Windows sends the WM_COMPAREITEM message to determine the relative position of a new item in the sorted list of an owner-drawn combo box or list box. Whenever the application adds a new item, Windows sends this message to the owner of a combo box or list box created with the CBS_SORT or LBS_SORT style.
WM_COMPAREITEM
idCtl = wParam; // control identifier
lpcis = (LPCOMPAREITEMSTRUCT) lParam; // structure with items
Parameters
idCtl
Value of wParam. Specifies the identifier of the control that sent the WM_COMPAREITEM message.
lpcis
Value of lParam. Points to a COMPAREITEMSTRUCT structure that contains the identifiers and application-supplied data for two items in the combo or list box.
Return Values
The return value indicates the relative position of the two items. It may be any of the following:
| Value | Meaning |
| -1 | Item 1 precedes item 2 in the sorted order. |
| 0 | Items 1 and 2 are equivalent in the sorted order. |
| 1 | Item 1 follows item 2 in the sorted order. |
Remarks
When the owner of an owner-drawn combo box or list box receives this message, the owner returns a value indicating which of the items specified by the COMPAREITEMSTRUCT structure will appear before the other. Typically, Windows sends this message several times until it determines the exact position for the new item.
See Also