TStringList oddity

RTL
1

I’ve been using Delphi since 1995, so I’ve used TStringList a few thousand times over the years. You would think that means I know it inside out - but today I discovered this gem while trying to figure out how items were magically disappearing

procedure TStrings.SetValueFromIndex(Index: Integer; const Value: string);
begin
  if Value <> '' then
  begin
    if Index < 0 then Index := Add('');
    Put(Index, Names[Index] + NameValueSeparator + Value);
  end
  else
    if Index >= 0 then Delete(Index); //<<<< WTF???
end;

So it seems you cannot use .ValueFromIndex to set a value to an empty string as it Deletes the item.

I’m struggling to figure the mindset of whoever decided that was a good idea :roll_eyes:

I’ve probably encountered this issue before and forgotten about it… posting here so I get a search result next time I search for ValueFromIndex :smirk:

1 Like
2

Yep, been there, saw that, have bitemarks :wink:

Alex

``

So it seems you cannot use .ValueFromIndex to set a value to an empty string as it Deletes the item.

3

Why would you not use
Strings[index]:=’’;
or as it is the default
MyStringList[Index]:=’’;

Using SetValueFromIndex risks breaking a sorted list as it is not virtual.

4

Because I’m using it for Name=Value pairs

String.ValueFromIndex[index] := 'foo';

sets the value without changing tne name.

5

And the Put in the implementation does any sorted required,
Sorry

6

IIRC, the ‘mindset’ was to imitate Win32 .ini routines, which delete entries (and even whole sections!) by setting the value to an empty string. See WritePrivateProfileStringA function (winbase.h) - Win32 apps | Microsoft Docs.