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_t size);

       void setlinebuf(FILE *stream);

       int setvbuf(FILE *stream, char *buf, int mode, size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setbuffer(), setlinebuf(): _BSD_SOURCE

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 on any open stream to change its buffer.  The mode argument 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 only after opening a stream and before any other operations have been performed on it.

       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, NULL, _IOLBF, 0);

RETURN VALUE

       The  function  setvbuf()  returns  0  on  success.  It returns nonzero on failure (mode is invalid or the
       request cannot be honored).  It may set errno on failure.

       The other functions do not return a value.

CONFORMING TO

       The setbuf() and setvbuf() functions conform to C89 and C99.

BUGS

       The setbuffer() and setlinebuf() functions are not portable to versions of BSD  before  4.2BSD,  and  are
       available under Linux since libc 4.5.21.  On 4.2BSD and 4.3BSD systems, setbuf() always uses a suboptimal
       buffer size and should be avoided.

       You  must  make  sure  that the space that buf points to still exists by the time stream is closed, which
       also happens at program termination.  For example, the following is invalid:

       #include <stdio.h>

       int
       main(void)
       {
           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)

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux                                              2012-08-03                                          SETBUF(3)