📄 stdarg.h.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title><stdarg.h></title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="<stdarg.h>"></a> <a name="tag_13_45"></a><!-- <stdarg.h> --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_13_45_01"></a>NAME</h4><blockquote>stdarg.h - handle variable argument list</blockquote><h4><a name="tag_13_45_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><tt>#include <stdarg.h><br><br> void va_start(va_list</tt> <i>ap</i><tt>,</tt> <i>argN</i><tt>);<br> void va_copy(va_list</tt> <i>dest</i><tt>, va_list</tt> <i>src</i><tt>);<br> type va_arg(va_list</tt> <i>ap</i><tt>,</tt> <i>type</i><tt>);<br> void va_end(va_list</tt> <i>ap</i><tt>);<br></tt></p></blockquote><h4><a name="tag_13_45_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i><stdarg.h></i> header shall contain a set of macros which allows portable functions that accept variable argumentlists to be written. Functions that have variable argument lists (such as <a href="../functions/printf.html"><i>printf</i>()</a>)but do not use these macros are inherently non-portable, as different systems use different argument-passing conventions.</p><p>The type <b>va_list</b> shall be defined for variables used to traverse the list.</p><p>The <i>va_start</i>() macro is invoked to initialize <i>ap</i> to the beginning of the list before any calls to<i>va_arg</i>().</p><p>The <i>va_copy</i>() macro initializes <i>dest</i> as a copy of <i>src</i>, as if the <i>va_start</i>() macro had been appliedto <i>dest</i> followed by the same sequence of uses of the <i>va_arg</i>() macro as had previously been used to reach the presentstate of <i>src</i>. Neither the <i>va_copy</i>() nor <i>va_start</i>() macro shall be invoked to reinitialize <i>dest</i> withoutan intervening invocation of the <i>va_end</i>() macro for the same <i>dest</i>.</p><p>The object <i>ap</i> may be passed as an argument to another function; if that function invokes the <i>va_arg</i>() macro withparameter <i>ap</i>, the value of <i>ap</i> in the calling function is unspecified and shall be passed to the <i>va_end</i>() macroprior to any further reference to <i>ap</i>. The parameter <i>argN</i> is the identifier of the rightmost parameter in the variableparameter list in the function definition (the one just before the ...). If the parameter <i>argN</i> is declared with the<b>register</b> storage class, with a function type or array type, or with a type that is not compatible with the type that resultsafter application of the default argument promotions, the behavior is undefined.</p><p>The <i>va_arg</i>() macro shall return the next argument in the list pointed to by <i>ap</i>. Each invocation of <i>va_arg</i>()modifies <i>ap</i> so that the values of successive arguments are returned in turn. The <i>type</i> parameter shall be a type namespecified such that the type of a pointer to an object that has the specified type can be obtained simply by postfixing a<tt>'*'</tt> to type. If there is no actual next argument, or if <i>type</i> is not compatible with the type of the actual nextargument (as promoted according to the default argument promotions), the behavior is undefined, except for the following cases:</p><ul><li><p>One type is a signed integer type, the other type is the corresponding unsigned integer type, and the value is representable inboth types.</p></li><li><p>One type is a pointer to <b>void</b> and the other is a pointer to a character type.</p></li><li><p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Both types are pointers. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></li></ul><p>Different types can be mixed, but it is up to the routine to know what type of argument is expected.</p><p>The <i>va_end</i>() macro is used to clean up; it invalidates <i>ap</i> for use (unless <i>va_start</i>() or <i>va_copy</i>() isinvoked again).</p><p>Each invocation of the <i>va_start</i>() and <i>va_copy</i>() macros shall be matched by a corresponding invocation of the<i>va_end</i>() macro in the same function.</p><p>Multiple traversals, each bracketed by <i>va_start</i>() ... <i>va_end</i>(), are possible.</p></blockquote><h4><a name="tag_13_45_04"></a>EXAMPLES</h4><blockquote><p>This example is a possible implementation of <a href="../functions/execl.html"><i>execl</i>()</a>:</p><pre><tt>#include <stdarg.h><br>#define MAXARGS 31<br>/* * execl is called by * execl(file, arg1, arg2, ..., (char *)(0)); */int execl(const char *file, const char *args, ...){ va_list ap; char *array[MAXARGS +1]; int argno = 0;<br> va_start(ap, args); while (args != 0 && argno < MAXARGS) { array[argno++] = args; args = va_arg(ap, const char *); } array[argno] = (char *) 0; va_end(ap); return execv(file, array);}</tt></pre></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_13_45_05"></a>APPLICATION USAGE</h4><blockquote><p>It is up to the calling routine to communicate to the called routine how many arguments there are, since it is not alwayspossible for the called routine to determine this in any other way. For example, <a href="../functions/execl.html"><i>execl</i>()</a> is passed a null pointer to signal the end of the list. The <a href="../functions/printf.html"><i>printf</i>()</a> function can tell how many arguments are there by the <i>format</i> argument.</p></blockquote><h4><a name="tag_13_45_06"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_45_07"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_13_45_08"></a>SEE ALSO</h4><blockquote><p>The System Interfaces volume of IEEE Std 1003.1-2001, <i>exec</i>, <a href="../functions/printf.html"><i>printf</i>()</a></p></blockquote><h4><a name="tag_13_45_09"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4. Derived from the ANSI C standard.</p></blockquote><h4><a name="tag_13_45_10"></a>Issue 6</h4><blockquote><p>This reference page is updated to align with the ISO/IEC 9899:1999 standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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