5 Lexical conventions [lex]

5.9 Preprocessing numbers [lex.ppnumber]

. digit
pp-number digit
pp-number identifier-nondigit
pp-number ' digit
pp-number ' nondigit
pp-number e sign
pp-number E sign
pp-number p sign
pp-number P sign
pp-number .
Preprocessing number tokens lexically include all integer-literal tokens ([lex.icon]) and all floating-point-literal tokens ([lex.fcon]).
A preprocessing number does not have a type or a value; it acquires both after a successful conversion to an integer-literal token or a floating-point-literal token.