Question

I wrote this function wich compares string and return TRUE if it matches and FALSE if it doesn’t.

The only problem is that when I compile, I get an error saying that the result can be undefined. I know this is not a problem as there are only 2 possible outcome in this particular situation but I’m kind of a perfectionnist and I want to get better.
Can any of you enlighten me?

function filterUPC(upc: String): Boolean; 
var
  i, pos1: integer;
  Plano: TStringList;
  upcPlano: String;
begin
  Plano := TStringList.Create;
  if (fmMain.lblPlanook.Visible) and 
     not (fmMain.lblPlanook.Caption = 'INCOMPATIBLE') then
  begin
    Plano.LoadFromFile(fmMain.ebPlano.Text);
    for i := 0 to Plano.Count - 1 do
    begin
      pos1:=AnsiPos(';', Plano[i]);
      upcPlano := AnsiMidStr(Plano[i], pos1 + 1, 12);
      if (upc = upcPlano) then
      begin
        Result := TRUE;
        Break;
      end
      else if (i = Plano.Count - 1) then
      begin
        Result := FALSE;
      end;
    end;
  end
  else
  begin
    Result := FALSE;
  end;
  Plano.Free;
end;

Answer 1

Your result is undefined if Plano is empty. In that case, the for-loop never executes and Result is never set.

Also, you should really wrap the TStringList create/free in a try/finally (since you’re a perfectionist 😉

Here’s what I would do:

function filterUPC(upc: String): Boolean;
var
  i, pos1: integer;
  Plano: TStringList;
  upcPlano: String;
begin
  Result := FALSE;
  Plano := TStringList.Create;
  try
    if (fmMain.lblPlanook.Visible) and (fmMain.lblPlanook.Caption <> 'INCOMPATIBLE') then
    begin
      Plano.LoadFromFile(fmMain.ebPlano.Text);
      for i := 0 to Plano.Count -1 do
      begin
        pos1 := AnsiPos(';', Plano[i]);
        upcPlano := AnsiMidStr(Plano[i], pos1 + 1, 12);
        if (upc = upcPlano) then
        begin
          Result := TRUE;
          Break;
        end;
      end;
    end
  finally
    Plano.Free;
  end;
end;

I’ve added Result:=FALSE; to the top, and removed the else checks. The try/finally guarantees that Plano will be freed, even if an exception is raised.