How to use placeholder like {app} or {temp} in Inno Setup script?

Question

How can I access (directory) constants from Inno Setup script code ?

I have tried the following without success:

Answer 1

Use the ExpandConstant function to expand any of the constants value:

function dbExistis: Boolean;
begin
  Result := FileExists(ExpandConstant('{commonappdata}\LR-International\DB_LR.IB'));
end;

Answer 2

Use ExpandConstant function

function dbExistis() : Boolean;
  begin
    Result := FileExists(ExpandConstant('{commonappdata}') + '\LR-International\DB_LR.IB');
  end;