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 <h3 class="section">4.57 <code>setvbuf</code>&mdash;specify file or stream buffering</h3>

 <p><a name="index-setvbuf-266"></a><strong>Synopsis</strong>
 <pre class="example">     #include &lt;stdio.h&gt;
      int setvbuf(FILE *<var>fp</var>, char *<var>buf</var>,
          int <var>mode</var>, size_t <var>size</var>);

 </pre>
    <p><strong>Description</strong><br>
 Use <code>setvbuf</code> to specify what kind of buffering you want for the
 file or stream identified by <var>fp</var>, by using one of the following
 values (from <code>stdio.h</code>) as the <var>mode</var> argument:

      <dl>
 <dt><code>_IONBF</code><dd>Do not use a buffer: send output directly to the host system for the
 file or stream identified by <var>fp</var>.

      <br><dt><code>_IOFBF</code><dd>Use full output buffering: output will be passed on to the host system
 only when the buffer is full, or when an input operation intervenes.

      <br><dt><code>_IOLBF</code><dd>Use line buffering: pass on output to the host system at every
 newline, as well as when the buffer is full, or when an input
 operation intervenes.
 </dl>

    <p>Use the <var>size</var> argument to specify how large a buffer you wish.  You
 can supply the buffer itself, if you wish, by passing a pointer to a
 suitable area of memory as <var>buf</var>.  Otherwise, you may pass <code>NULL</code>
 as the <var>buf</var> argument, and <code>setvbuf</code> will allocate the buffer.

    <p><br>
 <strong>Warnings</strong><br>
 You may only use <code>setvbuf</code> before performing any file operation other
 than opening the file.

    <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>
 <strong>Returns</strong><br>
 A <code>0</code> result indicates success, <code>EOF</code> failure (invalid <var>mode</var> or
 <var>size</var> can cause failure).

    <p><br>
 <strong>Portability</strong><br>
 Both ANSI C and the System V Interface Definition (Issue 2) require
 <code>setvbuf</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>Both specifications describe the result on failure only as a
 nonzero value.

    <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>.

    <p><br>

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	<h3 class="section">4.57 <code>setvbuf</code>—specify file or stream buffering</h3>

	<p><a name="index-setvbuf-266"></a><strong>Synopsis</strong>
	<pre class="example"> #include <stdio.h>
	int setvbuf(FILE <var>fp</var>, char <var>buf</var>,
	int <var>mode</var>, size_t <var>size</var>);

	</pre>
	<p><strong>Description</strong><br>
	Use <code>setvbuf</code> to specify what kind of buffering you want for the
	file or stream identified by <var>fp</var>, by using one of the following
	values (from <code>stdio.h</code>) as the <var>mode</var> argument:

	<dl>
	<dt><code>_IONBF</code><dd>Do not use a buffer: send output directly to the host system for the
	file or stream identified by <var>fp</var>.

	<br><dt><code>_IOFBF</code><dd>Use full output buffering: output will be passed on to the host system
	only when the buffer is full, or when an input operation intervenes.

	<br><dt><code>_IOLBF</code><dd>Use line buffering: pass on output to the host system at every
	newline, as well as when the buffer is full, or when an input
	operation intervenes.
	</dl>

	<p>Use the <var>size</var> argument to specify how large a buffer you wish. You
	can supply the buffer itself, if you wish, by passing a pointer to a
	suitable area of memory as <var>buf</var>. Otherwise, you may pass <code>NULL</code>
	as the <var>buf</var> argument, and <code>setvbuf</code> will allocate the buffer.

	<p><br>
	<strong>Warnings</strong><br>
	You may only use <code>setvbuf</code> before performing any file operation other
	than opening the file.

	<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>
	<strong>Returns</strong><br>
	A <code>0</code> result indicates success, <code>EOF</code> failure (invalid <var>mode</var> or
	<var>size</var> can cause failure).

	<p><br>
	<strong>Portability</strong><br>
	Both ANSI C and the System V Interface Definition (Issue 2) require
	<code>setvbuf</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>Both specifications describe the result on failure only as a
	nonzero value.

	<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>.

	<p><br>

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