An application sends a ZGM_GETREGDATEMONTH message to get the month of the date in the internal date register.
ZGM_GETREGDATEMONTH
wParam = 0; //not used; must be 0
lParam = 0; //not used; must be 0
If the date in the internal date register is valid, this message returns the month of that date. Otherwise, the message returns 0.