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Creating Truly Maintainable Class Factories

November 2000/Creating Truly Maintainable Class Factories/Listing 6

Listing 6: The stack calculator engine

#include <factory.h>
#include "engine.h"

#include <iostream>
#include <string>
#include <stack>
using namespace std;

#ifdef _WIN32
   string const factory_dll( "dll.dll" );
#elif defined( _DLSYM )
   string const factory_dll( "./dll" );
   #error Unsupported Platform.   Please port me

class stackimpl : public calculator_stack
      virtual void push( int i ) { m_data.push( i ); }
      virtual int pop( )
         if ( m_data.size() )
            int i = top( );
            m_data.pop( );
            return i;
         return 0;
         } // pop( )
      virtual int top( ) 
         if ( m_data.size() ) 
            return ); 
            return 0;
         } // top( )
      virtual int size( ) { return m_data.size(); }
      stack< int > m_data;
   }; // stackimpl

typedef factory< operation > op_factory;

int main( int , char** )
   stackimpl      numbers;
   string         line;
      factory( factory_dll , STRING( FACTORY_PREFIX ) );
   while( 1 )
      cin >> line;
      if ( line == "bye" )
      if ( factory.class_exists( line ) )
            object( factory.instantiate( line ) );
         cout << object->operate( &numbers ) << endl;
         int number = atoi( line.c_str() );
         numbers.push( number );

   return 0;   

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