The COMPAREITEMSTRUCT structure supplies the identifiers and application-supplied data for two items in a sorted owner-draw combo box or list box.
Whenever an application adds a new item to an owner-draw combo or list box created with the CBS_SORT or LBS_SORT style, Windows sends the owner a WM_COMPAREITEM message. The lParam parameter of the message contains a long pointer to a COMPARE-ITEMSTRUCT data structure. When the owner receives the message, the owner compares the two items and returns a value indicating which item sorts before the other. For more information, see the description of the WM_COMPAREITEM message in Chapter 6, “Messages Directory.”
typedef struct tagCOMPAREITEMSTRUCT {
WORD CtlType;
WORD CtlID;
HWND hwndItem;
WORD itemID1;
DWORD itemData1;
WORD itemID2;
DWORD itemData2;
} COMPAREITEMSTRUCT;
The COMPAREITEMSTRUCT structure has the following fields:
| Field | Description | |
| CtlType | Is ODT_LISTBOX (which specifies an owner-draw list box) or ODT_COMBOBOX (which specifies an owner-draw combo box). | |
| CtlID | Is the control ID for the list box or combo box. | |
| hwndItem | Is the window handle of the control. | |
| itemID1 | Is the index of the first item in the list box or combo box being compared. | |
| itemData1 | Is application-supplied data for the first item being compared. This value was passed as the lParam parameter of the message that added the item to the combo or list box. | |
| Field | Description | |
| itemID2 | Is the index of the second item in the list box or combo box being compared. | |
| itemData2 | Is application-supplied data for the second item being compared. This value was passed as the lParam parameter of the message that added the item to the combo or list box. |