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<h5 class="subsubsection">A.2.2.1 Syntax for Variable Arguments</h5>

<p><a name="index-function-prototypes-_0028variadic_0029-3712"></a><a name="index-prototypes-for-variadic-functions-3713"></a><a name="index-variadic-function-prototypes-3714"></a>
A function that accepts a variable number of arguments must be declared
with a prototype that says so.   You write the fixed arguments as usual,
and then tack on &lsquo;<samp><span class="samp">...</span></samp>&rsquo; to indicate the possibility of
additional arguments.  The syntax of ISO&nbsp;C<!-- /@w --> requires at least one fixed
argument before the &lsquo;<samp><span class="samp">...</span></samp>&rsquo;.  For example,

<pre class="smallexample">     int
     func (const char *a, int b, ...)
     {
       ...
     }
</pre>
   <p class="noindent">defines a function <code>func</code> which returns an <code>int</code> and takes two
required arguments, a <code>const char *</code> and an <code>int</code>.  These are
followed by any number of anonymous arguments.

   <p><strong>Portability note:</strong> For some C compilers, the last required
argument must not be declared <code>register</code> in the function
definition.  Furthermore, this argument's type must be
<dfn>self-promoting</dfn>: that is, the default promotions must not change
its type.  This rules out array and function types, as well as
<code>float</code>, <code>char</code> (whether signed or not) and <code>short&nbsp;int</code><!-- /@w -->
(whether signed or not).  This is actually an ISO&nbsp;C<!-- /@w --> requirement.

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