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109 lines
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109 lines
4.5 KiB
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<a name="setbuf"></a>
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<div class="header">
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<p>
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Next: <a href="setbuffer.html#setbuffer" accesskey="n" rel="next">setbuffer</a>, Previous: <a href="rewind.html#rewind" accesskey="p" rel="prev">rewind</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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<hr>
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<a name="setbuf_002d_002d_002dspecify-full-buffering-for-a-file-or-stream"></a>
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<h3 class="section">4.55 <code>setbuf</code>—specify full buffering for a file or stream</h3>
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<a name="index-setbuf"></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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void setbuf(FILE *<var>fp</var>, char *<var>buf</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>setbuf</code> specifies that output to the file or stream identified by <var>fp</var>
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should be fully buffered. All output for this file will go to a
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buffer (of size <code>BUFSIZ</code>, specified in ‘<code>stdio.h</code>’). Output will
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be passed on to the host system only when the buffer is full, or when
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an input operation intervenes.
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</p>
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<p>You may, if you wish, supply your own buffer by passing a pointer to
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it as the argument <var>buf</var>. It must have size <code>BUFSIZ</code>. You can
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also use <code>NULL</code> as the value of <var>buf</var>, to signal that the
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<code>setbuf</code> function is to 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>setbuf</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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<code>setbuf</code> does not return a result.
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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>setbuf</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>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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