1<html lang="en"> 2<head> 3<title>ftell - Untitled</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Untitled"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Stdio.html#Stdio" title="Stdio"> 9<link rel="prev" href="fsetpos.html#fsetpos" title="fsetpos"> 10<link rel="next" href="funopen.html#funopen" title="funopen"> 11<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 12<meta http-equiv="Content-Style-Type" content="text/css"> 13<style type="text/css"><!-- 14 pre.display { font-family:inherit } 15 pre.format { font-family:inherit } 16 pre.smalldisplay { font-family:inherit; font-size:smaller } 17 pre.smallformat { font-family:inherit; font-size:smaller } 18 pre.smallexample { font-size:smaller } 19 pre.smalllisp { font-size:smaller } 20 span.sc { font-variant:small-caps } 21 span.roman { font-family:serif; font-weight:normal; } 22 span.sansserif { font-family:sans-serif; font-weight:normal; } 23--></style> 24<link rel="stylesheet" type="text/css" href="../cs.css"> 25</head> 26<body> 27<div class="node"> 28<a name="ftell"></a> 29<p> 30Next: <a rel="next" accesskey="n" href="funopen.html#funopen">funopen</a>, 31Previous: <a rel="previous" accesskey="p" href="fsetpos.html#fsetpos">fsetpos</a>, 32Up: <a rel="up" accesskey="u" href="Stdio.html#Stdio">Stdio</a> 33<hr> 34</div> 35 36<h3 class="section">4.28 <code>ftell</code>, <code>ftello</code>—return position in a stream or file</h3> 37 38<p><a name="index-ftell-204"></a><a name="index-ftello-205"></a><a name="index-g_t_005fftell_005fr-206"></a><a name="index-g_t_005fftello_005fr-207"></a><strong>Synopsis</strong> 39<pre class="example"> #include <stdio.h> 40 long ftell(FILE *<var>fp</var>); 41 off_t ftello(FILE *<var>fp</var>); 42 long _ftell_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>); 43 off_t _ftello_r(struct _reent *<var>ptr</var>, FILE *<var>fp</var>); 44 45</pre> 46 <p><strong>Description</strong><br> 47Objects of type <code>FILE</code> can have a “position” that records how much 48of the file your program has already read. Many of the <code>stdio</code> functions 49depend on this position, and many change it as a side effect. 50 51 <p>The result of <code>ftell</code>/<code>ftello</code> is the current position for a file 52identified by <var>fp</var>. If you record this result, you can later 53use it with <code>fseek</code>/<code>fseeko</code> to return the file to this 54position. The difference between <code>ftell</code> and <code>ftello</code> is that 55<code>ftell</code> returns <code>long</code> and <code>ftello</code> returns <code>off_t</code>. 56 57 <p>In the current implementation, <code>ftell</code>/<code>ftello</code> simply uses a character 58count to represent the file position; this is the same number that 59would be recorded by <code>fgetpos</code>. 60 61 <p><br> 62<strong>Returns</strong><br> 63<code>ftell</code>/<code>ftello</code> return the file position, if possible. If they cannot do 64this, they return <code>-1L</code>. Failure occurs on streams that do not support 65positioning; the global <code>errno</code> indicates this condition with the 66value <code>ESPIPE</code>. 67 68 <p><br> 69<strong>Portability</strong><br> 70<code>ftell</code> is required by the ANSI C standard, but the meaning of its 71result (when successful) is not specified beyond requiring that it be 72acceptable as an argument to <code>fseek</code>. In particular, other 73conforming C implementations may return a different result from 74<code>ftell</code> than what <code>fgetpos</code> records. 75 76 <p><code>ftello</code> is defined by the Single Unix specification. 77 78 <p>No supporting OS subroutines are required. 79 80 <p><br> 81 82 </body></html> 83 84