setbuf(3) — Linux manual pages

Name

setbuf, setbuffer, setlinebuf, setvbuf — stream buffering operations

Synopsis

#include <stdio.h>

`void setbuf(`	FILE *	`stream`,
	char *	`buf)`;

`void setbuffer(`	FILE *	`stream`,
	char *	`buf`,
	size_t	`size)`;

void setlinebuf( FILE * stream);

`int setvbuf(`	FILE *	`stream`,
	char *	`buf`,
	int	`mode`,
	size_t	`size)`;

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 fflush(3) may be used to force the block out early. (See fclose(3).) Normally all files are block buffered. When the first I/O operation occurs on a file, malloc(3) is called, and a buffer is obtained. If a stream refers to a terminal (as stdout normally does) it is line buffered. The standard error stream stderr is always unbuffered by default.

The setvbuf() function may be used on any open stream to change its buffer. The mode parameter must be one of the following three macros:

_IONBF

unbuffered

_IOLBF

line buffered

_IOFBF

fully buffered

Except for unbuffered files, the buf argument should point to a buffer at least size bytes long; this buffer will be used instead of the current buffer. If the argument buf is NULL, only the mode is affected; a new buffer will be allocated on the next read or write operation. The setvbuf() function may only be used after opening a stream and before any other operations have been performed on it.

The other three calls are, in effect, simply aliases for calls to setvbuf(). The setbuf() function is exactly equivalent to the call

setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);

The setbuffer() function is the same, except that the size of the buffer is up to the caller, rather than being determined by the default BUFSIZ. The setlinebuf() function is exactly equivalent to the call:

setvbuf(stream, (char *) NULL, _IOLBF, 0);

RETURN VALUE

The function setvbuf() returns 0 on success. It can return any value on failure, but returns non-zero when mode is invalid or the request cannot be honoured. It may set errno on failure. The other functions are void.

CONFORMING TO

The setbuf() and setvbuf() functions conform to C89 and C99.

BUGS

The setbuffer() and setlinebuf() functions are not portable to versions of BSD before 4.2BSD, and are available under Linux since libc 4.5.21. On 4.2BSD and 4.3BSD systems, setbuf() always uses a suboptimal buffer size and should be avoided.

You must make sure that both buf and the space it points to still exist by the time stream is closed, which also happens at program termination.

For example, the following is illegal:

#include <stdio.h>

int
main(void)
{
    char buf[BUFSIZ];
    setbuf(stdin, buf);
    printf("Hello, world!\n");
    return 0;
}

  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
Correction,  Sun, 11 Apr 1999 15:55:18,
    Martin Vicente <martin@netadmin.dgac.fr>
Correction,  2000-03-03, Andreas Jaeger <aj@suse.de>
Added return value for setvbuf, aeb,

Prev	Up	Next
setaliasent	Home	setenv