SETBUF(3)                   BSD Programmer's Manual                  SETBUF(3)

NAME
     setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations

SYNOPSIS
     #include <stdio.h>

     int
     setbuf(FILE *stream, char *buf)

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

     int
     setlinebuf(FILE *stream)

     int
     setvbuf(FILE *stream, char *buf, int mode, sizet size)

DESCRIPTION
     The three types of buffering available are unbuffered, block buffered,
     and line buffered.  When an output stream is unbuffered, information ap-
     pears 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 output or
     input is read from any stream attached to a terminal device (typically
     stdin).  The function fflush(3) may be used to force the block out early.
     (See fclose(3).)  Normally all files are block buffered.  When the first
     I/O operation occurs on a file, malloc(3) is called, and a buffer is ob-
     tained.  If a stream refers to a terminal (as stdout normally does) it is
     line buffered.  The standard error stream stderr is always unbuffered.

     The setvbuf() function may be used at any time on any open stream to
     change its buffer.  The mode parameter must be one of the following three
     macros:

           _IONBF  unbuffered

           _IOLBF  line buffered

           _IOFBF  fully buffered

     Except for unbuffered files, the buf argument should point to a buffer at
     least size bytes long; this buffer will be used instead of the current
     buffer.  If the argument buf is NULL, only the mode is affected; a new
     buffer will be allocated on the next read or write operation.  The
     setvbuf() function may be used at any time, but can only change the mode
     of a stream when it is not ``active'': that is, before any I/O, or imme-
     diately after a call to fflush.

     The other three calls are, in effect, simply aliases for calls to
     setvbuf().  The setbuf() function is exactly equivalent to the call

           setvbuf(stream, buf, buf ? _IOFBF: _IONBF, BUFSIZ);

     The setbuffer() function is the same, except that the size of the buffer
     is up to the caller, rather than being determined by the default BUFSIZ.
     The setlinebuf() function is exactly equivalent to the call:

           setvbuf(stream, (char *)NULL, _IOLBF, 0);

SEE ALSO
     fopen(3),  fclose(3),  fread(3),  malloc(3),  puts(3),  printf(3)

STANDARDS

     The setbuf() and setvbuf() functions conform to ANSI C3.159-1989 (``ANSI
     C'').

BUGS
     The setbuffer() and setlinebuf() functions are not portable to versions
     of BSD UNIX before 4.2BSD. On 4.2BSD and 4.3BSD systems, setbuf() always
     uses a suboptimal buffer size and should be avoided.

4th Berkeley Distribution       March 26, 1993                               2