1<html lang="en"> 2<head> 3<title>setvbuf - 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="setlinebuf.html#setlinebuf" title="setlinebuf"> 10<link rel="next" href="siprintf.html#siprintf" title="siprintf"> 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="setvbuf"></a> 29<p> 30Next: <a rel="next" accesskey="n" href="siprintf.html#siprintf">siprintf</a>, 31Previous: <a rel="previous" accesskey="p" href="setlinebuf.html#setlinebuf">setlinebuf</a>, 32Up: <a rel="up" accesskey="u" href="Stdio.html#Stdio">Stdio</a> 33<hr> 34</div> 35 36<h3 class="section">4.57 <code>setvbuf</code>—specify file or stream buffering</h3> 37 38<p><a name="index-setvbuf-266"></a><strong>Synopsis</strong> 39<pre class="example"> #include <stdio.h> 40 int setvbuf(FILE *<var>fp</var>, char *<var>buf</var>, 41 int <var>mode</var>, size_t <var>size</var>); 42 43</pre> 44 <p><strong>Description</strong><br> 45Use <code>setvbuf</code> to specify what kind of buffering you want for the 46file or stream identified by <var>fp</var>, by using one of the following 47values (from <code>stdio.h</code>) as the <var>mode</var> argument: 48 49 <dl> 50<dt><code>_IONBF</code><dd>Do not use a buffer: send output directly to the host system for the 51file or stream identified by <var>fp</var>. 52 53 <br><dt><code>_IOFBF</code><dd>Use full output buffering: output will be passed on to the host system 54only when the buffer is full, or when an input operation intervenes. 55 56 <br><dt><code>_IOLBF</code><dd>Use line buffering: pass on output to the host system at every 57newline, as well as when the buffer is full, or when an input 58operation intervenes. 59</dl> 60 61 <p>Use the <var>size</var> argument to specify how large a buffer you wish. You 62can supply the buffer itself, if you wish, by passing a pointer to a 63suitable area of memory as <var>buf</var>. Otherwise, you may pass <code>NULL</code> 64as the <var>buf</var> argument, and <code>setvbuf</code> will allocate the buffer. 65 66 <p><br> 67<strong>Warnings</strong><br> 68You may only use <code>setvbuf</code> before performing any file operation other 69than opening the file. 70 71 <p>If you supply a non-null <var>buf</var>, you must ensure that the associated 72storage continues to be available until you close the stream 73identified by <var>fp</var>. 74 75 <p><br> 76<strong>Returns</strong><br> 77A <code>0</code> result indicates success, <code>EOF</code> failure (invalid <var>mode</var> or 78<var>size</var> can cause failure). 79 80 <p><br> 81<strong>Portability</strong><br> 82Both ANSI C and the System V Interface Definition (Issue 2) require 83<code>setvbuf</code>. However, they differ on the meaning of a <code>NULL</code> buffer 84pointer: the SVID issue 2 specification says that a <code>NULL</code> buffer 85pointer requests unbuffered output. For maximum portability, avoid 86<code>NULL</code> buffer pointers. 87 88 <p>Both specifications describe the result on failure only as a 89nonzero value. 90 91 <p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>, 92<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>. 93 94 <p><br> 95 96 </body></html> 97 98