4.3BSD-UWisc/man/cat3/setbuf.3s

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



NAME
     setbuf, setbuffer, setlinebuf - assign buffering to a stream

SYNOPSIS
     #include <stdio.h>

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

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

     setlinebuf(stream)
     FILE *stream;

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
     encountered or input is read from stdin.  _F_f_l_u_s_h (see
     _f_c_l_o_s_e(3S)) may be used to force the block out early.  Nor-
     mally all files are block buffered.  A buffer is obtained
     from _m_a_l_l_o_c(3) upon the first _g_e_t_c or _p_u_t_c(3S) on the file.
     If the standard stream stdout refers to a terminal it is
     line buffered.  The standard stream stderr is always unbuf-
     fered.

     _S_e_t_b_u_f is used after a stream has been opened but before it
     is read or written.  The character array _b_u_f is used instead
     of an automatically allocated buffer.  If _b_u_f is the con-
     stant pointer NULL, input/output will be completely unbuf-
     fered.  A manifest constant BUFSIZ tells how big an array is
     needed:

          char buf[BUFSIZ];

     _S_e_t_b_u_f_f_e_r, an alternate form of _s_e_t_b_u_f, is used after a
     stream has been opened but before it is read or written.
     The character array _b_u_f whose size is determined by the _s_i_z_e
     argument is used instead of an automatically allocated
     buffer.  If _b_u_f is the constant pointer NULL, input/output
     will be completely unbuffered.

     _S_e_t_l_i_n_e_b_u_f is used to change _s_t_d_o_u_t or _s_t_d_e_r_r from block
     buffered or unbuffered to line buffered.  Unlike _s_e_t_b_u_f and
     _s_e_t_b_u_f_f_e_r it can be used at any time that the file



Printed 12/27/86          May 12, 1986                          1






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



     descriptor is active.

     A file can be changed from unbuffered or line buffered to
     block buffered by using _f_r_e_o_p_e_n (see _f_o_p_e_n(3S)).  A file can
     be changed from block buffered or line buffered to unbuf-
     fered by using _f_r_e_o_p_e_n followed by _s_e_t_b_u_f with a buffer
     argument of NULL.

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

BUGS
     The standard error stream should be line buffered by
     default.

     The _s_e_t_b_u_f_f_e_r and _s_e_t_l_i_n_e_b_u_f functions are not portable to
     non-4.2BSD versions of UNIX.  On 4.2BSD and 4.3BSD systems,
     _s_e_t_b_u_f always uses a suboptimal buffer size and should be
     avoided.  _S_e_t_b_u_f_f_e_r is not usually needed as the default
     file I/O buffer sizes are optimal.


































Printed 12/27/86          May 12, 1986                          2