setbuf(3s)setbuf(3s)Name
setbuf, setbuffer, setlinebuf, setvbuf - assign buffering to a stream
Syntax
#include <stdio.h>
void setbuf(stream, buf)
FILE *stream;
char *buf;
void setbuffer(stream, buf, size)
FILE *stream;
char *buf;
int size;
void setlinebuf(stream)
FILE *stream;
int setvbuf(stream, buf, type, size)
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 new line is
encountered or input is read from stdin. The routine may be used to
force the block out early. Normally all files are block buffered. For
further information, see A buffer is obtained from upon the first or on
the file. If the standard stream stdout refers to a terminal it is
line buffered. The standard stream stderr is always unbuffered.
The routine is used after a stream has been opened but before it is
read or written. The character array buf is used instead of an auto‐
matically 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];
The routine, an alternate form of 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 automati‐
cally allocated buffer. If buf is the constant pointer NULL,
input/output will be completely unbuffered.
The routine is used to change stdout or stderr from block buffered or
unbuffered to line buffered. Unlike and it can be used at any time
that the file descriptor is active.
The routine may be used after a stream has been opened but before it is
read or written. Type determines how stream will be buffered. Legal
values for type, defined in stdio.h are:
_IOFBF causes input/output to be fully buffered.
_IOLBF causes output to be line buffered; the buffer will be
flushed when a new line is written, the buffer is full,
or input is requested.
_IONBF causes input/output to be completely unbuffered.
If buf is not the NULL pointer, the array it points to will be used for
buffering, instead of an automatically allocated buffer. The size
specifies the size of the buffer to be used. The constant BUFSIZ in
<stdio.h> is suggested as a good buffer size. If input/output is
unbuffered, buf and size are ignored.
By default, output to a terminal is line buffered and all other
input/output is fully buffered.
A file can be changed from unbuffered or line buffered to block
buffered by using For further information, see A file can be changed
from block buffered or line buffered to unbuffered by using followed by
with a buffer argument of NULL.
Restrictions
The standard error stream should be line buffered by default.
The and functions are not portable to non 4.2 BSD versions of UNIX.
See Alsomalloc(3), fclose(3s), fopen(3s), fread(3s), getc(3s), printf(3s),
putc(3s), puts(3s).
setbuf(3s)