SETBUF
Section: C Library Functions (3)
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BSD mandoc
BSD 4
NAME
setbuf
setbuffer
setlinebuf
setvbuf
- stream buffering operations
SYNOPSIS
Fd #include <stdio.h>
Ft int
Fn setbuf FILE *stream char *buf
Ft int
Fn setbuffer FILE *stream char *buf size_t size
Ft int
Fn setlinebuf FILE *stream
Ft int
Fn setvbuf FILE *stream char *buf int mode size_t size
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 stdin).
The function
fflush(3)
may be used to force the block out early.
(See
fclose(3).)
Normally all files are block buffered.
When the first
I/O
operation occurs on a file,
malloc(3)
is called,
and a buffer is obtained.
If a stream refers to a terminal
(as
stdout
normally does) it is line buffered.
The standard error stream
stderr
is always unbuffered.
The
Fn setvbuf
function
may be used at any time on any open stream
to change its buffer.
The
Fa mode
parameter must be one of the following three macros:
- _IONBF
-
unbuffered
- _IOLBF
-
line buffered
- _IOFBF
-
fully buffered
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 the argument
Fa buf
is NULL,
only the mode is affected;
a new buffer will be allocated on the next read or write operation.
The
Fn setvbuf
function
may be used at any time,
but can only change the mode of a stream
when it is not ``active'':
that is, before any
I/O
or immediately after a call to
fflush.
The other three calls are, in effect, simply aliases
for calls to
Fn setvbuf .
The
Fn setbuf
function
is exactly equivalent to the call
setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
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
BUFSIZ
The
Fn setlinebuf
function
is exactly equivalent to the call:
setvbuf(stream, (char *)NULL, _IOLBF, 0);
SEE ALSO
fopen(3),
fclose(3),
fread(3),
malloc(3),
puts(3),
printf(3)
STANDARDS
The
Fn setbuf
and
Fn setvbuf
functions
conform to
St -ansiC .
BUGS
The
Fn setbuffer
and
Fn setlinebuf
functions are not portable to versions of
BSD before
BSD 4.2
On
BSD 4.2
and
BSD 4.3
systems,
Fn setbuf
always uses a suboptimal buffer size and should be avoided.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- SEE ALSO
-
- STANDARDS
-
- BUGS
-
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Time: 06:40:33 GMT, May 19, 2025