Storing Instance-Specific Information

It is sometimes necessary for a driver to save instance-specific information. Two functions supplied by winmm.dll, mciSetDriverData and mciGetDriverData, are useful for associating instance-specific information with driver ID’s. You can use these functions to store and retrieve a longword for each assigned driver ID (that is, for each opened device or element). Drivers typically cast the longword to a pointer to a locally allocated structure.