# setbuf(3)

    NAME
         setbuf, setvbuf - assign buffering to a stream

    SYNOPSIS
         #include <stdio.h>

         int setbuf(FILE *stream, char *buf)
         int setvbuf(FILE *stream, char *buf, int type, size_t 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(3)) 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(3) on the file.  If the standard stream stdout refers to a  terminal
         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];

         Setvbuf, an alternate form of setbuf, is used after  a  stream  has  been
         opened but before it is read or written.  It has three uses, depending on
         the value of the type argument:

         setvbuf(stream, buf, _IOFBF, size)
              Causes input/output to be fully buffered using the  character  array
              buf  whose  size  is determined by the size argument.  If buf is the
              constant pointer NULL, then an automatically allocated  buffer  will
              be used.

         setvbuf(stream, buf, _IOLBF, size)
              Like above, except that output  will  be  line  buffered,  i.e.  the
              buffer  will  be  flushed  when  a newline is written, the buffer is
              full, or input is requested.

         setvbuf(stream, buf, _IONBF, size)
              Causes input/output to be completely unbuffered.  Buf and  size  are
              ignored.

         A file can  be  changed  between  unbuffered,  line  buffered,  or  block
         buffered  by  using  freopen  (see  fopen(3)) followed by the appropriate
         setvbuf call.

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