1<html lang="en"> 2<head> 3<title>setbuf - 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="rewind.html#rewind" title="rewind"> 10<link rel="next" href="setbuffer.html#setbuffer" title="setbuffer"> 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="setbuf"></a> 29<p> 30Next: <a rel="next" accesskey="n" href="setbuffer.html#setbuffer">setbuffer</a>, 31Previous: <a rel="previous" accesskey="p" href="rewind.html#rewind">rewind</a>, 32Up: <a rel="up" accesskey="u" href="Stdio.html#Stdio">Stdio</a> 33<hr> 34</div> 35 36<h3 class="section">4.54 <code>setbuf</code>—specify full buffering for a file or stream</h3> 37 38<p><a name="index-setbuf-263"></a><strong>Synopsis</strong> 39<pre class="example"> #include <stdio.h> 40 void setbuf(FILE *<var>fp</var>, char *<var>buf</var>); 41 42</pre> 43 <p><strong>Description</strong><br> 44<code>setbuf</code> specifies that output to the file or stream identified by <var>fp</var> 45should be fully buffered. All output for this file will go to a 46buffer (of size <code>BUFSIZ</code>, specified in `<code>stdio.h</code>'). Output will 47be passed on to the host system only when the buffer is full, or when 48an input operation intervenes. 49 50 <p>You may, if you wish, supply your own buffer by passing a pointer to 51it as the argument <var>buf</var>. It must have size <code>BUFSIZ</code>. You can 52also use <code>NULL</code> as the value of <var>buf</var>, to signal that the 53<code>setbuf</code> function is to allocate the buffer. 54 55 <p><br> 56<strong>Warnings</strong><br> 57You may only use <code>setbuf</code> before performing any file operation other 58than opening the file. 59 60 <p>If you supply a non-null <var>buf</var>, you must ensure that the associated 61storage continues to be available until you close the stream 62identified by <var>fp</var>. 63 64 <p><br> 65<strong>Returns</strong><br> 66<code>setbuf</code> does not return a result. 67 68 <p><br> 69<strong>Portability</strong><br> 70Both ANSI C and the System V Interface Definition (Issue 2) require 71<code>setbuf</code>. However, they differ on the meaning of a <code>NULL</code> buffer 72pointer: the SVID issue 2 specification says that a <code>NULL</code> buffer 73pointer requests unbuffered output. For maximum portability, avoid 74<code>NULL</code> buffer pointers. 75 76 <p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>, 77<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>. 78 79 <p><br> 80 81 </body></html> 82 83