6486b015fc
This tool changes the default buffering behaviour of standard stdio streams. It only works on dynamic binaries. To make it work for static ones it would require cluttering stdio because there no single entry point. PR: 166660 Reviewed by: current@, jhb Approved by: kib (mentor) MFC after: 1 week
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 maybe 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.
|