase()
 37     {};
 38     ~CChild(){};
 39 public:
 40     void doA()
 41     {
 42         printf("child call doA
");
 43     }
 44     virtual void doB()
 45     {
 46         printf("child call doB
");
 47     }
 48 #if USE_PURE_VIRTUAL_FUNC > 0    
 49     virtual void doC()
 50     {
 51         printf("child call doC
");
 52     }
 53 #endif    
 54 };
 55 
 56 int main(void)
 57 {
 58 #if USE_PURE_VIRTUAL_FUNC <= 0    
 59     CBase* pB = new CBase();
 60     CChild* pC = new CChild();
 61     
 62     
 63     pB->doA();
 64     pB->doB();
 65     
 66     pC->doA();
 67     pC->doB();
 68     
 69     
 70     CBase* pTemp = pB;
 71     pTemp->doA();
 72     pTemp->doB();
 73     
 74     
 75     pTemp = pC;
 76     pTemp->doA();
 77     pTemp->doB();
 78     
 79     delete pB;
 80     delete pC;
 81 #else
 82     CChild* pC = new CChild();
 83     
 84     
 85     pC->doA();
 86     pC->doB();
 87     
 88     
 89     CBase* pTemp = NULL;
 90     pTemp = pC;
 91     pTemp->doA();
 92     pTemp->doB();    
 93     pTemp->doC();    
 94     
 95     delete pC;
 96 #endif
 97 
 98     
 99     
100     
101     return 0;
102 }