2.5.5.2.c

#include "apue.h"
#include <errno.h>
#include <limits.h>

#ifdef OPEN_MAX
static long openmax = OPEN_MAX;
#else
static long openmax = 0;
#endif

#define OPEN_MAX_GUESS 256

long open_max() {
    if (openmax == 0) {
        errno = 0;
        if ((openmax = sysconf(_SC_OPEN_MAX)) < 0) {
            if (errno == 0)
                openmax = OPEN_MAX_GUESS;
            else
                err_sys("sysconf error for _SC_OPEN_MAX");
        }
    }
    return (openmax);
}

int main() {
    printf("%ld\n", open_max());
    return 0;
}