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

NAME
     sseettbbuuff, sseettbbuuffffeerr, sseettlliinneebbuuff, sseettvvbbuuff - stream buffering operations

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

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

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

     int
     sseettlliinneebbuuff(FILE *stream);

     int
     sseettvvbbuuff(FILE * restrict stream, char * restrict buf, int mode,
         sizet 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 sseettvvbbuuff() 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 sseettvvbbuuff() 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
     sseettvvbbuuff().  Except for the lack of a return value, the sseettbbuuff() function
     is exactly equivalent to the call

           setvbuf(stream, buf, buf ? IOFBF : IONBF, BUFSIZ);

     The sseettbbuuffffeerr() 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 sseettlliinneebbuuff() function is exactly equivalent to the call:

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

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

     The sseettlliinneebbuuff() function returns what the equivalent sseettvvbbuuff() would
     have returned.

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

STANDARDS     The sseettbbuuff() and sseettvvbbuuff() functions conform to ISO/IEC 9899:1990
     (``ISO C90'').

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

BSD                              June 4, 1993                              BSD