.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" %sccs.include.redist.man%
.\" @(#)setbuf.3 6.11 (Berkeley) %G%
.Nd stream buffering operations
.Fn setbuf "FILE *stream" "char *buf"
.Fn setbuffer "FILE *stream" "char *buf" "size_t size"
.Fn setlinebuf "FILE *stream"
.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size"
The three types of buffering available are unbuffered, block 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
may be used to force the block out early.
Normally all files are block buffered.
operation occurs on a file,
and an optimally-sized buffer is obtained.
If a stream refers to a terminal
normally does) it is line buffered.
The standard error stream
may be used to alter the buffering behavior of a stream.
parameter must be one of the following three macros:
.Bl -tag -width _IOFBF -offset indent
parameter may be given as zero
to obtain deferred optimal-size buffer allocation as usual.
then except for unbuffered files, the
argument should point to a buffer at least
this buffer will be used instead of the current buffer.
a buffer of the given size will be allocated immediately,
This is an extension to ANSI C;
portable code should use a size of 0 with any
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,
The other three calls are, in effect, simply aliases for calls to
Except for the lack of a return value, the
function is exactly equivalent to the call
.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
is the same, except that the size of the buffer is up to the caller,
rather than being determined by the default
is exactly equivalent to the call:
.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);"
function returns 0 on success, or
if the request cannot be honored
(note that the stream is still functional in this case).
function returns what the equivalent
functions are not portable to versions of
always uses a suboptimal buffer size and should be avoided.