NAME
setbuf, setvbuf - assign buffering to a stream
SYNOPSIS
#include <stdio.h>
int setbuf(FILE *stream, char *buf)
int setvbuf(FILE *stream, char *buf, int type, 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
encountered or input is read from stdin. Fflush (see
fclose(3)) may be used to force the block out early. Nor-
mally all files are block buffered. A buffer is obtained
from malloc(3) upon the first getc or putc(3) on the file.
If the standard stream stdout refers to a terminal it is
line buffered. The standard stream stderr is always unbuf-
fered.
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 con-
stant pointer NULL, input/output will be completely unbuf-
fered. 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. It has
three uses, depending on the value of the type argument:
setvbuf(stream, buf, _IOFBF, size)
Causes input/output to be fully buffered using the
character array buf whose size is determined by the
size argument. If buf is the constant pointer NULL,
then an automatically allocated buffer will be used.
setvbuf(stream, buf, _IOLBF, size)
Like above, except that output will be line buffered,
i.e. the buffer will be flushed when a newline is writ-
ten, the buffer is full, or input is requested.
setvbuf(stream, buf, _IONBF, size)
Causes input/output to be completely unbuffered. Buf
and size are ignored.
A file can be changed between unbuffered, line buffered, or
block buffered by using freopen (see fopen(3)) followed by
the appropriate setvbuf call.
SEE ALSO
fopen(3), getc(3), putc(3), malloc(3), fclose(3), puts(3),
printf(3), fread(3).