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<title>File Positioning - Untitled</title>
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<p>
<a name="File-Positioning"></a>
Previous: <a rel="previous" accesskey="p" href="EOF-and-Errors.html#EOF-and-Errors">EOF and Errors</a>,
Up: <a rel="up" accesskey="u" href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions">C-Style I/O Functions</a>
<hr>
</div>
<h4 class="subsection">14.2.19 File Positioning</h4>
<p>Three functions are available for setting and determining the position of
the file pointer for a given file.
<!-- file-io.cc -->
<p><a name="doc_002dftell"></a>
<div class="defun">
— Built-in Function: <b>ftell</b> (<var>fid</var>)<var><a name="index-ftell-809"></a></var><br>
<blockquote><p>Return the position of the file pointer as the number of characters
from the beginning of the file <var>fid</var>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dfseek.html#doc_002dfseek">fseek</a>, <a href="doc_002dfopen.html#doc_002dfopen">fopen</a>, <a href="doc_002dfclose.html#doc_002dfclose">fclose</a>.
</p></blockquote></div>
<!-- file-io.cc -->
<p><a name="doc_002dfseek"></a>
<div class="defun">
— Built-in Function: <b>fseek</b> (<var>fid, offset, origin</var>)<var><a name="index-fseek-810"></a></var><br>
<blockquote><p>Set the file pointer to any location within the file <var>fid</var>.
<p>The pointer is positioned <var>offset</var> characters from the <var>origin</var>,
which may be one of the predefined variables <code>SEEK_CUR</code><!-- /@w --> (current
position), <code>SEEK_SET</code><!-- /@w --> (beginning), or <code>SEEK_END</code><!-- /@w --> (end of
file) or strings "cof", "bof" or "eof". If <var>origin</var> is omitted,
<code>SEEK_SET</code><!-- /@w --> is assumed. The offset must be zero, or a value returned
by <code>ftell</code> (in which case <var>origin</var> must be <code>SEEK_SET</code><!-- /@w -->).
<p>Return 0 on success and -1 on error.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dftell.html#doc_002dftell">ftell</a>, <a href="doc_002dfopen.html#doc_002dfopen">fopen</a>, <a href="doc_002dfclose.html#doc_002dfclose">fclose</a>.
</p></blockquote></div>
<!-- file-io.cc -->
<p><a name="doc_002dSEEK_005fSET"></a>
<div class="defun">
— Built-in Function: <b>SEEK_SET</b> ()<var><a name="index-SEEK_005fSET-811"></a></var><br>
— Built-in Function: <b>SEEK_CUR</b> ()<var><a name="index-SEEK_005fCUR-812"></a></var><br>
— Built-in Function: <b>SEEK_END</b> ()<var><a name="index-SEEK_005fEND-813"></a></var><br>
<blockquote><p>Return the value required to request that <code>fseek</code> perform
one of the following actions:
<dl>
<dt><code>SEEK_SET</code><dd>Position file relative to the beginning.
<br><dt><code>SEEK_CUR</code><dd>Position file relative to the current position.
<br><dt><code>SEEK_END</code><dd>Position file relative to the end.
</dl>
</p></blockquote></div>
<!-- file-io.cc -->
<p><a name="doc_002dfrewind"></a>
<div class="defun">
— Built-in Function: <b>frewind</b> (<var>fid</var>)<var><a name="index-frewind-814"></a></var><br>
<blockquote><p>Move the file pointer to the beginning of the file <var>fid</var>, returning
0 for success, and -1 if an error was encountered. It is equivalent to
<code>fseek (</code><var>fid</var><code>, 0, SEEK_SET)</code>.
</p></blockquote></div>
<p>The following example stores the current file position in the variable
<code>marker</code>, moves the pointer to the beginning of the file, reads
four characters, and then returns to the original position.
<pre class="example"> marker = ftell (myfile);
frewind (myfile);
fourch = fgets (myfile, 4);
fseek (myfile, marker, SEEK_SET);
</pre>
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