mmioGetInfo function (mmiscapi.h)

The mmioGetInfo function retrieves information about a file opened by using the mmioOpen function. This information allows the application to directly access the I/O buffer, if the file is opened for buffered I/O.


MMRESULT mmioGetInfo(
  HMMIO      hmmio,
  LPMMIOINFO pmmioinfo,
  UINT       fuInfo



File handle of the file.


Pointer to a buffer that receives an MMIOINFO structure that mmioGetInfo fills with information about the file.


Reserved; must be zero.

Return value

Returns zero if successful or an error otherwise.


To directly access the I/O buffer of a file opened for buffered I/O, use the following members of the MMIOINFO structure filled by mmioGetInfo:

  • The pchNext member points to the next byte in the buffer that can be read or written. When you read or write, increment pchNext by the number of bytes read or written.
  • The pchEndRead member points to 1 byte past the last valid byte in the buffer that can be read.
  • The pchEndWrite member points to 1 byte past the last location in the buffer that can be written.
After you read or write to the buffer and modify pchNext, do not call any multimedia file I/O functions except mmioAdvance until you call the mmioSetInfo function. Call mmioSetInfo when you are finished directly accessing the buffer.

When you reach the end of the buffer specified by the pchEndRead or pchEndWrite member, call mmioAdvance to fill the buffer from the disk or write the buffer to the disk. The mmioAdvance function updates the pchNext, pchEndRead, and pchEndWrite members in the MMIOINFO structure for the file.

Before calling mmioAdvance or mmioSetInfo to flush a buffer to disk, set the MMIO_DIRTY flag in the dwFlags member of the MMIOINFO structure for the file. Otherwise, the buffer will not be written to disk.

Do not decrement pchNext or modify any members in the MMIOINFO structure other than pchNext and dwFlags. Do not set any flags in dwFlags except MMIO_DIRTY.


Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header mmiscapi.h (include Mmiscapi.h, Windows.h)
Library Winmm.lib
DLL Winmm.dll