Como utilizar os dados do usuario que esta logado?

Function Read_userid: string;
var
LPTSTR: array[0..100] of char; // address of name buffer
LPDWORD: dword; // address of size of name buffer
begin
LPTSTR := ´´;
LPDWORD := 100;
getusername(LPTSTR, LPDWORD);
read_userid := trim(LPTSTR);
end;