An application sends a ZGM_GETREGDATEDOY message to get the day of the year of the date in the internal date register.
ZGM_GETREGDATEDOY
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 day of the year of that date. Otherwise, the message returns 0.
If the date is valid, return value will be in the range of [1..366].