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<h5 class="subsubsection">A.2.3.1 Old-Style Variadic Functions</h5>

<p><a name="index-varargs_002eh-3732"></a>Before ISO&nbsp;C<!-- /@w -->, programmers used a slightly different facility for
writing variadic functions.  The GNU C compiler still supports it;
currently, it is more portable than the ISO&nbsp;C<!-- /@w --> facility, since support
for ISO&nbsp;C<!-- /@w --> is still not universal.  The header file which defines the
old-fashioned variadic facility is called <samp><span class="file">varargs.h</span></samp>.

   <p>Using <samp><span class="file">varargs.h</span></samp> is almost the same as using <samp><span class="file">stdarg.h</span></samp>. 
There is no difference in how you call a variadic function;
see <a href="Calling-Variadics.html#Calling-Variadics">Calling Variadics</a>.  The only difference is in how you define
them.  First of all, you must use old-style non-prototype syntax, like
this:

<pre class="smallexample">     tree
     build (va_alist)
          va_dcl
     {
</pre>
   <p>Secondly, you must give <code>va_start</code> only one argument, like this:

<pre class="smallexample">       va_list p;
       va_start (p);
</pre>
   <p>These are the special macros used for defining old-style variadic
functions:

<!-- varargs.h -->
<!-- Unix -->
<div class="defun">
&mdash; Macro: <b>va_alist</b><var><a name="index-va_005falist-3733"></a></var><br>
<blockquote><p>This macro stands for the argument name list required in a variadic
function. 
</p></blockquote></div>

<!-- varargs.h -->
<!-- Unix -->
<div class="defun">
&mdash; Macro: <b>va_dcl</b><var><a name="index-va_005fdcl-3734"></a></var><br>
<blockquote><p>This macro declares the implicit argument or arguments for a variadic
function. 
</p></blockquote></div>

<!-- varargs.h -->
<!-- Unix -->
<div class="defun">
&mdash; Macro: void <b>va_start</b> (<var>va_list ap</var>)<var><a name="index-va_005fstart-3735"></a></var><br>
<blockquote><p>This macro, as defined in <samp><span class="file">varargs.h</span></samp>, initializes the argument
pointer variable <var>ap</var> to point to the first argument of the current
function. 
</p></blockquote></div>

   <p>The other argument macros, <code>va_arg</code> and <code>va_end</code>, are the same
in <samp><span class="file">varargs.h</span></samp> as in <samp><span class="file">stdarg.h</span></samp>; see <a href="Argument-Macros.html#Argument-Macros">Argument Macros</a>, for
details.

   <p>It does not work to include both <samp><span class="file">varargs.h</span></samp> and <samp><span class="file">stdarg.h</span></samp> in
the same compilation; they define <code>va_start</code> in conflicting ways.

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