[This is preliminary documentation and subject to change.]
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 total number of items for which memory has been pre-allocated, that is, the total number of items added by all successful CB_INITSTORAGE messages.
If the message fails, the return value is CB_ERRSPACE.
Windows NT: For Windows NT version 4.0, this message does not allocate the specified amount of memory; however, it always returns the value specified in the cItems parameter. For Windows NT version 5.0, the message allocates memory and returns the success and error values described above.
The CB_INITSTORAGE 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: Requires version 5.0 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, CB_ADDSTRING, CB_DIR, CB_INSERTSTRING