Implementation status: partially implemented


#include <stdio.h>

int fflush(FILE *stream);


Flushes the output buffer of a stream.


stream - the stream to be flushed

If stream points to an output stream, any unwritten data for that stream is written to the file, and the last data modification and last file status change timestamps of the underlying file are marked for update.

If stream points to an input stream, with an underlying file description, if the file is not already at EOF, and the file is one capable of seeking, the file offset of the underlying open file description is set to the file position of the stream, and any characters pushed back onto the stream by ungetc() or ungetwc() that have not subsequently been read from the stream are discarded (without further changing the file offset).

If stream is a null pointer, fflush() performs this flushing action on all streams for which the behavior is defined above.

Return value

On success fflush() returns 0; otherwise, it sets the error indicator for the stream and returns EOF, and sets errno to indicate the error.


[EAGAIN] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the write operation.
[EBADF] The file descriptor underlying stream is not valid.
[EFBIG] An attempt was made to write a file that exceeds the maximum file size.
[EFBIG] An attempt was made to write a file that exceeds the file size limit of the process.
[EFBIG] The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.
[EINTR] The fflush() function was interrupted by a signal.
[EIO] The process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the calling thread is not blocking SIGTTOU, the process is not ignoring SIGTTOU, and the process group of the process is orphaned.
[ENOMEM] The underlying stream was created by open_memstream() or open_wmemstream() and insufficient memory is available.
[ENOSPC] There was no free space remaining on the device containing the file or in the buffer used by the fmemopen() function.
[EPIPE] An attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal is also sent to the thread.
[ENXIO] A request was made of a nonexistent device, or the request was outside the capabilities of the device

Implementation tasks

  • Implement error handling as described above.