<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>File Positioning (GNU Octave (version 5.1.0))</title>
<meta name="description" content="File Positioning (GNU Octave (version 5.1.0))">
<meta name="keywords" content="File Positioning (GNU Octave (version 5.1.0))">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" rel="up" title="C-Style I/O Functions">
<link href="Plotting.html#Plotting" rel="next" title="Plotting">
<link href="EOF-and-Errors.html#EOF-and-Errors" rel="prev" title="EOF and Errors">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>
<link rel="stylesheet" type="text/css" href="octave.css">
</head>
<body lang="en">
<a name="File-Positioning"></a>
<div class="header">
<p>
Previous: <a href="EOF-and-Errors.html#EOF-and-Errors" accesskey="p" rel="prev">EOF and Errors</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" 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#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="File-Positioning-1"></a>
<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>
<a name="XREFftell"></a><dl>
<dt><a name="index-ftell"></a><em><var>pos</var> =</em> <strong>ftell</strong> <em>(<var>fid</var>)</em></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>
<a name="XREFfseek"></a><dl>
<dt><a name="index-fseek"></a><em></em> <strong>fseek</strong> <em>(<var>fid</var>, <var>offset</var>)</em></dt>
<dt><a name="index-fseek-1"></a><em></em> <strong>fseek</strong> <em>(<var>fid</var>, <var>offset</var>, <var>origin</var>)</em></dt>
<dt><a name="index-fseek-2"></a><em><var>status</var> =</em> <strong>fseek</strong> <em>(…)</em></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>
<a name="XREFSEEK_005fSET"></a><dl>
<dt><a name="index-SEEK_005fSET"></a><em></em> <strong>SEEK_SET</strong> <em>()</em></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>
<a name="XREFSEEK_005fCUR"></a><dl>
<dt><a name="index-SEEK_005fCUR"></a><em></em> <strong>SEEK_CUR</strong> <em>()</em></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>
<a name="XREFSEEK_005fEND"></a><dl>
<dt><a name="index-SEEK_005fEND"></a><em></em> <strong>SEEK_END</strong> <em>()</em></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>
<a name="XREFfrewind"></a><dl>
<dt><a name="index-frewind"></a><em></em> <strong>frewind</strong> <em>(<var>fid</var>)</em></dt>
<dt><a name="index-frewind-1"></a><em><var>status</var> =</em> <strong>frewind</strong> <em>(<var>fid</var>)</em></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>
<hr>
<div class="header">
<p>
Previous: <a href="EOF-and-Errors.html#EOF-and-Errors" accesskey="p" rel="prev">EOF and Errors</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html#C_002dStyle-I_002fO-Functions" 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#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
</body>
</html>
