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NetBSD 6.1.5 - man page for setbuf (netbsd section 3)

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

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

     Standard C Library (libc, -lc)

     #include <stdio.h>

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

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

     setlinebuf(FILE *stream);

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

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

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

     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.

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

     The setbuf() and setvbuf() functions conform to ANSI X3.159-1989 (``ANSI C89'').

     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.

BSD					   June 4, 1993 				      BSD

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