setbuf man page on 4.4BSD

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SETBUF(3)		 BSD Library Functions 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);

     int
     setlinebuf(FILE *stream);

     int
     setvbuf(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 out‐
     put or input is read from any stream attached to a terminal device (typi‐
     cally 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:

	   _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 argument is not zero but buf is NULL, a buffer of the given size
     will be allocated immediately, and released on close.  This is an exten‐
     sion to ANSI C; portable code should use a size of 0 with any NULL buf‐
     fer.)

     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 X3.159-1989
     (“ANSI C89”).

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

4th Berkeley Distribution	 June 4, 1993	     4th Berkeley Distribution
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