FFLUSH(3) | 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) or ungetwc(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.

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.

# HISTORY

A predecessor `flush`() first appeared in Version 1 AT&T UNIX. The `fflush`() function first appeared in Version 4 AT&T UNIX. The `fpurge`() function first appeared in 4.3BSD-Reno.

June 12, 2025 | Debian