5 Lexical conventions [lex]

5.4 Comments [lex.comment]

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.
[Note 1: 
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]