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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>opendir</title></head><body bgcolor="white"><basefont size="3"> <a name="opendir"></a> <a name="tag_03_411"></a><!-- opendir --> <!--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_411_01"></a>NAME</h4><blockquote>opendir - open a directory</blockquote><h4><a name="tag_03_411_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/dirent.h.html">dirent.h</a>><br><br> DIR *opendir(const char *</tt><i>dirname</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_411_03"></a>DESCRIPTION</h4><blockquote><p>The <i>opendir</i>() function shall open a directory stream corresponding to the directory named by the <i>dirname</i> argument.The directory stream is positioned at the first entry. If the type <b>DIR</b> is implemented using a file descriptor, applicationsshall only be able to open up to a total of {OPEN_MAX} files and directories.</p></blockquote><h4><a name="tag_03_411_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>opendir</i>() shall return a pointer to an object of type <b>DIR</b>. Otherwise, a null pointershall be returned and <i>errno</i> set to indicate the error.</p></blockquote><h4><a name="tag_03_411_05"></a>ERRORS</h4><blockquote><p>The <i>opendir</i>() function shall fail if:</p><dl compact><dt>[EACCES]</dt><dd>Search permission is denied for the component of the path prefix of <i>dirname</i> or read permission is denied for<i>dirname</i>.</dd><dt>[ELOOP]</dt><dd>A loop exists in symbolic links encountered during resolution of the <i>dirname</i> argument.</dd><dt>[ENAMETOOLONG]</dt><dd>The length of the <i>dirname</i> argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.</dd><dt>[ENOENT]</dt><dd>A component of <i>dirname</i> does not name an existing directory or <i>dirname</i> is an empty string.</dd><dt>[ENOTDIR]</dt><dd>A component of <i>dirname</i> is not a directory.</dd></dl><p>The <i>opendir</i>() function may fail if:</p><dl compact><dt>[ELOOP]</dt><dd>More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the <i>dirname</i> argument.</dd><dt>[EMFILE]</dt><dd>{OPEN_MAX} file descriptors are currently open in the calling process.</dd><dt>[ENAMETOOLONG]</dt><dd>As a result of encountering a symbolic link in resolution of the <i>dirname</i> argument, the length of the substituted pathnamestring exceeded {PATH_MAX}.</dd><dt>[ENFILE]</dt><dd>Too many files are currently open in the system.</dd></dl><br></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_411_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_411_06_01"></a>Open a Directory Stream</h5><p>The following program fragment demonstrates how the <i>opendir</i>() function is used.</p><pre><tt>#include <sys/types.h>#include <dirent.h>#include <libgen.h>... DIR *dir; struct dirent *dp;... if ((dir = opendir (".")) == NULL) { perror ("Cannot open ."); exit (1); }<br> while ((dp = readdir (dir)) != NULL) {...</tt></pre></blockquote><h4><a name="tag_03_411_07"></a>APPLICATION USAGE</h4><blockquote><p>The <i>opendir</i>() function should be used in conjunction with <a href="../functions/readdir.html"><i>readdir</i>()</a>, <ahref="../functions/closedir.html"><i>closedir</i>()</a>, and <a href="../functions/rewinddir.html"><i>rewinddir</i>()</a> toexamine the contents of the directory (see the EXAMPLES section in <a href="readdir.html"><i>readdir</i>()</a> ). This method isrecommended for portability.</p></blockquote><h4><a name="tag_03_411_08"></a>RATIONALE</h4><blockquote><p>Based on historical implementations, the rules about file descriptors apply to directory streams as well. However, this volumeof IEEE Std 1003.1-2001 does not mandate that the directory stream be implemented using file descriptors. The descriptionof <a href="../functions/closedir.html"><i>closedir</i>()</a> clarifies that if a file descriptor is used for the directory stream,it is mandatory that <a href="../functions/closedir.html"><i>closedir</i>()</a> deallocate the file descriptor. When a filedescriptor is used to implement the directory stream, it behaves as if the FD_CLOEXEC had been set for the file descriptor.</p><p>The directory entries for dot and dot-dot are optional. This volume of IEEE Std 1003.1-2001 does not provide a way totest <i>a priori</i> for their existence because an application that is portable must be written to look for (and usually ignore)those entries. Writing code that presumes that they are the first two entries does not always work, as many implementations permitthem to be other than the first two entries, with a "normal" entry preceding them. There is negligible value in providing a wayto determine what the implementation does because the code to deal with dot and dot-dot must be written in any case and becausesuch a flag would add to the list of those flags (which has proven in itself to be objectionable) and might be abused.</p><p>Since the structure and buffer allocation, if any, for directory operations are defined by the implementation, this volume ofIEEE Std 1003.1-2001 imposes no portability requirements for erroneous program constructs, erroneous data, or the use ofunspecified values such as the use or referencing of a <i>dirp</i> value or a <b>dirent</b> structure value after a directorystream has been closed or after a <a href="../functions/fork.html"><i>fork</i>()</a> or one of the <i><a href="../functions/exec.html">exec</a></i> function calls.</p></blockquote><h4><a name="tag_03_411_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_411_10"></a>SEE ALSO</h4><blockquote><p><a href="closedir.html"><i>closedir</i>()</a> , <a href="lstat.html"><i>lstat</i>()</a> , <a href="readdir.html"><i>readdir</i>()</a> , <a href="rewinddir.html"><i>rewinddir</i>()</a> , <a href="symlink.html"><i>symlink</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/dirent.h.html"><i><dirent.h></i></a>,<a href="../basedefs/limits.h.html"><i><limits.h></i></a>, <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a></p></blockquote><h4><a name="tag_03_411_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_03_411_12"></a>Issue 6</h4><blockquote><p>In the SYNOPSIS, the optional include of the <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> header isremoved.</p><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>The requirement to include <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> has been removed. Although <ahref="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> was required for conforming implementations of previous POSIXspecifications, it was not required for UNIX applications.</p></li><li><p>The [ELOOP] mandatory error condition is added.</p></li><li><p>A second [ENAMETOOLONG] is added as an optional error condition.</p></li></ul><p>The following changes were made to align with the IEEE P1003.1a draft standard:</p><ul><li><p>The [ELOOP] optional error condition is added.</p></li></ul></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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