Can anyone please explain me the concept of #ifndef ONLINE_JUDGE

general
,
1

In many C++ and C codes i saw
#ifndef ONLINE_JUDGE

Can someone please explain me this concept and why and when is it used?

Please … . .

Thanks in Advance :slight_smile:

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2

Brother, you can get it from here : Help | CodeChef & Save time with -ONLINE_JUDGE - Codeforces

It is convenient to use the conditional directive ONLINE_JUDGE for debugging solutions.

#include <stdio.h>
int main()
{
#ifndef ONLINE_JUDGE
   freopen("input.txt", "rt", stdin);
   freopen("output.txt", "wt", stdout);
#endif
   int a, b;
   scanf("%d%d", &a, &b);
   printf("%d\n", a + b);
   return 0;
}

Note that the function freopen may also be used with stream input/output.

#include <iostream>
int main()
{
#ifndef ONLINE_JUDGE
   freopen("input.txt", "rt", stdin);
   freopen("output.txt", "wt", stdout);
#endif
   int a, b;
   std::cin >> a >> b;
   std::cout << a + b << std::endl;
   return 0;
}
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