203 lines
5.3 KiB
Groff
203 lines
5.3 KiB
Groff
.\" $NetBSD: setbuf.3,v 1.13 2003/08/07 16:43:31 agc Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)setbuf.3 8.1 (Berkeley) 6/4/93
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.\"
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.Dd June 4, 1993
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.Dt SETBUF 3
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.Os
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.Sh NAME
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.Nm setbuf ,
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.Nm setbuffer ,
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.Nm setlinebuf ,
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.Nm setvbuf
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.Nd stream buffering operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft void
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.Fn setbuf "FILE * restrict stream" "char * restrict buf"
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.Ft void
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.Fn setbuffer "FILE *stream" "char *buf" "size_t size"
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.Ft int
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.Fn setlinebuf "FILE *stream"
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.Ft int
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.Fn setvbuf "FILE * restrict stream" "char * restrict buf" "int mode" "size_t size"
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.Sh DESCRIPTION
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The three types of buffering available are unbuffered, block buffered,
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and line buffered.
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When an output stream is unbuffered, information appears on the
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destination file or terminal as soon as written;
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when it is block buffered many characters are saved up and written as a block;
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when it is line buffered characters are saved up until a newline is
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output or input is read from any stream attached to a terminal device
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(typically stdin).
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The function
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.Xr fflush 3
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may be used to force the block out early.
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(See
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.Xr fclose 3 . )
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.Pp
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Normally all files are block buffered.
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When the first
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.Tn I/O
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operation occurs on a file,
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.Xr malloc 3
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is called,
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and an optimally-sized buffer is obtained.
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If a stream refers to a terminal
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(as
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.Em stdout
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normally does) it is line buffered.
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The standard error stream
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.Em stderr
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is initially unbuffered.
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.Pp
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The
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.Fn setvbuf
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function
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may be used to alter the buffering behavior of a stream.
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The
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.Fa mode
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parameter must be one of the following three macros:
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.Bl -tag -width _IOFBF -offset indent
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.It Dv _IONBF
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unbuffered
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.It Dv _IOLBF
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line buffered
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.It Dv _IOFBF
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fully buffered
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.El
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.Pp
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The
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.Fa size
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parameter may be given as zero
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to obtain deferred optimal-size buffer allocation as usual.
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If it is not zero,
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then except for unbuffered files, the
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.Fa buf
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argument should point to a buffer at least
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.Fa size
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bytes long;
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this buffer will be used instead of the current buffer.
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(If the
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.Fa size
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argument
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is not zero but
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.Fa buf
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is
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.Dv NULL ,
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a buffer of the given size will be allocated immediately,
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and released on close.
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This is an extension to ANSI C;
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portable code should use a size of 0 with any
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.Dv NULL
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buffer.)
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.Pp
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The
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.Fn setvbuf
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function may be used at any time,
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but may have peculiar side effects
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(such as discarding input or flushing output)
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if the stream is ``active''.
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Portable applications should call it only once on any given stream,
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and before any
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.Tn I/O
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is performed.
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.Pp
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The other three calls are, in effect, simply aliases for calls to
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.Fn setvbuf .
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Except for the lack of a return value, the
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.Fn setbuf
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function is exactly equivalent to the call
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.Pp
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.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
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.Pp
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The
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.Fn setbuffer
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function
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is the same, except that the size of the buffer is up to the caller,
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rather than being determined by the default
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.Dv BUFSIZ .
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The
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.Fn setlinebuf
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function
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is exactly equivalent to the call:
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.Pp
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.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);"
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.Sh RETURN VALUES
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The
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.Fn setvbuf
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function returns 0 on success, or
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.Dv EOF
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if the request cannot be honored
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(note that the stream is still functional in this case).
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.Pp
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The
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.Fn setlinebuf
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function returns what the equivalent
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.Fn setvbuf
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would have returned.
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.Sh SEE ALSO
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.Xr fclose 3 ,
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.Xr fopen 3 ,
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.Xr fread 3 ,
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.Xr malloc 3 ,
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.Xr printf 3 ,
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.Xr puts 3
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.Sh STANDARDS
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The
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.Fn setbuf
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and
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.Fn setvbuf
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functions
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conform to
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.St -ansiC .
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.Sh BUGS
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The
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.Fn setbuffer
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and
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.Fn setlinebuf
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functions are not portable to versions of
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.Bx
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before
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.Bx 4.2 .
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On
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.Bx 4.2
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and
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.Bx 4.3
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systems,
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.Fn setbuf
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always uses a suboptimal buffer size and should be avoided.
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