1<html lang="en"> 2<head> 3<title>freopen - 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="fread.html#fread" title="fread"> 10<link rel="next" href="fseek.html#fseek" title="fseek"> 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="freopen"></a> 29<p> 30Next: <a rel="next" accesskey="n" href="fseek.html#fseek">fseek</a>, 31Previous: <a rel="previous" accesskey="p" href="fread.html#fread">fread</a>, 32Up: <a rel="up" accesskey="u" href="Stdio.html#Stdio">Stdio</a> 33<hr> 34</div> 35 36<h3 class="section">4.25 <code>freopen</code>—open a file using an existing file descriptor</h3> 37 38<p><a name="index-freopen-196"></a><a name="index-g_t_005ffreopen_005fr-197"></a><strong>Synopsis</strong> 39<pre class="example"> #include <stdio.h> 40 FILE *freopen(const char *<var>file</var>, const char *<var>mode</var>, 41 FILE *<var>fp</var>); 42 FILE *_freopen_r(struct _reent *<var>ptr</var>, const char *<var>file</var>, 43 const char *<var>mode</var>, FILE *<var>fp</var>); 44 45</pre> 46 <p><strong>Description</strong><br> 47Use this variant of <code>fopen</code> if you wish to specify a particular file 48descriptor <var>fp</var> (notably <code>stdin</code>, <code>stdout</code>, or <code>stderr</code>) for 49the file. 50 51 <p>If <var>fp</var> was associated with another file or stream, <code>freopen</code> 52closes that other file or stream (but ignores any errors while closing 53it). 54 55 <p><var>file</var> and <var>mode</var> are used just as in <code>fopen</code>. 56 57 <p>If <var>file</var> is <code>NULL</code>, the underlying stream is modified rather than 58closed. The file cannot be given a more permissive access mode (for 59example, a <var>mode</var> of "w" will fail on a read-only file descriptor), 60but can change status such as append or binary mode. If modification 61is not possible, failure occurs. 62 63 <p><br> 64<strong>Returns</strong><br> 65If successful, the result is the same as the argument <var>fp</var>. If the 66file cannot be opened as specified, the result is <code>NULL</code>. 67 68 <p><br> 69<strong>Portability</strong><br> 70ANSI C requires <code>freopen</code>. 71 72 <p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>, 73<code>lseek</code>, <code>open</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>. 74 75 <p><br> 76 77 </body></html> 78 79