setbuffer, setlinebuf - assign buffering to a stream
void setbuffer(FILE *iop, char *abuf, size_t asize);
int setlinebuf(FILE *iop);
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 out-
put stream is unbuffered, information appears on the desti-
nation 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:
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
The setlinebuf() function returns no useful value.
malloc(3C), fclose(3C), fopen(3C), fread(3C), getc(3C),
printf(3C), putc(3C), puts(3C), setbuf(3C), setvbuf(3C)
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.
Man(1) output converted with