NAME

       fflush - flush a stream

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdio.h>

       int fflush(FILE *_Nullable 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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       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

       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),  fpurge(3),  setbuf(3),
       unlocked_stdio(3)