Use the mmioCFSetInfo function to modify information that is stored in the CTOC header of an open RIFF compound file. You should only modify the aulExHdrFldUsage and aulExHdrField fields.
The mmioCFSetInfo function requires a pmmcfinfo parameter which identifies a pointer to a user-supplied buffer that contains the modified CTOC header. This buffer was filled in by mmioCFGetInfo and then modified by the user. Use the cBytes parameter to specify the size of the pmmcfinfo buffer. This is the maximum number of bytes that will be copied.