Using Inno Setup LoadStringFromFile always gives "Type mismatch"

Question

I am trying to read a simple text file, but whenever I use the function LoadStringFromFile it always gives me

Type mismatch.

The text file that I am trying to read from contains a file path to a folder in User Documents. Something like c:\users\username\document\foldername\.

I know that Inno Setup has a directory constant for User Document, but the users don't have rights to install. When running the installer with admin account the directory constant would give a different file path. This text file has the real file path that I want to use for the installation.

function getPath(Param: String) : String;
  var line: AnsiString;
begin
    Result := LoadStringFromFile(ExpandConstant('{commonpf64}\appfolder\sometextfile.txt'), line);
end;

Answer 1

The LoadStringFromFile function returns Boolean value indicating success of the read. The actual contents is returned in the S argument (or line in your code).

Your function might look like:

function getPath(Param: String): String;
var
  Path: string;
  Line: AnsiString;
begin
  Path := ExpandConstant('{commonpf64}\appfolder\sometextfile.txt');
  if LoadStringFromFile(Path, Line) then
  begin
    Result := Trim(Line); // Converts from AnsiString to string on the way
  end
    else
  begin
    RaiseException(Format('Error reading %s', [Path]));
  end;
end;