Where is the PIPE_BUF constant defined?

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main() {
  printf("%d\n",PIPE_BUF); //I have to include some header file to make this constant available... But which one?
  return 0;
}

---

Thank you in advance.

Depends on the O/S but for Unix types try limits.h

Yeah, I'm using Ubuntu Linux right now. Including limits.h did the trick. Thanks.