fflush

FFLUSH(3)                  Linux Programmer's Manual                 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 5.01 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/.



GNU                               2017-09-15                         FFLUSH(3)