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 writ‐
ten 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 automati‐
cally 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 ALSOmalloc(3C), fclose(3C), fopen(3C), fread(3C), getc(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.
SunOS 5.10 13 May 1997 setbuffer(3C)
