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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title><varargs.h></title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_010_355"> </a>NAME</h4><blockquote>varargs.h - handle variable argument list(<b>LEGACY</b>)</blockquote><h4><a name = "tag_000_010_356"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <varargs.h>va_alistva_dclvoid va_start(pvar)va_list pvar;<i>type</i> va_arg(pvar, <i>type</i>)va_list pvar;void va_end(pvar)va_list pvar;</code></pre></blockquote><h4><a name = "tag_000_010_357"> </a>DESCRIPTION</h4><blockquote>The<i><varargs.h></i>header contains a set of macros which allowsportable procedures that accept variable argument lists to be written.Routines that have variable argument lists (such as<i><a href="printf.html">printf()</a></i>but do not use<i><varargs.h></i>are inherently non-portable, as differentmachines use different argument-passing conventions.<dl compact><dt><b>va_alist</b><dd>Used as the parameter list in a function header.<dt><b>va_dcl</b><dd>A declaration for<b>va_alist</b>.No semicolon should follow<b>va_dcl</b>.<dt><b>va_list</b><dd><index term="data type, va_list"></index>A type defined for the variable used to traverse the list.<dt><i>va_start</i>()<dd>Called to initialise<i>pvar</i>to the beginning of the list.<dt><i>va_arg</i>()<dd>Will return the next argument in the list pointed to byThe argument<i>type</i>is the type the argument is expected to be.Different types can be mixed, but it is upto the routine to know what type of argument isexpected, as it cannot be determined at run time.<dt><i>va_end</i>()<dd>Used to clean up.</dl><p>Multiple traversals, each bracketed by<i><a href="va_start.html">va_start()</a></i><i><a href="va_end.html">va_end()</a></i>,are possible.</blockquote><h4><a name = "tag_000_010_358"> </a>EXAMPLES</h4><blockquote>This example is a possible implementation of<i><a href="exec.html">execl()</a></i>.<pre><code>#include <varargs.h>#define MAXARGS 100/* execl is called by * execl(file, arg1, arg2, ..., (char *)0); */execl(va_alist)va_dcl{ va_list ap; char *file; char *args[MAXARGS]; int argno = 0; va_start(ap); file = va_arg(ap, char *); while ((args[argno++] = va_arg(ap, char *)) != (char *)0) ; va_end(ap); return execv(file, args);}</code></pre></blockquote><h4><a name = "tag_000_010_359"> </a>APPLICATION USAGE</h4><blockquote>It is up to the calling routine to specify how many argumentsthere are, since it is not always possible to determine this from thestack frame. For example,<i><a href="exec.html">execl()</a></i>is passed a zero pointer to signal the end of the list.The<i><a href="printf.html">printf()</a></i>function can tell how many arguments are there by the format.<p>It is non-portable to specify a second argument of<b>char</b>,<b>short</b>or<b>float</b>to<i><a href="va_arg.html">va_arg()</a></i>,since arguments seen by the called function are not type<b>char</b>,<b>short</b>or<b>float</b>.C language converts type<b>char</b>and<b>short</b>arguments to<b>int</b>and converts type<b>float</b>arguments to<b>double</b>before passing them to a function.<p>For backward compatibility with Issue 3, XSI-conformant systems support<i><varargs.h></i>as well as<i><a href="stdarg.h.html"><stdarg.h></a></i>.Use of<i><varargs.h></i>is not recommended.</blockquote><h4><a name = "tag_000_010_360"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_361"> </a>SEE ALSO</h4><blockquote><i><a href="exec.html">exec</a></i>,<i><a href="printf.html">printf()</a></i>,<i><a href="stdarg.h.html"><stdarg.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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