#### 31.4.3 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
         }