#5_ver2.cpp

c++编程的几个小例子

#include <stdio.h>

class animal {
     public:
          virtual void identify() { printf("%s\n", "animal"); }
};

class mammal : public animal {
     public:
          void identify() { printf("%s\n", "mammal"); }
};

class bird : public animal {
     public:
          void identify() { printf("%s\n", "bird"); }
};

class dog : public mammal {
     public:
          void identify() { printf("%s\n", "dog"); }
};

class eagle : public bird {
     public:
          void identify() { printf("%s\n", "eagle"); }
};

void print1(void), print2(void), print3(void);

main()
{
     print1();
     print2();
     print3();
}

void print1()
{
     animal *ap = new animal;    ap->identify();
     mammal *mp = new mammal;    mp->identify();
     bird   *bp = new bird;      bp->identify();
     dog    *dp = new dog;       dp->identify();
     eagle  *ep = new eagle;     ep->identify();

     printf("\n");
}

void print2()
{
     animal *ap = new animal;
     ap->identify();                    

     ((mammal *) ap)->identify();          
     mammal *mp = (mammal *) ap;
     mp->identify();                    

     printf("\n");
}

void print3()
{
     animal a, *ap = &a;
     mammal m;
     eagle  e;

     ap->identify();
     
     ap = &m;
     ap->identify();

     printf("\n");
}

/* output:

animal
mammal
bird
dog
eagle

animal
animal
animal

animal
mammal

*/