214 lines
5.4 KiB
Groff
214 lines
5.4 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The 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.
|
|
.\" 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 8.1 (Berkeley) 6/4/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd June 4, 1993
|
|
.Dt SETBUF 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm setbuf ,
|
|
.Nm setbuffer ,
|
|
.Nm setlinebuf ,
|
|
.Nm setvbuf
|
|
.Nd stream buffering operations
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In stdio.h
|
|
.Ft void
|
|
.Fn setbuf "FILE * restrict stream" "char * restrict buf"
|
|
.Ft void
|
|
.Fn setbuffer "FILE *stream" "char *buf" "int size"
|
|
.Ft int
|
|
.Fn setlinebuf "FILE *stream"
|
|
.Ft int
|
|
.Fn setvbuf "FILE * restrict stream" "char * restrict buf" "int mode" "size_t size"
|
|
.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
|
|
.Dv stdin ) .
|
|
The function
|
|
.Xr fflush 3
|
|
may be used to force the block out early.
|
|
(See
|
|
.Xr fclose 3 . )
|
|
.Pp
|
|
Normally all files are block buffered.
|
|
When the first
|
|
.Tn I/O
|
|
operation occurs on a file,
|
|
.Xr malloc 3
|
|
is called,
|
|
and an optimally-sized buffer is obtained.
|
|
If a stream refers to a terminal
|
|
(as
|
|
.Dv stdout
|
|
normally does) it is line buffered.
|
|
The standard error stream
|
|
.Dv stderr
|
|
is always unbuffered.
|
|
Note that these defaults may be altered using the
|
|
.Xr stdbuf 1
|
|
utility.
|
|
.Pp
|
|
The
|
|
.Fn setvbuf
|
|
function
|
|
may be used to alter the buffering behavior of a stream.
|
|
The
|
|
.Fa mode
|
|
argument must be one of the following three macros:
|
|
.Bl -tag -width _IOFBF -offset indent
|
|
.It Dv _IONBF
|
|
unbuffered
|
|
.It Dv _IOLBF
|
|
line buffered
|
|
.It Dv _IOFBF
|
|
fully buffered
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fa size
|
|
argument may be given as zero
|
|
to obtain deferred optimal-size buffer allocation as usual.
|
|
If it is not zero,
|
|
then except for unbuffered files, the
|
|
.Fa buf
|
|
argument should point to a buffer at least
|
|
.Fa size
|
|
bytes long;
|
|
this buffer will be used instead of the current buffer.
|
|
If
|
|
.Fa buf
|
|
is not
|
|
.Dv NULL ,
|
|
it is the caller's responsibility to
|
|
.Xr free 3
|
|
this buffer after closing the stream.
|
|
(If the
|
|
.Fa size
|
|
argument
|
|
is not zero but
|
|
.Fa buf
|
|
is
|
|
.Dv NULL ,
|
|
a buffer of the given size will be allocated immediately,
|
|
and released on close.
|
|
This is an extension to ANSI C;
|
|
portable code should use a size of 0 with any
|
|
.Dv NULL
|
|
buffer.)
|
|
.Pp
|
|
The
|
|
.Fn setvbuf
|
|
function may be used at any time,
|
|
but may have peculiar side effects
|
|
(such as discarding input or flushing output)
|
|
if the stream is ``active''.
|
|
Portable applications should call it only once on any given stream,
|
|
and before any
|
|
.Tn I/O
|
|
is performed.
|
|
.Pp
|
|
The other three calls are, in effect, simply aliases for calls to
|
|
.Fn setvbuf .
|
|
Except for the lack of a return value, the
|
|
.Fn setbuf
|
|
function is exactly equivalent to the call
|
|
.Pp
|
|
.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
|
|
.Pp
|
|
The
|
|
.Fn setbuffer
|
|
function
|
|
is the same, except that the size of the buffer is up to the caller,
|
|
rather than being determined by the default
|
|
.Dv BUFSIZ .
|
|
The
|
|
.Fn setlinebuf
|
|
function
|
|
is exactly equivalent to the call:
|
|
.Pp
|
|
.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);"
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn setvbuf
|
|
function returns 0 on success, or
|
|
.Dv EOF
|
|
if the request cannot be honored
|
|
(note that the stream is still functional in this case).
|
|
.Pp
|
|
The
|
|
.Fn setlinebuf
|
|
function returns what the equivalent
|
|
.Fn setvbuf
|
|
would have returned.
|
|
.Sh SEE ALSO
|
|
.Xr stdbuf 1 ,
|
|
.Xr fclose 3 ,
|
|
.Xr fopen 3 ,
|
|
.Xr fread 3 ,
|
|
.Xr malloc 3 ,
|
|
.Xr printf 3 ,
|
|
.Xr puts 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn setbuf
|
|
and
|
|
.Fn setvbuf
|
|
functions
|
|
conform to
|
|
.St -isoC .
|
|
.Sh BUGS
|
|
The
|
|
.Fn setbuffer
|
|
and
|
|
.Fn setlinebuf
|
|
functions are not portable to versions of
|
|
.Bx
|
|
before
|
|
.Bx 4.2 .
|
|
On
|
|
.Bx 4.2
|
|
and
|
|
.Bx 4.3
|
|
systems,
|
|
.Fn setbuf
|
|
always uses a suboptimal buffer size and should be avoided.
|