How to convert a short path in a long one

//declaration
function GetLongPathName(lpszShortPath: PChar; lpszLongPath: PChar;
  cchBuffer: DWORD): DWORD; stdcall;

  //implementation
  function GetLongPathName; external kernel32 Name 'GetLongPathNameA';

// -----------------------------------------------------------------------------

function WinAPI_GetLongPathName(const ShortName: string): string;
begin
  SetLength(Result, MAX_PATH);
  SetLength(Result, GetLongPathName(PChar(ShortName), PChar(Result), MAX_PATH));
end;