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<a name="setbuf_002d_002d_002dspecify-full-buffering-for-a-file-or-stream"></a>
<h3 class="section">4.55 <code>setbuf</code>&mdash;specify full buffering for a file or stream</h3>
<a name="index-setbuf"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdio.h&gt;
void setbuf(FILE *<var>fp</var>, char *<var>buf</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>setbuf</code> specifies that output to the file or stream identified by <var>fp</var>
should be fully buffered.  All output for this file will go to a
buffer (of size <code>BUFSIZ</code>, specified in &lsquo;<code>stdio.h</code>&rsquo;).  Output will
be passed on to the host system only when the buffer is full, or when
an input operation intervenes.
</p>
<p>You may, if you wish, supply your own buffer by passing a pointer to
it as the argument <var>buf</var>.  It must have size <code>BUFSIZ</code>.  You can
also use <code>NULL</code> as the value of <var>buf</var>, to signal that the
<code>setbuf</code> function is to allocate the buffer.
</p>
<br>
<p><strong>Warnings</strong><br>
You may only use <code>setbuf</code> before performing any file operation other
than opening the file.
</p>
<p>If you supply a non-null <var>buf</var>, you must ensure that the associated
storage continues to be available until you close the stream
identified by <var>fp</var>.
</p>
<br>
<p><strong>Returns</strong><br>
<code>setbuf</code> does not return a result.
</p>
<br>
<p><strong>Portability</strong><br>
Both ANSI C and the System V Interface Definition (Issue 2) require
<code>setbuf</code>.  However, they differ on the meaning of a <code>NULL</code> buffer
pointer: the SVID issue 2 specification says that a <code>NULL</code> buffer
pointer requests unbuffered output.  For maximum portability, avoid
<code>NULL</code> buffer pointers.
</p>
<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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