SETBUF(3S)																SETBUF(3S)

NAME

       setbuf, setbuffer, setlinebuf - assign buffering to a stream

SYNOPSIS

       #include <stdio.h>

       setbuf(stream, buf)
       FILE *stream;
       char *buf;

       setbuffer(stream, buf, size)
       FILE *stream;
       char *buf;
       int size;

       setlinebuf(stream)
       FILE *stream;

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 newline is encountered or input is read from stdin.  Fflush (see
       fclose(3S)) may be used to force the block out early.  Normally all files are block buffered.  A buffer is obtained from malloc(3) upon the
       first getc or putc(3S) on the file.  If the standard stream stdout refers to a terminal it is line buffered.  The standard stream stderr is
       always unbuffered.

       Setbuf is used after a stream has been opened but before it is read or written.	The character array buf is used instead  of  an  automati-
       cally 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];

       Setbuffer, an alternate form of setbuf, 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 automatically allocated buffer.  If buf is the constant pointer NULL,
       input/output will be completely unbuffered.

       Setlinebuf is used to change stdout or stderr from block buffered or unbuffered to line buffered.  Unlike setbuf and setbuffer  it  can	be
       used at any time that the file descriptor is active.

       A  file	can  be  changed  from unbuffered or line buffered to block buffered by using freopen (see fopen(3S)).	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.

SEE ALSO

       fopen(3S), getc(3S), putc(3S), malloc(3), fclose(3S), puts(3S), printf(3S), fread(3S)

BUGS

       The standard error stream should be line buffered by default.

       The setbuffer and setlinebuf functions are not portable to non-4.2BSD versions of UNIX.	On 4.2BSD and 4.3BSD systems, setbuf always uses a
       suboptimal buffer size and should be avoided.  Setbuffer is not usually needed as the default file I/O buffer sizes are optimal.

4th Berkeley Distribution					   May 12, 1986 							SETBUF(3S)