SETBUF(3)						   BSD Library Functions Manual 						 SETBUF(3)

NAME

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

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdio.h>

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

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

     int
     setlinebuf(FILE *stream);

     int
     setvbuf(FILE * restrict stream, char * restrict 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 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 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.  Note that these defaults may be altered using the stdbuf(1) utility.

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

	   _IONBF  unbuffered

	   _IOLBF  line buffered

	   _IOFBF  fully buffered

     The size argument 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 buf is not NULL, it is the caller's responsibility to free(3) this buffer after closing the stream.  (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 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

     stdbuf(1), fclose(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

STANDARDS

     The setbuf() and setvbuf() functions conform to ISO/IEC 9899:1990 (``ISO C90'').

BUGS

     setbuf() usually uses a suboptimal buffer size and should be avoided.

BSD
								 February 18, 2013							       BSD