C: 面向对象（3）

以下代码演示如何用C来模拟多态。gcc版本：3.4.4
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>
#ifndef class
        #define class struct
#endif
#ifndef private
        #define private
#endif
#ifndef public
        #define public
#endif
#ifndef protected
        #define protected
#endif
#ifndef bool
        #define bool int
#endif
#ifndef true
        #define true 1
#endif
#ifndef false
        #define false 0
#endif
class Parent{
      //private members
      private class Parent *this;
      private size_t len;
     
      //public members
      public size_t (*length)(class Parent *this);
      public void (*construct)(class Parent *this);
      public void (*print)(class Parent *this);
      public void (*destruct)(class Parent *this);
};
class Son{
      //private members
      private class Son *this;
      //inherit
      private class Parent *inherit;
     
      //public members
      public size_t (*length)(class Son *this);
      public bool (*construct)(class Son *this);
      public void (*print)(class Son *this);
      public void (*destruct)(class Son *this);
};
//forward declaration
void ParentConstruct(class Parent *this);
void ParentPr