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136 lines
5.6 KiB
HTML
136 lines
5.6 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>setvbuf (The Red Hat newlib C Library)</title>
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<meta name="description" content="setvbuf (The Red Hat newlib C Library)">
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<meta name="keywords" content="setvbuf (The Red Hat newlib C Library)">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Stdio.html#Stdio" rel="up" title="Stdio">
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<link href="siprintf.html#siprintf" rel="next" title="siprintf">
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</head>
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<body lang="en">
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<a name="setvbuf"></a>
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<div class="header">
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<p>
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Next: <a href="siprintf.html#siprintf" accesskey="n" rel="next">siprintf</a>, Previous: <a href="setlinebuf.html#setlinebuf" accesskey="p" rel="prev">setlinebuf</a>, Up: <a href="Stdio.html#Stdio" accesskey="u" rel="up">Stdio</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="setvbuf_002d_002d_002dspecify-file-or-stream-buffering"></a>
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<h3 class="section">4.58 <code>setvbuf</code>—specify file or stream buffering</h3>
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<a name="index-setvbuf"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <stdio.h>
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int setvbuf(FILE *<var>fp</var>, char *<var>buf</var>,
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int <var>mode</var>, size_t <var>size</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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Use <code>setvbuf</code> to specify what kind of buffering you want for the
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file or stream identified by <var>fp</var>, by using one of the following
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values (from <code>stdio.h</code>) as the <var>mode</var> argument:
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</p>
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<dl compact="compact">
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<dt><code>_IONBF</code></dt>
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<dd><p>Do not use a buffer: send output directly to the host system for the
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file or stream identified by <var>fp</var>.
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</p>
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</dd>
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<dt><code>_IOFBF</code></dt>
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<dd><p>Use full output buffering: output will be passed on to the host system
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only when the buffer is full, or when an input operation intervenes.
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</p>
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</dd>
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<dt><code>_IOLBF</code></dt>
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<dd><p>Use line buffering: pass on output to the host system at every
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newline, as well as when the buffer is full, or when an input
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operation intervenes.
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</p></dd>
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</dl>
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<p>Use the <var>size</var> argument to specify how large a buffer you wish. You
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can supply the buffer itself, if you wish, by passing a pointer to a
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suitable area of memory as <var>buf</var>. Otherwise, you may pass <code>NULL</code>
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as the <var>buf</var> argument, and <code>setvbuf</code> will allocate the buffer.
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</p>
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<br>
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<p><strong>Warnings</strong><br>
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You may only use <code>setvbuf</code> before performing any file operation other
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than opening the file.
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</p>
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<p>If you supply a non-null <var>buf</var>, you must ensure that the associated
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storage continues to be available until you close the stream
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identified by <var>fp</var>.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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A <code>0</code> result indicates success, <code>EOF</code> failure (invalid <var>mode</var> or
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<var>size</var> can cause failure).
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</p>
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<br>
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<p><strong>Portability</strong><br>
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Both ANSI C and the System V Interface Definition (Issue 2) require
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<code>setvbuf</code>. However, they differ on the meaning of a <code>NULL</code> buffer
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pointer: the SVID issue 2 specification says that a <code>NULL</code> buffer
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pointer requests unbuffered output. For maximum portability, avoid
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<code>NULL</code> buffer pointers.
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</p>
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<p>Both specifications describe the result on failure only as a
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nonzero value.
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</p>
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<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
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<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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</p>
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<br>
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<hr>
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<div class="header">
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<p>
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Next: <a href="siprintf.html#siprintf" accesskey="n" rel="next">siprintf</a>, Previous: <a href="setlinebuf.html#setlinebuf" accesskey="p" rel="prev">setlinebuf</a>, Up: <a href="Stdio.html#Stdio" accesskey="u" rel="up">Stdio</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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