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 <h5 class="subsubsection">A.2.2.5 Argument Access Macros</h5>

 <p>Here are descriptions of the macros used to retrieve variable arguments.
 These macros are defined in the header file <samp><span class="file">stdarg.h</span></samp>.
 <a name="index-stdarg_002eh-3726"></a>
 <!-- stdarg.h -->
 <!-- ISO -->

 <div class="defun">
 &mdash; Data Type: <b>va_list</b><var><a name="index-va_005flist-3727"></a></var><br>
 <blockquote><p>The type <code>va_list</code> is used for argument pointer variables.
 </p></blockquote></div>

 <!-- stdarg.h -->
 <!-- ISO -->
 <div class="defun">
 &mdash; Macro: void <b>va_start</b> (<var>va_list ap, last-required</var>)<var><a name="index-va_005fstart-3728"></a></var><br>
 <blockquote><p>This macro initializes the argument pointer variable <var>ap</var> to point
 to the first of the optional arguments of the current function;
 <var>last-required</var> must be the last required argument to the function.

         <p>See <a href="Old-Varargs.html#Old-Varargs">Old Varargs</a>, for an alternate definition of <code>va_start</code>
 found in the header file <samp><span class="file">varargs.h</span></samp>.
 </p></blockquote></div>

 <!-- stdarg.h -->
 <!-- ISO -->
 <div class="defun">
 &mdash; Macro: <var>type</var> <b>va_arg</b> (<var>va_list ap, type</var>)<var><a name="index-va_005farg-3729"></a></var><br>
 <blockquote><p>The <code>va_arg</code> macro returns the value of the next optional argument,
 and modifies the value of <var>ap</var> to point to the subsequent argument.
 Thus, successive uses of <code>va_arg</code> return successive optional
 arguments.

         <p>The type of the value returned by <code>va_arg</code> is <var>type</var> as
 specified in the call.  <var>type</var> must be a self-promoting type (not
 <code>char</code> or <code>short int</code> or <code>float</code>) that matches the type
 of the actual argument.
 </p></blockquote></div>

 <!-- stdarg.h -->
 <!-- ISO -->
 <div class="defun">
 &mdash; Macro: void <b>va_end</b> (<var>va_list ap</var>)<var><a name="index-va_005fend-3730"></a></var><br>
 <blockquote><p>This ends the use of <var>ap</var>.  After a <code>va_end</code> call, further
 <code>va_arg</code> calls with the same <var>ap</var> may not work.  You should invoke
 <code>va_end</code> before returning from the function in which <code>va_start</code>
 was invoked with the same <var>ap</var> argument.

         <p>In the GNU C library, <code>va_end</code> does nothing, and you need not ever
 use it except for reasons of portability.

         </blockquote></div>

    <p>Sometimes it is necessary to parse the list of parameters more than once
 or one wants to remember a certain position in the parameter list.  To
 do this, one will have to make a copy of the current value of the
 argument.  But <code>va_list</code> is an opaque type and one cannot necessarily
 assign the value of one variable of type <code>va_list</code> to another variable
 of the same type.

 <!-- stdarg.h -->
 <!-- GNU -->
 <div class="defun">
 &mdash; Macro: void <b>__va_copy</b> (<var>va_list dest, va_list src</var>)<var><a name="index-g_t_005f_005fva_005fcopy-3731"></a></var><br>
 <blockquote><p>The <code>__va_copy</code> macro allows copying of objects of type
 <code>va_list</code> even if this is not an integral type.  The argument pointer
 in <var>dest</var> is initialized to point to the same argument as the
 pointer in <var>src</var>.

         <p>This macro is a GNU extension but it will hopefully also be available in
 the next update of the ISO C standard.
 </p></blockquote></div>

    <p>If you want to use <code>__va_copy</code> you should always be prepared for the
 possibility that this macro will not be available.  On architectures where a
 simple assignment is invalid, hopefully <code>__va_copy</code> <em>will</em> be available,
 so one should always write something like this:

 <pre class="smallexample">     {
        va_list ap, save;
        ...
      #ifdef __va_copy
        __va_copy (save, ap);
      #else
        save = ap;
      #endif
        ...
      }
 </pre>
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	<hr>
	</div>

	<h5 class="subsubsection">A.2.2.5 Argument Access Macros</h5>

	<p>Here are descriptions of the macros used to retrieve variable arguments.
	These macros are defined in the header file <samp><span class="file">stdarg.h</span></samp>.
	<a name="index-stdarg_002eh-3726"></a>
	<!-- stdarg.h -->
	<!-- ISO -->

	<div class="defun">
	— Data Type: <b>va_list</b><var><a name="index-va_005flist-3727"></a></var><br>
	<blockquote><p>The type <code>va_list</code> is used for argument pointer variables.
	</p></blockquote></div>

	<!-- stdarg.h -->
	<!-- ISO -->
	<div class="defun">
	— Macro: void <b>va_start</b> (<var>va_list ap, last-required</var>)<var><a name="index-va_005fstart-3728"></a></var><br>
	<blockquote><p>This macro initializes the argument pointer variable <var>ap</var> to point
	to the first of the optional arguments of the current function;
	<var>last-required</var> must be the last required argument to the function.

	<p>See <a href="Old-Varargs.html#Old-Varargs">Old Varargs</a>, for an alternate definition of <code>va_start</code>
	found in the header file <samp><span class="file">varargs.h</span></samp>.
	</p></blockquote></div>

	<!-- stdarg.h -->
	<!-- ISO -->
	<div class="defun">
	— Macro: <var>type</var> <b>va_arg</b> (<var>va_list ap, type</var>)<var><a name="index-va_005farg-3729"></a></var><br>
	<blockquote><p>The <code>va_arg</code> macro returns the value of the next optional argument,
	and modifies the value of <var>ap</var> to point to the subsequent argument.
	Thus, successive uses of <code>va_arg</code> return successive optional
	arguments.

	<p>The type of the value returned by <code>va_arg</code> is <var>type</var> as
	specified in the call. <var>type</var> must be a self-promoting type (not
	<code>char</code> or <code>short int</code> or <code>float</code>) that matches the type
	of the actual argument.
	</p></blockquote></div>

	<!-- stdarg.h -->
	<!-- ISO -->
	<div class="defun">
	— Macro: void <b>va_end</b> (<var>va_list ap</var>)<var><a name="index-va_005fend-3730"></a></var><br>
	<blockquote><p>This ends the use of <var>ap</var>. After a <code>va_end</code> call, further
	<code>va_arg</code> calls with the same <var>ap</var> may not work. You should invoke
	<code>va_end</code> before returning from the function in which <code>va_start</code>
	was invoked with the same <var>ap</var> argument.

	<p>In the GNU C library, <code>va_end</code> does nothing, and you need not ever
	use it except for reasons of portability.

	</blockquote></div>

	<p>Sometimes it is necessary to parse the list of parameters more than once
	or one wants to remember a certain position in the parameter list. To
	do this, one will have to make a copy of the current value of the
	argument. But <code>va_list</code> is an opaque type and one cannot necessarily
	assign the value of one variable of type <code>va_list</code> to another variable
	of the same type.

	<!-- stdarg.h -->
	<!-- GNU -->
	<div class="defun">
	— Macro: void <b>__va_copy</b> (<var>va_list dest, va_list src</var>)<var><a name="index-g_t_005f_005fva_005fcopy-3731"></a></var><br>
	<blockquote><p>The <code>__va_copy</code> macro allows copying of objects of type
	<code>va_list</code> even if this is not an integral type. The argument pointer
	in <var>dest</var> is initialized to point to the same argument as the
	pointer in <var>src</var>.

	<p>This macro is a GNU extension but it will hopefully also be available in
	the next update of the ISO C standard.
	</p></blockquote></div>

	<p>If you want to use <code>__va_copy</code> you should always be prepared for the
	possibility that this macro will not be available. On architectures where a
	simple assignment is invalid, hopefully <code>__va_copy</code> <em>will</em> be available,
	so one should always write something like this:

	<pre class="smallexample"> {
	va_list ap, save;
	...
	#ifdef __va_copy
	__va_copy (save, ap);
	#else
	save = ap;
	#endif
	...
	}
	</pre>
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