# 2.11BSD#431 - /usr/man/cat3/setbuffer.0

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

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

    SYNOPSIS
         #include <stdio.h>
         #include <sys/types.h>

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

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

         int
         setlinebuf(stream)
    	    FILE *stream;

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

    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 termi-
         nal 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 an
         optimally-sized 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.

         The setvbuf function may be used to alter the buffering
         behavior of a stream.  The mode parameter must be one of the
         following three macros:

    Printed 11/26/99	  July 28, 1997                         1

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

    	  _IONBF    unbuffered

    	  _IOLBF    line buffered

    	  _IOFBF    fully buffered

         The size parameter may be given as zero to obtain deferred
         optimal-size buffer allocation as usual.  If it is not zero,
         then 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 size argu-
         ment is not zero but buf is NULL, a buffer of the given size
         will be allocated immediately, and released on close.  This
         is an extension to ANSI C; portable code should use a size
         of 0 with any NULL buffer.)

         The setvbuf function may be used at any time, but may have
         peculiar side effects (such as discarding input or flushing
         output) if the stream is ``active''.  Portable applications
         should call it only once on any given stream, and before any
         I/O is performed.

         The other three calls are, in effect, simply aliases for
         calls to setvbuf.	Except for the lack of a return value,
         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);

    RETURN VALUES
         The setvbuf function returns 0 on success, or EOF if the
         request cannot be honored (note that the stream is still
         functional in this case).

         The setlinebuf function returns what the equivalent setvbuf
         would have returned.

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

    STANDARDS
         The setbuf and setvbuf functions conform to ANSI C
         X3.159-1989 (``ANSI C'').

    BUGS
         The setbuffer and setlinebuf functions are not portable to

    Printed 11/26/99	  July 28, 1997                         2

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

         versions of BSD before 4.2BSD.  On 2BSD systems, setbuf
         always uses a 1kb buffer size.

    Printed 11/26/99	  July 28, 1997                         3

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