380 lines
16 KiB
HTML
380 lines
16 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>fopen</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="fopen"></a> <a name="tag_03_176"></a><!-- fopen -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_176_01"></a>NAME</h4>
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<blockquote>fopen - open a stream</blockquote>
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<h4><a name="tag_03_176_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/stdio.h.html">stdio.h</a>><br>
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<br>
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FILE *fopen(const char *restrict</tt> <i>filename</i><tt>, const char *restrict</tt> <i>mode</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_176_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>The <i>fopen</i>() function shall open the file whose pathname is the string pointed to by <i>filename</i>, and associates a
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stream with it.</p>
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<p>The <i>mode</i> argument points to a string. If the string is one of the following, the file shall be opened in the indicated
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mode. Otherwise, the behavior is undefined.</p>
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<dl compact>
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<dt><i>r</i> or <i>rb</i></dt>
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<dd>Open file for reading.</dd>
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<dt><i>w</i> or <i>wb</i></dt>
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<dd>Truncate to zero length or create file for writing.</dd>
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<dt><i>a</i> or <i>ab</i></dt>
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<dd>Append; open or create file for writing at end-of-file.</dd>
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<dt><i>r+</i> or <i>rb+</i> or <i>r+b</i></dt>
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<dd>Open file for update (reading and writing).</dd>
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<dt><i>w+</i> or <i>wb+</i> or <i>w+b</i></dt>
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<dd>Truncate to zero length or create file for update.</dd>
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<dt><i>a+</i> or <i>ab+</i> or <i>a+b</i></dt>
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<dd>Append; open or create file for update, writing at end-of-file.</dd>
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</dl>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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character <tt>'b'</tt> shall have no effect, but is allowed for ISO C standard conformance. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"> Opening a file with read mode (<i>r</i> as the first character in the <i>mode</i> argument) shall
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fail if the file does not exist or cannot be read.</p>
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<p>Opening a file with append mode (<i>a</i> as the first character in the <i>mode</i> argument) shall cause all subsequent writes
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to the file to be forced to the then current end-of-file, regardless of intervening calls to <a href=
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"../functions/fseek.html"><i>fseek</i>()</a>.</p>
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<p>When a file is opened with update mode ( <tt>'+'</tt> as the second or third character in the <i>mode</i> argument), both input
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and output may be performed on the associated stream. However, the application shall ensure that output is not directly followed by
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input without an intervening call to <a href="../functions/fflush.html"><i>fflush</i>()</a> or to a file positioning function ( <a
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href="../functions/fseek.html"><i>fseek</i>()</a>, <a href="../functions/fsetpos.html"><i>fsetpos</i>()</a>, or <a href=
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"../functions/rewind.html"><i>rewind</i>()</a>), and input is not directly followed by output without an intervening call to a file
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positioning function, unless the input operation encounters end-of-file.</p>
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<p>When opened, a stream is fully buffered if and only if it can be determined not to refer to an interactive device. The error and
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end-of-file indicators for the stream shall be cleared.</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If
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<i>mode</i> is <i>w</i>, <i>wb</i>, <i>a</i>, <i>ab</i>, <i>w</i>+, <i>wb</i>+, <i>w</i>+<i>b</i>, <i>a</i>+, <i>ab</i>+, or
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<i>a</i>+<i>b</i>, and the file did not previously exist, upon successful completion, the <i>fopen</i>() function shall mark for
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update the <i>st_atime</i>, <i>st_ctime</i>, and <i>st_mtime</i> fields of the file and the <i>st_ctime</i> and <i>st_mtime</i>
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fields of the parent directory.</p>
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<p>If <i>mode</i> is <i>w</i>, <i>wb</i>, <i>w</i>+, <i>wb</i>+, or <i>w</i>+<i>b</i>, and the file did previously exist, upon
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successful completion, <i>fopen</i>() shall mark for update the <i>st_ctime</i> and <i>st_mtime</i> fields of the file. The
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<i>fopen</i>() function shall allocate a file descriptor as <a href="../functions/open.html"><i>open</i>()</a> does. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>After a successful call to the <i>fopen</i>() function, the orientation of the stream shall be cleared, <sup>[<a href=
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"javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> the encoding
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rule shall be cleared, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> and the associated <b>mbstate_t</b> object
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shall be set to describe an initial conversion state.</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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largest value that can be represented correctly in an object of type <b>off_t</b> shall be established as the offset maximum in the
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open file description. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_176_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>fopen</i>() shall return a pointer to the object controlling the stream. Otherwise, a null
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pointer shall be returned, <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> and <i>errno</i> shall be set to indicate the error. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_176_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>fopen</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EACCES]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Search permission is denied on a component of the path prefix, or the file exists and the permissions specified by <i>mode</i> are
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denied, or the file does not exist and write permission is denied for the parent directory of the file to be created. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EINTR]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> A
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signal was caught during <i>fopen</i>(). <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EISDIR]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The named file is a directory and <i>mode</i> requires write access. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></dd>
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<dt>[ELOOP]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> A
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loop exists in symbolic links encountered during resolution of the <i>path</i> argument. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></dd>
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<dt>[EMFILE]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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{OPEN_MAX} file descriptors are currently open in the calling process. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></dd>
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<dt>[ENAMETOOLONG]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
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"0"><br>
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The length of the <i>filename</i> argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ENFILE]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The maximum allowable number of files is currently open in the system. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></dd>
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<dt>[ENOENT]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> A
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component of <i>filename</i> does not name an existing file or <i>filename</i> is an empty string. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></dd>
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<dt>[ENOSPC]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The directory or file system that would contain the new file cannot be expanded, the file does not exist, and the file was to be
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created. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ENOTDIR]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> A
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component of the path prefix is not a directory. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ENXIO]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The named file is a character special or block special file, and the device associated with this special file does not exist. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EOVERFLOW]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The named file is a regular file and the size of the file cannot be represented correctly in an object of type <b>off_t</b>. <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EROFS]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The named file resides on a read-only file system and <i>mode</i> requires write access. <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></dd>
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</dl>
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<p>The <i>fopen</i>() function may fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The value of the <i>mode</i> argument is not valid. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ELOOP]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the <i>path</i> argument. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EMFILE]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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{FOPEN_MAX} streams are currently open in the calling process. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EMFILE]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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{STREAM_MAX} streams are currently open in the calling process. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></dd>
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<dt>[ENAMETOOLONG]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
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"0"><br>
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Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ENOMEM]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Insufficient storage space is available. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[ETXTBSY]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The file is a pure procedure (shared text) file that is being executed and <i>mode</i> requires write access. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_176_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_176_06_01"></a>Opening a File</h5>
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<p>The following example tries to open the file named <b>file</b> for reading. The <i>fopen</i>() function returns a file pointer
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that is used in subsequent <a href="../functions/fgets.html"><i>fgets</i>()</a> and <a href=
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"../functions/fclose.html"><i>fclose</i>()</a> calls. If the program cannot open the file, it just ignores it.</p>
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<pre>
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<tt>#include <stdio.h>
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...
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FILE *fp;
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...
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void rgrep(const char *file)
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{
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...
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if ((fp = fopen(file, "r")) == NULL)
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return;
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...
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_176_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_176_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_176_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_176_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="fclose.html"><i>fclose</i>()</a> , <a href="fdopen.html"><i>fdopen</i>()</a> , <a href=
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"freopen.html"><i>freopen</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/stdio.h.html"><i><stdio.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_176_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_176_12"></a>Issue 5</h4>
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<blockquote>
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<p>Large File Summit extensions are added.</p>
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</blockquote>
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<h4><a name="tag_03_176_13"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
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<ul>
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<li>
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<p>In the DESCRIPTION, text is added to indicate setting of the offset maximum in the open file description. This change is to
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support large files.</p>
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</li>
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<li>
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<p>In the ERRORS section, the [EOVERFLOW] condition is added. This change is to support large files.</p>
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</li>
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<li>
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<p>The [ELOOP] mandatory error condition is added.</p>
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</li>
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<li>
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<p>The [EINVAL], [EMFILE], [ENAMETOOLONG], [ENOMEM], and [ETXTBSY] optional error conditions are added.</p>
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</li>
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</ul>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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<p>The following changes are made for alignment with the ISO/IEC 9899:1999 standard:</p>
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<ul>
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<li>
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<p>The prototype for <i>fopen</i>() is updated.</p>
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</li>
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<li>
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<p>The DESCRIPTION is updated to note that if the argument <i>mode</i> points to a string other than those listed, then the
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behavior is undefined.</p>
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</li>
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</ul>
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<p>The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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