fflush - flush a stream
int fflush(FILE *
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.
stream argument is NULL, fflush() flushes
all open output streams.
For a nonlocking counterpart, see unlocked_stdio(3).
Upon successful completion 0 is returned. Otherwise, EOF is returned and
errno is set to indicate the error.
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.
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