An application sends the CB_INITSTORAGE message before adding a large number of items to the list box portion of a combo box. This message allocates memory for storing list box items.
CB_INITSTORAGE wParam = (WPARAM) (int) cItems; // number of items to add lParam = (LPARAM) (DWORD) cb; // amount of memory to allocate, in bytes
If the message is successful, the return value is the maximum number of items that the memory object can store.
If the message fails, the return value is CB_ERR.
Windows 95: This message helps speed up the initialization of combo boxes that have a large number of items (over 100). It reserves the specified amount of memory so that subsequent CB_ADDSTRING, CB_INSERTSTRING, and CB_DIR messages take the shortest possible time. You can use estimates for the cItems and cb parameters. If you overestimate, the extra memory is allocated, if you underestimate, the normal allocation is used for items that exceed the requested amount.
Windows NT: This message is not needed on Windows NT. It does not reserve the specified amount of memory, because available memory is virtually unlimited. The return value is always the value specified in the cItems parameter.
CB_ADDSTRING, CB_DIR, CB_INSERTSTRING