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(_s_t_r_e_a_m, _b_u_f)
	    FILE *stream;
	    char *buf;

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

     int
     setlinebuf(_s_t_r_e_a_m)
	    FILE *stream;

     int
     setvbuf(_s_t_r_e_a_m, _b_u_f, _m_o_d_e, _s_i_z_e)
	    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 _s_t_d_o_u_t normally does) it is line buffered.  The
     standard error stream _s_t_d_e_r_r is always unbuffered.

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





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



	  _IONBF    unbuffered

	  _IOLBF    line buffered

	  _IOFBF    fully buffered

     The _s_i_z_e 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 _b_u_f argument should
     point to a buffer at least _s_i_z_e bytes long; this buffer will
     be used instead of the current buffer.  (If the _s_i_z_e argu-
     ment is not zero but _b_u_f 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



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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