SETBUF(3S)                                                          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.  Normally 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 termi‐
       nal it  is  line  buffered.   The  standard  stream  stderr  is  always
       unbuffered.

       _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 constant pointer NULL, input/output
       will be completely unbuffered.  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 automati‐
       cally  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 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 unbuffered 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.



4th Berkeley Distribution        May 12, 1986                       SETBUF(3S)