Detailed explanation of freopen() function

Detailed explanation of freopen function and its use in OJ evaluation system

To open a binary file, add a "b" character.

redirect open

freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);

redirect recovery

• win

  freopen("CON", "r", stdin);
  freopen("CON", "w", stdout);
  

• linux

  freopen("/dev/console", "r", stdin)
   freopen("/dev/console", "w", stdout);
  

In the OJ system, common usage:

when compiling locally

#define DONLINE_JUDGE
/**
 *
 */
#ifdef DONLINE_JUDGE
	freopen("stdin.txt","r",stdin);
#endif
	ios::sync_with_stdio(false);
	cin.tie(0);

Or add it at compile time -DONLINE_JUDGE
or use Cmake to add it to CMakeLists.txtadd_compile_definitions(DONLINE_JUDGE)