fflush

       #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),   fopen(3),    setbuf(3),
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