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.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)setbuf.3 6.10 (Berkeley) 6/29/91
.\"
.\" Converted for Linux, Mon Nov 29 14:55:24 1993, faith@cs.unc.edu
.\" Added section to BUGS, Sun Mar 12 22:28:33 MET 1995,
.\" Thomas.Koenig@ciw.uni-karlsruhe.de
.\"
.TH SETBUF 3 "29 November 1993" "BSD MANPAGE" "Linux Programmer's Manual"
.SH NAME
setbuf, setbuffer, setlinebuf, setvbuf \- stream buffering operations
.SH SYNOPSIS
.na
.B #include <stdio.h>
.sp
.BI "int setbuf(FILE *" stream ", char *" buf );
.br
.BI "int setbuffer(FILE *" stream ", char *" buf ", size_t" size );
.br
.BI "int setlinebuf(FILE *" stream );
.br
.BI "int setvbuf(FILE *" stream ", char *" buf ", int " mode
.BI ", size_t " size );
.ad
.SH DESCRIPTION
The three types of buffering available are unbuffered, block buffered, and
line buffered. When an output stream is unbuffered, information appears on
the destination file or terminal as soon as written; when it is block
buffered many characters are saved up and written as a block; when it is
line buffered characters are saved up until a newline is output or input is
read from any stream attached to a terminal device (typically stdin). The
function
.BR fflush (3)
may be used to force the block out early.
(See
.BR fclose (3).)
Normally all files are block buffered. When the first I/O operation occurs
on a file,
.BR malloc (3)
is called, and a buffer is obtained. If a stream refers to a terminal (as
.I stdout
normally does) it is line buffered. The standard error stream
.I stderr
is always unbuffered by default.
.PP
The
.B setvbuf
function may be used at any time on any open stream to change its buffer.
The
.I mode
parameter must be one of the following three macros:
.RS
.TP
.B _IONBF
unbuffered
.TP
.B _IOLBF
line buffered
.TP
.B _IOFBF
fully buffered
.RE
.PP
Except for unbuffered files, the
.I buf
argument should point to a buffer at least
.I size
bytes long; this buffer will be used instead of the current buffer. If the
argument
.I buf
is
.BR NULL ,
only the mode is affected; a new buffer will be allocated on the next read
or write operation. The
.I setvbuf
function may be used at any time, but can only change the mode of a stream
when it is not ``active'': that is, before any I/O, or immediately after a
call to
.BR fflush .
.PP
The other three calls are, in effect, simply aliases for calls to
.BR setvbuf .
The
.B setbuf
function is exactly equivalent to the call
.PP
.RS
setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
.RE
.PP
The
.B setbuffer
function is the same, except that the size of the buffer is up to the
caller, rather than being determined by the default
.BR BUFSIZ .
The
.B setlinebuf
function is exactly equivalent to the call:
.PP
.RS
setvbuf(stream, (char *)NULL, _IOLBF, 0);
.RE
.SH "SEE ALSO"
.BR fopen "(3), " fclose "(3), " fflush "(3), " fread "(3), " malloc "(3), "
.BR puts "(3), " printf (3)
.SH "CONFORMING TO"
The
.B setbuf
and
.B setvbuf
functions conform to ANSI C3.159-1989 (``ANSI C'').
.SH BUGS
The
.B setbuffer
and
.B setlinebuf
functions are not portable to versions of BSD before 4.2BSD, and may not be
available under Linux. On 4.2BSD and 4.3BSD systems,
.B setbuf
always uses a suboptimal buffer size and should be avoided.
.P
You must make sure that both
.I buf
and the space it points to still exist by the time
.I stream
is closed, which also happens at program termination.
.P
For example, the following is illegal:
.nf
.sp
#include <stdio.h>
int main()
{
char buf[BUFSIZ];
setbuf(stdin, buf);
printf("Hello, world!\\n");
return 0;
}
.fi
.sp
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