SETBUFFER(3C) Standard C Library Functions SETBUFFER(3C)

NAME

setbuffer, setlinebuf - assign buffering to a stream

SYNOPSIS

#include <stdio.h>

void setbuffer(FILE *iop, char *abuf, size_t asize);


int setlinebuf(FILE *iop);

DESCRIPTION

The setbuffer() and setlinebuf() functions assign buffering to a
stream. 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 and
written as a block; when it is line buffered, characters are saved
until either a NEWLINE is encountered or input is read from stdin.
The fflush(3C) function may be used to force the block out early.
Normally all files are block buffered. A buffer is obtained from
malloc(3C) upon the first getc(3C) or putc(3C) performed on the file.
If the standard stream stdout refers to a terminal, it is line
buffered. The standard stream stderr is unbuffered by default.


The setbuffer() function can be used after a stream iop has been
opened but before it is read or written. It uses the character array
abuf whose size is determined by the asize argument instead of an
automatically allocated buffer. If abuf is the null pointer,
input/output will be completely unbuffered. A manifest constant
BUFSIZ, defined in the <stdio.h> header, tells how large an array is
needed:


char buf[BUFSIZ];


The setlinebuf() function is used to change the buffering on a stream
from block buffered or unbuffered to line buffered. Unlike
setbuffer(), it can be used at any time that the stream iop is
active.


A stream can be changed from unbuffered or line buffered to block
buffered by using freopen(3C). A stream can be changed from block
buffered or line buffered to unbuffered by using freopen(3C) followed
by setbuf(3C) with a buffer argument of NULL.

RETURN VALUES

The setlinebuf() function returns no useful value.

SEE ALSO

fclose(3C), fopen(3C), fread(3C), getc(3C), malloc(3C), printf(3C),
putc(3C), puts(3C), setbuf(3C), setvbuf(3C)

NOTES

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
same block.

May 13, 1997 SETBUFFER(3C)