Using #undef. : ifdef « Development « C++ Tutorial

1. C++ Tutorial
2. Development
3. ifdef

#define DemoVersion
#define DOS_VERSION 5
#include <iostream>
using namespace std;

int main()
{

#ifdef DemoVersion
   cout << "DemoVersion defined.\n";
#else
   cout << "DemoVersion not defined.\n";
#endif

#ifndef DOS_VERSION
   cout << "DOS_VERSION not defined!\n";
#else
   cout << "DOS_VERSION defined as: " << DOS_VERSION << endl;
#endif

#ifdef WINDOWS_VERSION
   cout << "WINDOWS_VERSION defined!\n";
#else
   cout << "WINDOWS_VERSION was not defined.\n";
#endif

#undef DOS_VERSION

#ifdef DemoVersion
   cout << "DemoVersion defined.\n";
#else
   cout << "DemoVersion not defined.\n";
#endif

#ifndef DOS_VERSION
   cout << "DOS_VERSION not defined!\n";
#else
   cout << "DOS_VERSION defined as: " << DOS_VERSION << endl;
#endif

#ifndef WINDOWS_VERSION
   cout << "WINDOWS_VERSION defined!\n";
#else
   cout << "WINDOWS_VERSION was not defined.\n";
#endif

 cout << "Done.\n";
 return 0;

}