Author: Tomas Rutkauskas

I want to copy selected items (only text) from a TListBox that has LBS_EXTENDEDSEL 
style to the standard clipboard using only API functions.

Answer:

This code is untested and requires the unit APIClipboard from Tip "Clipboard access 
routines which use only API functions".
1   
2   procedure CopySelectedListboxItemsToClipboard(listboxwnd: HWND);
3   
4     function GetItem(num: Integer): string;
5     begin
6       SetLength(Result, SendMessage(listboxwnd, LB_GETTEXTLEN, num, 0));
7       if Length(Result) > 0 then
8         SendMessage(listboxwnd, LB_GETTEXT, num, LPARAM(@Result[1]));
9     end;
10  
11  var
12    num: Integer;
13    selIndices: array of Integer;
14    sl: TStringlist;
15    S: string;
16  begin
17    num = SendMessage(listboxwnd, LB_GETSELCOUNT, 0, 0);
18    if num = LB_ERR then
19    begin
20      {listbox is a single selection listbox}
21      num := SendMessage(listboxwnd, LB_GETCURSEL, 0, 0);
22      if num = LB_ERR then
23        Exit; {no selected item}
24      S := GetItem(num);
25    end
26    else
27    begin
28      SetLength(selIndices, num);
29      SendMessage(listboxwnd, LB_GETSELITEMS, num, LPARAM(@selIndices[0]));
30      sl := TStringlist.Create;
31      try
32        for num := 0 to High(selIndices) do
33          sl.Add(GetItem(selIndices[num]));
34        S := sl.Text;
35      finally
36        sl.free;
37      end;
38    end;
39    StringToClipboard(S);
40  end;