---
name: "fflush"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/fflush"
---

# fflush(3)

flush a stream

## NAME

**fflush**, **fpurge** – flush a stream

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<stdio.h\>**

*int*\

**fflush**(*FILE \*stream*);

*int*\

**fpurge**(*FILE \*stream*);

## DESCRIPTION

The function **fflush**() synchronizes the state of the given *stream* in light of buffered I/O. For output or update streams it writes all buffered data via the stream's underlying write function. For input streams it seeks to the current file position indicator via the stream's underlying seek function. The open status of the stream is unaffected.

If the *stream* argument is NULL, **fflush**() flushes *all* open 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)](/getc/3.md); this includes any text pushed back via [ungetc(3)](/ungetc/3.md).

## RETURN VALUES

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

## ERRORS

- \[EBADF\]

  The *stream* argument is not an open stream.

The function **fflush**() may also fail and set *errno* for any of the errors specified for the routines [write(2)](/write/2.md) and [lseek(2)](/lseek/2.md).

## SEE ALSO

[write(2)](/write/2.md), [fclose(3)](/fclose/3.md), [fopen(3)](/fopen/3.md), [lseek(2)](/lseek/2.md), [setbuf(3)](/setbuf/3.md)

## STANDARDS

The **fflush**() function conforms to ISO/IEC 9899:1990 (“ISO C90”) and Version 3 of the Single UNIX Specification (“SUSv3”).