4.4BSD/usr/share/man/cat3/setbuffer.0

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

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

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ssttddiioo..hh>>

     _v_o_i_d
     sseettbbuuff(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f);

     _v_o_i_d
     sseettbbuuffffeerr(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f, _s_i_z_e___t _s_i_z_e);

     _i_n_t
     sseettlliinneebbuuff(_F_I_L_E _*_s_t_r_e_a_m);

     _i_n_t
     sseettvvbbuuff(_F_I_L_E _*_s_t_r_e_a_m, _c_h_a_r _*_b_u_f, _i_n_t _m_o_d_e, _s_i_z_e___t _s_i_z_e);

DDEESSCCRRIIPPTTIIOONN
     The three types of buffering available are unbuffered, block buffered,
     and line buffered.  When an output stream is unbuffered, information ap-
     pears 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 oc-
     curs on a file, malloc(3) is called, and an optimally-sized buffer is ob-
     tained.  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 sseettvvbbuuff() 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:

           _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 un-
     buffered 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 argument 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 exten-
     sion 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);

RREETTUURRNN VVAALLUUEESS
     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.

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

SSTTAANNDDAARRDDSS
     The sseettbbuuff() and sseettvvbbuuff() functions conform to ANSI C X3.159-1989
     (``ANSI C '').

BBUUGGSS
     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.

4th Berkeley Distribution        June 4, 1993                                2