fflush(3)

NAME

   fflush - flush a stream

SYNOPSIS

   #include <stdio.h>

   int fflush(FILE *stream);

DESCRIPTION

   For  output streams, fflush() forces a write of all user-space buffered
   data for the given output or update stream via the stream's  underlying
   write function.

   For input streams associated with seekable files (e.g., disk files, but
   not pipes or terminals), fflush() discards any buffered data  that  has
   been fetched from the underlying file, but has not been consumed by the
   application.

   The open status of the stream is unaffected.

   If the stream argument  is  NULL,  fflush()  flushes  all  open  output
   streams.

   For a nonlocking counterpart, see unlocked_stdio(3).

RETURN VALUE

   Upon  successful  completion 0 is returned.  Otherwise, EOF is returned
   and errno is set to indicate the error.

ERRORS

   EBADF  stream is not an open stream, or is not open for writing.

   The function fflush() may also fail and set errno for any of the errors
   specified for write(2).

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface  Attribute      Value   
   
   fflush()   Thread safety  MT-Safe 
   

CONFORMING TO

   C89, C99, POSIX.1-2001, POSIX.1-2008.

   POSIX.1-2001 did  not  specify  the  behavior  for  flushing  of  input
   streams, but the behavior is specified in POSIX.1-2008.

NOTES

   Note  that fflush() flushes only the user-space buffers provided by the
   C library.  To ensure that the data is physically stored  on  disk  the
   kernel  buffers  must  be  flushed  too,  for  example, with sync(2) or
   fsync(2).

SEE ALSO

   fsync(2), sync(2), write(2), fclose(3), fileno(3), fopen(3), setbuf(3),
   unlocked_stdio(3)

COLOPHON

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

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