225 lines
8.9 KiB
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225 lines
8.9 KiB
HTML
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<title>ftruncate</title>
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<basefont size="3"> <a name="ftruncate"></a> <a name="tag_03_199"></a><!-- ftruncate -->
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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_199_01"></a>NAME</h4>
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<blockquote>ftruncate - truncate a file to a specified length</blockquote>
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<h4><a name="tag_03_199_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
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<br>
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int ftruncate(int</tt> <i>fildes</i><tt>, off_t</tt> <i>length</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_199_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>If <i>fildes</i> is not a valid file descriptor open for writing, the <i>ftruncate</i>() function shall fail.</p>
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<p>If <i>fildes</i> refers to a regular file, the <i>ftruncate</i>() function shall cause the size of the file to be truncated to
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<i>length</i>. If the size of the file previously exceeded <i>length</i>, the extra data shall no longer be available to reads on
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the file. If the file previously was smaller than this size, <i>ftruncate</i>() shall either increase the size of the file or fail.
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<sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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XSI-conformant systems shall increase the size of the file. <img src="../images/opt-end.gif" alt="[Option End]" border="0">
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If the file size is increased, the extended area shall appear as if it were zero-filled. The value of the seek pointer shall not be
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modified by a call to <i>ftruncate</i>().</p>
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<p>Upon successful completion, if <i>fildes</i> refers to a regular file, the <i>ftruncate</i>() function shall mark for update the
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<i>st_ctime</i> and <i>st_mtime</i> fields of the file and the S_ISUID and S_ISGID bits of the file mode may be cleared. If the
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<i>ftruncate</i>() function is unsuccessful, the file is unaffected.</p>
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<p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If the request would cause the file size to exceed the soft file size limit for the process, the request shall fail and the
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implementation shall generate the SIGXFSZ signal for the thread. <img src="../images/opt-end.gif" alt="[Option End]" border=
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"0"></p>
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<p>If <i>fildes</i> refers to a directory, <i>ftruncate</i>() shall fail.</p>
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<p>If <i>fildes</i> refers to any other file type, except a shared memory object, the result is unspecified.</p>
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<p><sup>[<a href="javascript:open_code('SHM')">SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If <i>fildes</i> refers to a shared memory object, <i>ftruncate</i>() shall set the size of the shared memory object to
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<i>length</i>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('MF')">MF|SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If the effect of <i>ftruncate</i>() is to decrease the size of a shared memory object or memory mapped file and whole pages beyond
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the new end were previously mapped, then the whole pages beyond the new end shall be discarded. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('MPR')">MPR</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If the Memory Protection option is supported, references to discarded pages shall result in the generation of a SIGBUS signal;
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otherwise, the result of such references is undefined. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p><sup>[<a href="javascript:open_code('MF')">MF|SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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If the effect of <i>ftruncate</i>() is to increase the size of a shared memory object, it is unspecified whether the contents of
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any mapped pages between the old end-of-file and the new are flushed to the underlying object. <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_199_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>ftruncate</i>() shall return 0; otherwise, -1 shall be returned and <i>errno</i> set to indicate
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the error.</p>
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</blockquote>
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<h4><a name="tag_03_199_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>ftruncate</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINTR]</dt>
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<dd>A signal was caught during execution.</dd>
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<dt>[EINVAL]</dt>
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<dd>The <i>length</i> argument was less than 0.</dd>
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<dt>[EFBIG] or [EINVAL]</dt>
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<dd><br>
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The <i>length</i> argument was greater than the maximum file size.</dd>
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<dt>[EFBIG]</dt>
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<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The file is a regular file and <i>length</i> is greater than the offset maximum established in the open file description associated
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with <i>fildes</i>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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<dt>[EIO]</dt>
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<dd>An I/O error occurred while reading from or writing to a file system.</dd>
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<dt>[EBADF] or [EINVAL]</dt>
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<dd><br>
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The <i>fildes</i> argument is not a file descriptor open for writing.</dd>
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<dt>[EINVAL]</dt>
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<dd>The <i>fildes</i> argument references a file that was opened without write permission.</dd>
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<dt>[EROFS]</dt>
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<dd>The named file resides on a read-only file system.</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_199_06"></a>EXAMPLES</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_199_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_199_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>ftruncate</i>() function is part of IEEE Std 1003.1-2001 as it was deemed to be more useful than <a href=
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"../functions/truncate.html"><i>truncate</i>()</a>. The <a href="../functions/truncate.html"><i>truncate</i>()</a> function is
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provided as an XSI extension.</p>
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</blockquote>
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<h4><a name="tag_03_199_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_199_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="open.html"><i>open</i>()</a> , <a href="truncate.html"><i>truncate</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_199_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_199_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE and aligned with <i>ftruncate</i>() in the POSIX Realtime Extension. Specifically, the
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DESCRIPTION is extensively reworded and [EROFS] is added to the list of mandatory errors that can be returned by
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<i>ftruncate</i>().</p>
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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_199_13"></a>Issue 6</h4>
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<blockquote>
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<p>The <a href="../functions/truncate.html"><i>truncate</i>()</a> function has been split out into a separate reference page.</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>The DESCRIPTION is changed to indicate that if the file size is changed, and if the file is a regular file, the S_ISUID and
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S_ISGID bits in the file mode may be cleared.</p>
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</li>
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</ul>
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<p>The following changes were made to align with the IEEE P1003.1a draft standard:</p>
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<ul>
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<li>
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<p>The DESCRIPTION text is updated.</p>
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</li>
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</ul>
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<p>XSI-conformant systems are required to increase the size of the file if the file was previously smaller than the size
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requested.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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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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