BCGSuite for MFC
BCGCBPRODLLEXPORT UINT BCGM_CALENDAR_ON_MONTHCHANGED

This message is sent to owner of calendar bar control when selected month has been changed.

Parameters
wParamThis parameter is not used.
lParama handle to calendar bar control.
Returns
The return value is ignored.

You should process this message to receive notifications from CBCGPCalendarBar objects when selection (selected month) has been changed.