The system 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, the system 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
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. |
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, the system sends this message several times until it determines the exact position for the new item.
If a dialog box procedure handles this message, it should cast the desired return value to a BOOL and return the value directly. The DWL_MSGRESULT value set by the SetWindowLong function is ignored.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Combo Boxes Overview, Combo Box Messages, COMPAREITEMSTRUCT