162 lines
4.6 KiB
Groff
162 lines
4.6 KiB
Groff
.\" $OpenBSD: setvbuf.3,v 1.5 2022/07/25 02:25:55 jsg 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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.Dd $Mdocdate: July 25 2022 $
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.Dt SETVBUF 3
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.Os
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.Sh NAME
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.Nm setvbuf
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.Nd stream buffering operations
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.Sh SYNOPSIS
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.In stdio.h
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.Ft int
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.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size"
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.Sh DESCRIPTION
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The three types of stream 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 line buffered, characters are saved up until a newline
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.Pq Ql \en
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is output or input is read from any stream attached to a terminal device
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(typically
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.Em stdin ) .
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.Pp
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The
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.Xr fflush 3
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function may be used to force the block out early.
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.Pp
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Normally, all files are block buffered.
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When the first I/O 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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.Pp
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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 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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.Pp
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.Bl -tag -width _IOFBF -offset indent -compact
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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, 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
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.Dq active .
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Portable applications should call it only once on any given stream,
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and before any I/O is performed.
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.Sh RETURN VALUES
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Upon successful completion, a value of 0 is returned.
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If
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.Fa mode
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is invalid or if the request cannot be honored, a non-zero value is returned,
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possibly setting
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.Va errno
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to indicate the error.
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The stream is not modified in the error case.
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.Sh ERRORS
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The
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.Fn setvbuf
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa stream
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specified is not associated with a valid file descriptor.
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.El
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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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.Xr setbuf 3
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.Sh STANDARDS
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The
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.Fn setvbuf
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function conforms to
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.St -isoC-99 .
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.Sh HISTORY
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The
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.Fn setvbuf
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function first appeared in
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.At V.2
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and was reimplemented for
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.Bx 4.3 Net/2 .
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