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mmioAdvance function

The mmioAdvance function advances the I/O buffer of a file set up for direct I/O buffer access with the mmioGetInfo function.


MMRESULT mmioAdvance(
   HMMIO      hmmio,
   LPMMIOINFO lpmmioinfo,
   UINT       wFlags



File handle of a file opened by using the mmioOpen function.


Pointer to the MMIOINFO structure obtained by using the mmioGetInfo function. This structure is used to set the current file information, and then it is updated after the buffer is advanced. This parameter is optional.


Flags for the operation. It can be one of the following.

Value Meaning
MMIO_READBuffer is filled from the file.
MMIO_WRITEBuffer is written to the file.


Return value

Returns MMSYSERR_NOERROR if successful or an error otherwise. Possible error values include the following.

Return codeDescription

The specified memory file cannot be expanded, probably because the adwInfo member of the MMIOINFO structure was set to zero in the initial call to the mmioOpen function.


An error occurred while refilling the buffer.


The contents of the buffer could not be written to disk.


There was not enough memory to expand a memory file for further writing.


The specified file is not opened for buffered I/O.



If the file is opened for reading, the I/O buffer is filled from the disk. If the file is opened for writing and the MMIO_DIRTY flag is set in the dwFlags member of the MMIOINFO structure, the buffer is written to disk. The pchNext,pchEndRead, and pchEndWrite members of the MMIOINFO structure are updated to reflect the new state of the I/O buffer.

If the specified file is opened for writing or for both reading and writing, the I/O buffer is flushed to disk before the next buffer is read. If the I/O buffer cannot be written to disk because the disk is full, mmioAdvance returns MMIOERR_CANNOTWRITE.

If the specified file is open only for writing, the MMIO_WRITE flag must be specified.

If you have written to the I/O buffer, you must set the MMIO_DIRTY flag in the dwFlags member of the MMIOINFO structure before calling mmioAdvance. Otherwise, the buffer will not be written to disk.

If the end of file is reached, mmioAdvance still returns successfully even though no more data can be read. To check for the end of the file, check if the pchNext and pchEndRead members of the MMIOINFO structure are equal after calling mmioAdvance.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]


Mmsystem.h (include Windows.h)







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