The TVM_GETISEARCHSTRING message retrieves the incremental search string for a tree-view control. The tree-view control uses the incremental search string to select an item based on characters typed by the user. You can send this message explicitly or by using the TreeView_GetISearchString macro.
TVM_GETISEARCHSTRING wParam = 0; lParam = (LPARAM) (LPSTR) lpsz;
Returns the number of characters in the incremental search string.
If the tree-view control is not in incremental search mode, the return value is zero.