How to increase the limit of “maximum open files” in C on Mac OS X

Question

The default limit for the max open files on Mac OS X is 256 (ulimit -n) and my application needs about 400 file handlers.

I tried to change the limit with setrlimit(

Answer 1

For some reason (perhaps binary compatibility), you have to define _DARWIN_UNLIMITED_STREAMS before including :

#define _DARWIN_UNLIMITED_STREAMS

#include 
#include 

main()
{
  struct rlimit rlp;

  FILE *fp[10000];
  int i;

  getrlimit(RLIMIT_NOFILE, &rlp);
  printf("before %d %d\n", rlp.rlim_cur, rlp.rlim_max);

  rlp.rlim_cur = 10000;
  setrlimit(RLIMIT_NOFILE, &rlp);

  getrlimit(RLIMIT_NOFILE, &rlp);
  printf("after %d %d\n", rlp.rlim_cur, rlp.rlim_max);

  for(i=0;i<10000;i++) {
    fp[i] = fopen("a.out", "r");
    if(fp[i]==0) { printf("failed after %d\n", i); break; }
  }

}

prints

before 256 -1
after 10000 -1
failed after 9997

This feature appears to have been introduced in Mac OS X 10.6.