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<h4 class="subsection">31.4.3 Examples of <code>sysconf</code></h4>

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

<pre class="smallexample">     int
     have_job_control (void)
     {
     #ifdef _POSIX_JOB_CONTROL
       return 1;
     #else
       int value = sysconf (_SC_JOB_CONTROL);
       if (value &lt; 0)
         /* <span class="roman">If the system is that badly wedged,</span>
            <span class="roman">there's no use trying to go on.</span>  */
         fatal (strerror (errno));
       return value;
     #endif
     }
</pre>
   <p>Here is how to get the value of a numeric limit:

<pre class="smallexample">     int
     get_child_max ()
     {
     #ifdef CHILD_MAX
       return CHILD_MAX;
     #else
       int value = sysconf (_SC_CHILD_MAX);
       if (value &lt; 0)
         fatal (strerror (errno));
       return value;
     #endif
     }
</pre>
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