SETBUF(3S)SETBUF(3S)NAME
setbuf, setvbuf, setbuffer, setlinebuf - assign buffering to a stream
SYNOPSIS
#include <stdio.h>
void setbuf(FILE *stream, char *buf);
void setvbuf(FILE *stream, char *buf, int mode, size_t size);
setbuffer(stream, buf, size)
FILE *stream;
char *buf;
int size;
setlinebuf(stream)
FILE *stream;
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
encountered or input is read from stdin. Fflush (see fclose(3S)) may
be used to force the block out early. Normally all files are block
buffered. A buffer is obtained from malloc(3) upon the first getc or
putc(3S) on the file. If the standard stream stdout refers to a
terminal it is line buffered. The standard stream stderr is always
unbuffered.
Setbuf is used after a stream has been opened but before it is read or
written. The character array buf is used instead of an automatically
allocated buffer. If buf is the constant pointer NULL, input/output
will be completely unbuffered. A manifest constant BUFSIZ tells how
big an array is needed:
char buf[BUFSIZ];
Setvbuf, an alternate form of setbuf, is used after a stream has been
opened but before it is read or written. The argument mode determines
how the stream will be buffered: _IOFBF causes input/output to be fully
buffered; _IOLBF causes output to be line buffered; _IONBF causes
input/output to be unbuffered. If buf is not a null pointer, the
character array buf whose size is determined by the size argument is
used as the buffer. If buf is the constant pointer NULL, if required,
a buffer will be automatically allocated.
Setbuffer, which is obsoleted by the ANSI C function Setvbuf, is used
after a stream has been opened but before it is read or written. The
character array buf whose size is determined by the size argument is
used instead of an automatically allocated buffer. If buf is the
constant pointer NULL, input/output will be completely unbuffered.
Setlinebuf, which is obsoleted by the ANSI C function Setvbuf, is used
to change stdout or stderr from block buffered or unbuffered to line
buffered. Unlike setbuf and setbuffer it can be used at any time that
the file descriptor is active.
A file can be changed from unbuffered or line buffered to block
buffered by using freopen (see fopen(3S)). A file can be changed from
block buffered or line buffered to unbuffered by using freopen followed
by setbuf with a buffer argument of NULL.
SEE ALSOfopen(3S), getc(3S), putc(3S), malloc(3), fclose(3S), puts(3S),
printf(3S), fread(3S)BUGS
The standard error stream should be line buffered by default.
The setbuffer and setlinebuf functions are not portable to non-4.2BSD
versions of UNIX. On 4.2BSD and 4.3BSD systems, setbuf always uses a
suboptimal buffer size and should be avoided. Setbuffer is not usually
needed as the default file I/O buffer sizes are optimal.
May 12, 1986 SETBUF(3S)
