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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>truncate</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="truncate"></a> <a name="tag_03_790"></a><!-- truncate --> <!--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_790_01"></a>NAME</h4><blockquote>truncate - truncate a file to a specified length</blockquote><h4><a name="tag_03_790_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br><br> int truncate(const char *</tt><i>path</i><tt>, off_t</tt> <i>length</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]"border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_790_03"></a>DESCRIPTION</h4><blockquote><p>The <i>truncate</i>() function shall cause the regular file named by <i>path</i> to have a size which shall be equal to<i>length</i> bytes.</p><p>If the file previously was larger than <i>length</i>, the extra data is discarded. If the file was previously shorter than<i>length</i>, its size is increased, and the extended area appears as if it were zero-filled.</p><p>The application shall ensure that the process has write permission for the file.</p><p>If the request would cause the file size to exceed the soft file size limit for the process, the request shall fail and theimplementation shall generate the SIGXFSZ signal for the process.</p><p>This function shall not modify the file offset for any open file descriptions associated with the file. Upon successfulcompletion, if the file size is changed, this function shall mark for update the <i>st_ctime</i> and <i>st_mtime</i> fields of thefile, and the S_ISUID and S_ISGID bits of the file mode may be cleared.</p></blockquote><h4><a name="tag_03_790_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, <i>truncate</i>() shall return 0. Otherwise, -1 shall be returned, and <i>errno</i> set to indicatethe error.</p></blockquote><h4><a name="tag_03_790_05"></a>ERRORS</h4><blockquote><p>The <i>truncate</i>() function shall fail if:</p><dl compact><dt>[EINTR]</dt><dd>A signal was caught during execution.</dd><dt>[EINVAL]</dt><dd>The <i>length</i> argument was less than 0.</dd><dt>[EFBIG] or [EINVAL]</dt><dd>The <i>length</i> argument was greater than the maximum file size.</dd><dt>[EIO]</dt><dd>An I/O error occurred while reading from or writing to a file system.</dd><dt>[EACCES]</dt><dd>A component of the path prefix denies search permission, or write permission is denied on the file.</dd><dt>[EISDIR]</dt><dd>The named file is a directory.</dd><dt>[ELOOP]</dt><dd>A loop exists in symbolic links encountered during resolution of the <i>path</i> argument.</dd><dt>[ENAMETOOLONG]</dt><dd>The length of the <i>path</i> argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.</dd><dt>[ENOENT]</dt><dd>A component of <i>path</i> does not name an existing file or <i>path</i> is an empty string.</dd><dt>[ENOTDIR]</dt><dd>A component of the path prefix of <i>path</i> is not a directory.</dd><dt>[EROFS]</dt><dd>The named file resides on a read-only file system.</dd></dl><p>The <i>truncate</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>path</i> argument.</dd><dt>[ENAMETOOLONG]</dt><dd>Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_790_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_790_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_790_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_790_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_790_10"></a>SEE ALSO</h4><blockquote><p><a href="open.html"><i>open</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p></blockquote><h4><a name="tag_03_790_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_790_12"></a>Issue 5</h4><blockquote><p>Moved from X/OPEN UNIX extension to BASE.</p><p>Large File Summit extensions are added.</p></blockquote><h4><a name="tag_03_790_13"></a>Issue 6</h4><blockquote><p>This reference page is split out from the <a href="../functions/ftruncate.html"><i>ftruncate</i>()</a> reference page.</p><p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p><p>The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.</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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