setbuf, setbuffer, setlinebuf, setvbuf - assign buffering to a stream
void setbuf(stream, buf)
void setbuffer(stream, buf, size)
int setlinebuf(stream) FILE *stream;
int setvbuf(stream, buf, type, size)
int type, size;
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(3V)) may
be used to force the block out early. A buffer is obtained from mal-
loc(3V) upon the first getc(3V) or putc(3S) on the file. By default,
output to a terminal is line buffered, except for output to the stan-
dard stream stderr which is unbuffered. All other input/output is
setbuf() can be used after a stream has been opened but before it is
read or written. It causes the array pointed to by buf to be used
instead of an automatically allocated buffer. If buf is the NULL
pointer, input/output will be completely unbuffered. A manifest con-
stant BUFSIZ, defined in the <<stdio.h>> header file, tells how big an
array is needed:
setbuffer(), an alternate form of setbuf(), can be used after a stream
has been opened but before it is read or written. It uses the charac-
ter array buf whose size is determined by the size argument instead of
an automatically allocated buffer. If buf is the NULL pointer,
input/output will be completely unbuffered.
setvbuf() can 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 fully buffers the input/output.
_IOLBF line buffers the output; the buffer will be flushed when a NEW-
LINE is written, the buffer is full, or input is requested.
_IONBF completely unbuffers the input/output.
If buf is not the NULL pointer, the array it points to will be used for
buffering, instead of an automatically allocated buffer. size speci-
fies the size of the buffer to be used.
setlinebuf() is used to change the buffering on a stream from block
buffered or unbuffered to line buffered. Unlike setbuf(), setbuffer(),
and setvbuf(), it can be used at any time that the file descriptor is
A file can be changed from unbuffered or line buffered to block
buffered by using freopen() (see fopen(3V)). 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.
SYSTEM V DESCRIPTION
If buf is not NULL and stream refers to a terminal device, setbuf()
sets stream for line buffered input/output.
setlinebuf() returns no useful value.
setvbuf() returns 0 on success. If an illegal value for type or size
is provided, setvbuf() returns a non-zero value. setvbuf()
fclose(3V), fopen(3V), fread(3S), getc(3V), malloc(3V), printf(3V),
A common source of error is allocating buffer space as an "automatic"
variable in a code block, and then failing to close the stream in the
21 January 1990 SETBUF(3V)