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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>confstr</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="confstr"></a> <a name="tag_03_83"></a><!-- confstr --> <!--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_03_83_01"></a>NAME</h4><blockquote>confstr - get configurable variables</blockquote><h4><a name="tag_03_83_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br><br> size_t confstr(int</tt> <i>name</i><tt>, char *</tt><i>buf</i><tt>, size_t</tt> <i>len</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_83_03"></a>DESCRIPTION</h4><blockquote><p>The <i>confstr</i>() function shall return configuration-defined string values. Its use and purpose are similar to <a href="../functions/sysconf.html"><i>sysconf</i>()</a>, but it is used where string values rather than numeric values are returned.</p><p>The <i>name</i> argument represents the system variable to be queried. The implementation shall support the following namevalues, defined in <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a>. It may support others:</p><p><br>_CS_PATH<br>_CS_POSIX_V6_ILP32_OFF32_CFLAGS<br>_CS_POSIX_V6_ILP32_OFF32_LDFLAGS<br>_CS_POSIX_V6_ILP32_OFF32_LIBS<br>_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS<br>_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS<br>_CS_POSIX_V6_ILP32_OFFBIG_LIBS<br>_CS_POSIX_V6_LP64_OFF64_CFLAGS<br>_CS_POSIX_V6_LP64_OFF64_LDFLAGS<br>_CS_POSIX_V6_LP64_OFF64_LIBS<br>_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS<br>_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS<br>_CS_POSIX_V6_LPBIG_OFFBIG_LIBS<br>_CS_POSIX_V6_WIDTH_RESTRICTED_ENVS<br><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>_CS_XBS5_ILP32_OFF32_CFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFF32_LDFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFF32_LIBS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFF32_LINTFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFFBIG_CFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFFBIG_LDFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFFBIG_LIBS (<b>LEGACY</b>)<br>_CS_XBS5_ILP32_OFFBIG_LINTFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LP64_OFF64_CFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LP64_OFF64_LDFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LP64_OFF64_LIBS (<b>LEGACY</b>)<br>_CS_XBS5_LP64_OFF64_LINTFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LPBIG_OFFBIG_CFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LPBIG_OFFBIG_LDFLAGS (<b>LEGACY</b>)<br>_CS_XBS5_LPBIG_OFFBIG_LIBS (<b>LEGACY</b>)<br>_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (<b>LEGACY</b>)<br><img src="../images/opt-end.gif" alt="[Option End]" border="0"><br></p><p>If <i>len</i> is not 0, and if <i>name</i> has a configuration-defined value, <i>confstr</i>() shall copy that value into the<i>len</i>-byte buffer pointed to by <i>buf</i>. If the string to be returned is longer than <i>len</i> bytes, including theterminating null, then <i>confstr</i>() shall truncate the string to <i>len</i>-1 bytes and null-terminate the result. Theapplication can detect that the string was truncated by comparing the value returned by <i>confstr</i>() with <i>len</i>.</p><p>If <i>len</i> is 0 and <i>buf</i> is a null pointer, then <i>confstr</i>() shall still return the integer value as definedbelow, but shall not return a string. If <i>len</i> is 0 but <i>buf</i> is not a null pointer, the result is unspecified.</p><p>If the implementation supports the POSIX shell option, the string stored in <i>buf</i> after a call to:</p><pre><tt>confstr(_CS_PATH, buf, sizeof(buf))</tt></pre><p>can be used as a value of the <i>PATH</i> environment variable that accesses all of the standard utilities ofIEEE Std 1003.1-2001, if the return value is less than or equal to <i>sizeof</i>( <i>buf</i>).</p></blockquote><h4><a name="tag_03_83_04"></a>RETURN VALUE</h4><blockquote><p>If <i>name</i> has a configuration-defined value, <i>confstr</i>() shall return the size of buffer that would be needed to holdthe entire configuration-defined value including the terminating null. If this return value is greater than <i>len</i>, the stringreturned in <i>buf</i> is truncated.</p><p>If <i>name</i> is invalid, <i>confstr</i>() shall return 0 and set <i>errno</i> to indicate the error.</p><p>If <i>name</i> does not have a configuration-defined value, <i>confstr</i>() shall return 0 and leave <i>errno</i>unchanged.</p></blockquote><h4><a name="tag_03_83_05"></a>ERRORS</h4><blockquote><p>The <i>confstr</i>() function shall fail if:</p><dl compact><dt>[EINVAL]</dt><dd>The value of the <i>name</i> argument is invalid.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_83_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_83_07"></a>APPLICATION USAGE</h4><blockquote><p>An application can distinguish between an invalid <i>name</i> parameter value and one that corresponds to a configurablevariable that has no configuration-defined value by checking if <i>errno</i> is modified. This mirrors the behavior of <a href="../functions/sysconf.html"><i>sysconf</i>()</a>.</p><p>The original need for this function was to provide a way of finding the configuration-defined default value for the environmentvariable <i>PATH .</i> Since <i>PATH</i> can be modified by the user to include directories that could contain utilities replacingthe standard utilities in the Shell and Utilities volume of IEEE Std 1003.1-2001, applications need a way to determinethe system-supplied <i>PATH</i> environment variable value that contains the correct search path for the standard utilities.</p><p>An application could use:</p><pre><tt>confstr(name, (char *)NULL, (size_t)0)</tt></pre><p>to find out how big a buffer is needed for the string value; use <a href="../functions/malloc.html"><i>malloc</i>()</a> toallocate a buffer to hold the string; and call <i>confstr</i>() again to get the string. Alternately, it could allocate a fixed,static buffer that is big enough to hold most answers (perhaps 512 or 1024 bytes), but then use <a href="../functions/malloc.html"><i>malloc</i>()</a> to allocate a larger buffer if it finds that this is too small.</p></blockquote><h4><a name="tag_03_83_08"></a>RATIONALE</h4><blockquote><p>Application developers can normally determine any configuration variable by means of reading from the stream opened by a callto:</p><pre><tt>popen("command -p getconf variable", "r");</tt></pre><p>The <i>confstr</i>() function with a <i>name</i> argument of _CS_PATH returns a string that can be used as a <i>PATH</i>environment variable setting that will reference the standard shell and utilities as described in the Shell and Utilities volume ofIEEE Std 1003.1-2001.</p><p>The <i>confstr</i>() function copies the returned string into a buffer supplied by the application instead of returning apointer to a string. This allows a cleaner function in some implementations (such as those with lightweight threads) and resolvesquestions about when the application must copy the string returned.</p></blockquote><h4><a name="tag_03_83_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_83_10"></a>SEE ALSO</h4><blockquote><p><a href="pathconf.html"><i>pathconf</i>()</a> , <a href="sysconf.html"><i>sysconf</i>()</a> , the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a>, the Shell and Utilities volume ofIEEE Std 1003.1-2001, <a href="../utilities/c99.html"><i>c99</i></a></p></blockquote><h4><a name="tag_03_83_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4. Derived from the ISO POSIX-2 standard.</p></blockquote><h4><a name="tag_03_83_12"></a>Issue 5</h4><blockquote><p>A table indicating the permissible values of <i>name</i> is added to the DESCRIPTION. All those marked EX are new in thisissue.</p></blockquote><h4><a name="tag_03_83_13"></a>Issue 6</h4><blockquote><p>The Open Group Corrigendum U033/7 is applied. The return value for the case returning the size of the buffer now explicitlystates that this includes the terminating null.</p><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>The DESCRIPTION is updated with new arguments which can be used to determine configuration strings for C compiler flags,linker/loader flags, and libraries for each different supported programming environment. This is a change to support data sizeneutrality.</p></li></ul><p>The following changes were made to align with the IEEE P1003.1a draft standard:</p><ul><li><p>The DESCRIPTION is updated to include text describing how _CS_PATH can be used to obtain a <i>PATH</i> to access the standardutilities.</p></li></ul><p>The macros associated with the <i>c89</i> programming models are marked LEGACY and new equivalent macros associated with <ahref="../utilities/c99.html"><i>c99</i></a> are introduced.</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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