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<div class="subsection" id="File-Positioning">
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<p>
Previous: <a href="EOF-and-Errors.html" accesskey="p" rel="prev">End of File and Errors</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html" accesskey="u" rel="up">C-Style I/O Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
<span id="File-Positioning-1"></span><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.
</p>
<span id="XREFftell"></span><dl class="def">
<dt id="index-ftell"><span class="category">: </span><span><em><var>pos</var> =</em> <strong>ftell</strong> <em>(<var>fid</var>)</em><a href='#index-ftell' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Return the position of the file pointer as the number of characters from the
beginning of the file specified by file descriptor <var>fid</var>.
</p>
<p><strong>See also:</strong> <a href="#XREFfseek">fseek</a>, <a href="#XREFfrewind">frewind</a>, <a href="EOF-and-Errors.html#XREFfeof">feof</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<span id="XREFfseek"></span><dl class="def">
<dt id="index-fseek"><span class="category">: </span><span><em></em> <strong>fseek</strong> <em>(<var>fid</var>, <var>offset</var>)</em><a href='#index-fseek' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-fseek-1"><span class="category">: </span><span><em></em> <strong>fseek</strong> <em>(<var>fid</var>, <var>offset</var>, <var>origin</var>)</em><a href='#index-fseek-1' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-fseek-2"><span class="category">: </span><span><em><var>status</var> =</em> <strong>fseek</strong> <em>(…)</em><a href='#index-fseek-2' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Set the file pointer to the location <var>offset</var> within the file <var>fid</var>.
</p>
<p>The pointer is positioned <var>offset</var> characters from the <var>origin</var>, which
may be one of the predefined variables <code><span class="nolinebreak">SEEK_SET</span></code><!-- /@w --> (beginning),
<code><span class="nolinebreak">SEEK_CUR</span></code><!-- /@w --> (current position), or <code><span class="nolinebreak">SEEK_END</span></code><!-- /@w --> (end of file)
or strings <code>"bof"</code>, <code>"cof"</code>, or
<code>"eof"</code>. If <var>origin</var> is omitted, <code><span class="nolinebreak">SEEK_SET</span></code><!-- /@w --> is
assumed. <var>offset</var> may be positive, negative, or zero but not all
combinations of <var>origin</var> and <var>offset</var> can be realized.
</p>
<p><code>fseek</code> returns 0 on success and -1 on error.
</p>
<p><strong>See also:</strong> <a href="Line_002dOriented-Input.html#XREFfskipl">fskipl</a>, <a href="#XREFfrewind">frewind</a>, <a href="#XREFftell">ftell</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>, <a href="#XREFSEEK_005fSET">SEEK_SET</a>, <a href="#XREFSEEK_005fCUR">SEEK_CUR</a>, <a href="#XREFSEEK_005fEND">SEEK_END</a>.
</p></dd></dl>
<span id="XREFSEEK_005fSET"></span><dl class="def">
<dt id="index-SEEK_005fSET"><span class="category">: </span><span><em></em> <strong>SEEK_SET</strong> <em>()</em><a href='#index-SEEK_005fSET' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Return the numerical value to pass to <code>fseek</code> to position the file pointer
relative to the beginning of the file.
</p>
<p><strong>See also:</strong> <a href="#XREFSEEK_005fCUR">SEEK_CUR</a>, <a href="#XREFSEEK_005fEND">SEEK_END</a>, <a href="#XREFfseek">fseek</a>.
</p></dd></dl>
<span id="XREFSEEK_005fCUR"></span><dl class="def">
<dt id="index-SEEK_005fCUR"><span class="category">: </span><span><em></em> <strong>SEEK_CUR</strong> <em>()</em><a href='#index-SEEK_005fCUR' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Return the numerical value to pass to <code>fseek</code> to position the file pointer
relative to the current position.
</p>
<p><strong>See also:</strong> <a href="#XREFSEEK_005fSET">SEEK_SET</a>, <a href="#XREFSEEK_005fEND">SEEK_END</a>, <a href="#XREFfseek">fseek</a>.
</p></dd></dl>
<span id="XREFSEEK_005fEND"></span><dl class="def">
<dt id="index-SEEK_005fEND"><span class="category">: </span><span><em></em> <strong>SEEK_END</strong> <em>()</em><a href='#index-SEEK_005fEND' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Return the numerical value to pass to <code>fseek</code> to position the file pointer
relative to the end of the file.
</p>
<p><strong>See also:</strong> <a href="#XREFSEEK_005fSET">SEEK_SET</a>, <a href="#XREFSEEK_005fCUR">SEEK_CUR</a>, <a href="#XREFfseek">fseek</a>.
</p></dd></dl>
<span id="XREFfrewind"></span><dl class="def">
<dt id="index-frewind"><span class="category">: </span><span><em></em> <strong>frewind</strong> <em>(<var>fid</var>)</em><a href='#index-frewind' class='copiable-anchor'> ¶</a></span></dt>
<dt id="index-frewind-1"><span class="category">: </span><span><em><var>status</var> =</em> <strong>frewind</strong> <em>(<var>fid</var>)</em><a href='#index-frewind-1' class='copiable-anchor'> ¶</a></span></dt>
<dd><p>Move the file pointer to the beginning of the file specified by file
descriptor <var>fid</var>.
</p>
<p><code>frewind</code> returns 0 for success, and -1 if an error is encountered. It
is equivalent to <code>fseek (<var>fid</var>, 0, SEEK_SET)</code>.
</p>
<p><strong>See also:</strong> <a href="#XREFfseek">fseek</a>, <a href="#XREFftell">ftell</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<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.
</p>
<div class="example">
<pre class="example">marker = ftell (myfile);
frewind (myfile);
fourch = fgets (myfile, 4);
fseek (myfile, marker, SEEK_SET);
</pre></div>
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