setbuf(3S-BSD)    MISC. REFERENCE MANUAL PAGES     setbuf(3S-BSD)



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

SYNOPSIS
     cc [ flag... ] file ... -lucb
     #include <stdio.h>
     setbuf(stream, buf)
     FILE *stream;
     char *buf;
     setbuffer(stream, buf, size)
     FILE *stream;
     char *buf;
     int size;
     setlinebuf(stream)
     FILE *stream;
     int setvbuf(stream, buf, type, size)
     FILE *stream;
     char *buf;
     int type, 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
     encountered or  input  is  read  from  stdin.   fflush  (see
     fclose(3S))  may be used to force the block out early.  Nor-
     mally all files are block buffered.  A  buffer  is  obtained
     from malloc(3C) upon the first getc or putc(3S) on the file.
     If the standard stream stdout refers to  a  terminal  it  is
     line  buffered.  The standard stream stderr is unbuffered by
     default.  setbuf can be used after a stream has been  opened
     but  before  it  is  read  or  written.  It causes the array
     pointed to by buf to be used  instead  of  an  automatically
     allocated  buffer.  If buf is the NULL pointer, input/output
     will be completely unbuffered.  A manifest constant  BUFSIZ,
     defined in the <stdio.h> header file, tells how big an array
     is needed:

          char buf[BUFSIZ]; setbuffer, an alternate form of  set-
          buf,  can  be  used  after a stream has been opened but
          before it is read or written.  It  uses  the  character
          array buf whose size is determined by the size argument
          instead of an automatically allocated buffer.   If  buf
          is  the  NULL  pointer, input/output will be completely
          unbuffered.  setvbuf can be used  after  a  stream  has
          been  opened  but  before  it is read or written.  type
          determines how stream will be buffered.   Legal  values
          for type (defined in <stdio.h>) are:



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setbuf(3S-BSD)    MISC. REFERENCE MANUAL PAGES     setbuf(3S-BSD)



         IOFBF
             fully buffers the input/output.

         IOLBF
             line buffers the output; the buffer will be  flushed
             when  a  NEWLINE  is written, the buffer is full, or
             input is requested.

         IONBF
             completely unbuffers the input/output.   If  buf  is
             not the NULL pointer, the array it points to will be
             used for  buffering,  instead  of  an  automatically
             allocated  buffer.   size  specifies the size of the
             buffer to be used.  setlinebuf is used to change the
             buffering  on a stream from block buffered or unbuf-
             fered to line buffered.  Unlike  setbuf,  setbuffer,
             and  setvbuf,  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 freopen (see fopen(3S)).   A  file  can  be
             changed  from  block  buffered  or  line buffered to
             unbuffered by using freopen followed by setbuf  with
             a buffer argument of NULL.

NOTE
     A common source of error is allocating buffer  space  as  an
     ``automatic''  variable in a code block, and then failing to
     close the stream in the same block.

SEE ALSO
     fclose(3S),  fopen(3S),  fread(3S),  getc(3S),   malloc(3C),
     printf(3S),    putc(3S),   puts(3S),   setbuf(3S)   in   the
     Programmer's Reference Manual.

RETURN VALUE
     If an illegal value for type or size  is  provided,  setvbuf
     returns  a  non-zero  value.   Otherwise, the value returned
     will be zero.

















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