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

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

SYNOPSIS
       #include	<stdio.h>

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

       void setbuffer(FILE *stream, char *buf, size_t size);

       void setlinebuf(FILE *stream);

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

   Feature Test	Macro Requirements for glibc (see feature_test_macros(7)):

       setbuffer(), setlinebuf(): _BSD_SOURCE

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
       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 obtained.  If a stream refers to	a terminal (as
       stdout  normally	does), it is line buffered.  The standard error	stream
       stderr is always	unbuffered by default.

       The setvbuf() function may be used on any open  stream  to  change  its
       buffer.	The mode argument 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  cur-
       rent 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	only after opening a stream and	before
       any other operations have been performed	on it.

       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 buf-
       fer is up to the	caller,	rather than being determined  by  the  default
       BUFSIZ.	The setlinebuf() function is exactly equivalent	to the call:

	   setvbuf(stream, NULL, _IOLBF, 0);

RETURN VALUE
       The  function  setvbuf()	 returns  0 on success.	 It returns nonzero on
       failure (mode is	invalid	or the request cannot be honored).  It may set
       errno on	failure.

       The other functions do not return a value.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The  setbuf(),  setbuffer(),  setlinebuf(), and setvbuf() functions are
       thread-safe.

CONFORMING TO
       The setbuf() and	setvbuf() functions conform to C89 and C99.

BUGS
       You must	make sure that the space that buf points to  still  exists  by
       the  time  stream is closed, which also happens at program termination.
       For example, the	following is invalid:

       #include	<stdio.h>

       int
       main(void)
       {
	   char	buf[BUFSIZ];
	   setbuf(stdin, buf);
	   printf("Hello, world!\n");
	   return 0;
       }

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

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-08-19			     SETBUF(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON

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