Listing 1. Header File for Base Class Shape

#ifndef __SHAPE_H 
#define __SHAPE_H
#include <map> 
#include <string>
// base class for all shapes 
class shape { 
public:
   virtual void draw()=0;
};
// typedef to make it easier to set up our factory 
typedef shape *maker_t();
// our global factory 
extern map<string, maker_t *, less<string> > factory;
#endif // __SHAPE_H