NAME

       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations

SYNOPSIS

       #include <stdio.h>

       void setbuf(FILE *stream, char *buf);
       void setbuffer(FILE *stream, char *buf, size_tsize);
       void setlinebuf(FILE *stream);
       int setvbuf(FILE *stream, char *buf, int mode , 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 output or input is read from any stream attached to a terminal
       device (typically stdin).  The function fflush(3) may be  used  to  force  the  block  out  early.   (See
       fclose(3).)   Normally  all  files  are  block  buffered.  When the first I/O operation occurs on a file,
       malloc(3) is called, and a buffer is obtained.  If a stream refers to  a  terminal  (as  stdout  normally
       does) it is line buffered.  The standard error stream stderr is always unbuffered by default.

       The setvbuf function may be used at any time on any open stream to change its buffer.  The mode parameter
       must be one of the following three macros:

              _IONBF unbuffered

              _IOLBF line buffered

              _IOFBF fully buffered

       Except  for  unbuffered  files,  the buf argument should point to a buffer at least size bytes long; this
       buffer will be used instead of the current buffer.  If the  argument  buf  is  NULL,  only  the  mode  is
       affected;  a  new buffer will be allocated on the next read or write operation.  The setvbuf function may
       be used at any time, but can only change the mode of a stream when it is not ``active'': that is,  before
       any I/O, or immediately after a call to fflush.

       The  other  three  calls  are,  in  effect,  simply aliases for calls to setvbuf.  The setbuf function is
       exactly equivalent to the call

              setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);

       The setbuffer function is the same, except that the size of the buffer is up to the caller,  rather  than
       being determined by the default BUFSIZ.  The setlinebuf function is exactly equivalent to the call:

              setvbuf(stream, (char *)NULL, _IOLBF, 0);

CONFORMING TO

       The setbuf and setvbuf functions conform to ANSI X3.159-1989 (``ANSI C'').

BUGS

       The  setbuffer and setlinebuf functions are not portable to versions of BSD before 4.2BSD, and may not be
       available under Linux.  On 4.2BSD and 4.3BSD systems, setbuf always uses a  suboptimal  buffer  size  and
       should be avoided.

       You  must  make  sure  that both buf and the space it points to still exist by the time stream is closed,
       which also happens at program termination.

       For example, the following is illegal:

       #include <stdio.h>
       int main()
       {
           char buf[BUFSIZ];
           setbuf(stdin, buf);
           printf("Hello, world!\n");
           return 0;
       }

SEE ALSO

       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

BSD MANPAGE                                     29 November 1993                                       SETBUF(3)