gistfile1.c

#include <stdio.h>
#include <sys/param.h>
#include <sys/sysctl.h>

int
main (int argc, char **argv)
{
  int mp, mib[2] = { CTL_KERN, KERN_MAXPROC };
  size_t len = sizeof(mp);

  sysctl(mib, 2, &mp, &len, NULL, 0); 

  printf("%d\n", mp);
  return 0;
}