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/.