If the hmmio parameter represents a file that was opened using mmioOpen, and hmmio parameter is currently set up for buffered I/O, and the buffer has been written into (by mmioWrite, or by direct caller access to the buffer using mmioGetInfo) since the last time the buffer was flushed to disk, mmioFlush writes the buffer to the disk.

If the hmmio parameter is a memory file or is unbuffered, this function returns the appropriate error message indicated. Note that mmioFlush might fail if there is insufficient disk space to write the buffer, even if the preceding mmioWrite functions succeeded.