#### 33.4.3 Examples of `sysconf` ¶

We recommend that you first test for a macro definition for the parameter you are interested in, and call `sysconf` only if the macro is not defined. For example, here is how to test whether job control is supported:

    int
    have_job_control (void)
    {
    #ifdef _POSIX_JOB_CONTROL
      return 1;
    #else
      int value = sysconf (_SC_JOB_CONTROL);
      if (value < 0)
        /* If the system is that badly wedged,
           there’s no use trying to go on.  */
        fatal (strerror (errno));
      return value;
    #endif
    }

Here is how to get the value of a numeric limit:

    int
    get_child_max ()
    {
    #ifdef CHILD_MAX
      return CHILD_MAX;
    #else
      int value = sysconf (_SC_CHILD_MAX);
      if (value < 0)
        fatal (strerror (errno));
      return value;
    #endif
    }