Programming

#define _INCLUDE_POSIX_SOURCE
#define _INCLUDE_XOPEN_SOURCE
#define _INCLUDE_XOPEN_SOURCE_EXTENDED 1

sysconfPrint("_SC_SEMAPHORES", _SC_SEMAPHORES);

sysconfPrint(const char *msg, int name)
{
    long lim;

    errno = 0;
    lim = sysconf(name);
    if (lim != -1) {        /* Call succeeded, limit determinate */
        printf("%s %ld\n", msg, lim);
    } else {
        if (errno == 0)     /* Call succeeded, limit indeterminate */
            printf("%s (indeterminate)\n", msg);
        else                /* Call failed */
            errExit("sysconf %s", msg);
    }
}

If name is an invalid value, sysconf() shall return -1 and set errno to indicate the error. 
If the variable corresponding to name is described in <limits.h> as a maximum or minimum
value and the variable has no limit, sysconf() shall return -1 without changing the value 
of errno. Note that indefinite limits do not imply infinite limits; see <limits.h>.

Otherwise, sysconf() shall return the current variable value on the system. The value 
returned shall not be more restrictive than the corresponding value described to the 
application when it was compiled with the implementation's <limits.h> or <unistd.h>. The 
value shall not change during the lifetime of the calling process, [XSI] [Option Start]  
except that sysconf(_SC_OPEN_MAX) may return different values before and after a call 
to setrlimit() which changes the RLIMIT_NOFILE soft limit. [Option End]

If the variable corresponding to name is dependent on an unsupported option, the results 
are unspecified.

#include <stdio.h>
#include <unistd.h>
#include <errno.h>

main() {
  long result;

  errno = 0;
  puts("Checking NGROUPS_MAX limit");
  if ((result = sysconf(_SC_NGROUPS_MAX)) == -1)
    if (errno == 0)
      puts("NGROUPS_MAX is not supported.");
    else perror("sysconf() error");
  else
    printf("The maximum number of supplemental groups (NGROUPS_MAX) is %ld\n", result);
}