fflush(3) — Linux manual page


fflush(3)               Library Functions Manual               fflush(3)

NAME         top

       fflush - flush a stream

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <stdio.h>

       int fflush(FILE *_Nullable stream);

DESCRIPTION         top

       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

       For a nonlocking counterpart, see unlocked_stdio(3).

RETURN VALUE         top

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

ERRORS         top

       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         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ fflush()                            │ Thread safety │ MT-Safe │

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       C89, 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         top

       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         top

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

Linux man-pages (unreleased)     (date)                        fflush(3)

Pages that refer to this page: fsync(2)fclose(3)fcloseall(3)fmemopen(3)fopen(3)fpurge(3)fseek(3)open_memstream(3)popen(3)setbuf(3)stdin(3)stdio(3)xdr(3)