4.3BSD - /usr/man/cat3/setbuffer.0

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.  Fflush (see  fclose(3S))  may
       be  used  to  force  the block out early.  Normally all files are block
       buffered.  A buffer is obtained from malloc(3) upon the first  getc  or
       putc(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.

       Setbuf  is used after a stream has been opened but before it is read or
       written.  The character array buf is used instead of  an  automatically
       allocated  buffer.   If  buf 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];

       Setbuffer, an alternate form of setbuf, is used after a stream has been
       opened but before it is read or written.  The character array buf whose
       size is determined by the size argument is used instead of an automati‐
       cally  allocated  buffer.   If  buf  is  the  constant  pointer   NULL,
       input/output will be completely unbuffered.

       Setlinebuf  is  used  to change stdout or stderr from block buffered or
       unbuffered to line buffered.  Unlike setbuf and  setbuffer  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.

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


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