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194 lines
5.5 KiB
Groff
194 lines
5.5 KiB
Groff
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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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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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.TH SETBUF 3 "15 September 1997" GNO "Library Routines"
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.SH NAME
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.BR setbuf ,
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.BR setbuffer ,
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.BR setlinebuf ,
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.BR setvbuf
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\- stream buffering operations
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.SH SYNOPSIS
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#include <stdio.h>
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.sp 1
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void \fBsetbuf\fR (FILE *\fIstream\fR, char *\fIbuf\fR);
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.br
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void \fBsetbuffer\fR (FILE *\fIstream\fR, char *\fIbuf\fR, size_t \fIsize\fR);
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.sp 1
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int \fBsetlinebuf\fR (FILE *\fIstream\fR);
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.sp 1
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int \fBsetvbuf\fR (FILE *\fIstream\fR, char *\fIbuf\fR, int \fImode\fR, size_t \fIsize\fR);
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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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.BR fflush (3)
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may be used to force the block out early.
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(See
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.BR fclose (3).)
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.LP
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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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.BR 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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.IR stdout
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normally does) it is line buffered.
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The standard error stream
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.IR stderr
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is always unbuffered.
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.LP
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The
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.BR 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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.I mode
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parameter must be one of the following three macros:
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.RS
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.nf
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\fB_IONBF\fR unbuffered
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\fB_IOLBF\fR line buffered
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\fB_IOFBF\fR fully buffered
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.fi
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.RE
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.LP
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The
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.I 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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.I buf
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argument should point to a buffer at least
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.I 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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.I size
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argument
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is not zero but
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.I buf
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is
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.BR 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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.BR NULL
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buffer.)
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.LP
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The
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.BR 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 I/O is performed.
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.LP
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The other three calls are, in effect, simply aliases for calls to
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.BR setvbuf .
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Except for the lack of a return value, the
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.BR setbuf
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function is exactly equivalent to the call
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.nf
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setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
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.fi
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The
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.BR 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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.BR BUFSIZ .
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The
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.BR setlinebuf
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function
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is exactly equivalent to the call:
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.nf
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setvbuf(stream, (char *)NULL, _IOLBF, 0);
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.fi
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.SH RETURN VALUES
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The
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.BR setvbuf
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function returns 0 on success, or
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.BR 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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.LP
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The
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.BR setlinebuf
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function returns what the equivalent
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.BR setvbuf
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would have returned.
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.SH SEE ALSO
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.BR fopen (3),
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.BR fclose (3),
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.BR fread (3),
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.BR malloc (3),
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.BR puts (3),
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.BR printf (3)
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.SH STANDARDS
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The
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.BR setbuf
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and
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.BR setvbuf
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functions
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conform to ANSI/C.
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.SH BUGS
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The
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.BR setbuffer
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and
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.BR setlinebuf
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functions are not portable to versions of BSD before 4.2BSD.
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On 4.2BSD and 4.3BSD systems,
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.BR setbuf
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always uses a suboptimal buffer size and should be avoided.
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