5 Lexical conventions [lex]

5.7 Comments [lex.comment]

1
#
The characters /* start a comment, which terminates with the characters */.
These comments do not nest.
The characters // start a comment, which terminates immediately before the next new-line character.
If there is a form-feed or a vertical-tab character in such a comment, only white-space characters shall appear between it and the new-line that terminates the comment; no diagnostic is required.
[Note
:
The comment characters //, /*, and */ have no special meaning within a // comment and are treated just like other characters.
Similarly, the comment characters // and /* have no special meaning within a /* comment.
— end note
]