????\u003F\u003F (C99)\U00003F\U00003F (C99)\?\?\x3F\x3F (encoding-dependent)\077\077 (encoding-dependent)\u{3F}\u{3F} (C++23)\x{3F}\x{3F} (C++23, encoding-dependent)\o{077}\o{077} (C++23, encoding-dependent)\?\?\U0000003F\U0000003F\u003F\u003F\x3F\x3F (encoding-dependent)\077\077 (encoding-dependent)\u003F\u003F\u{3F}\u{3F}\u003F\u003F\x3F\x3F\3F\3F\00003F\00003F=3F=3F%3F%3F