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FFLUSH(3) FreeBSD Library Functions Manual FFLUSH(3) NAME fflush, fpurge - flush a stream SYNOPSIS #include <stdio.h> int fflush(FILE *stream); int fpurge(FILE *stream); DESCRIPTION The function fflush() forces a write of all buffered data for the given output or update stream via the stream's underlying write function. If stream is a stream opened for reading with fdopen(3), fopen(3), or freopen(3) of a seekable file and it is not already at EOF then fflush() sets the seek position of the file to the file position of the stream and discards any text pushed back via ungetc(3) or ungetwc(3). The open status of the stream is unaffected. If the stream argument is NULL, fflush() flushes all open output streams. The function fpurge() erases any input or output buffered in the given stream. For output streams this discards any unwritten output. For input streams this discards any input read from the underlying object but not yet obtained via getc(3); this includes any text pushed back via ungetc(3). RETURN VALUES Upon successful completion 0 is returned. Otherwise, EOF is returned and the global variable errno is set to indicate the error. ERRORS [EBADF] stream is not an open stream or, in the case of fflush(), not a stream open for writing. The function fflush() may also fail and set errno for any of the errors specified for the routine write(2). SEE ALSO write(2), fclose(3), fopen(3), setvbuf(3) STANDARDS The fflush() function conforms to ANSI X3.159-1989 ("ANSI C89"). HISTORY A predecessor flush() first appeared in Version 1 AT&T UNIX. The fflush() function first appeared in Version 4 AT&T UNIX. FreeBSD 14.1-RELEASE-p8 August 30, 2024 FreeBSD 14.1-RELEASE-p8