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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 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 C<!-- /@w --> facility, since support |
| for ISO 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"> |
| — 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"> |
| — 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"> |
| — 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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