From the C++ Standard
2.4 Trigraph sequences [lex.trigraph]
1 Before any other processing takes place, each occurrence of one of the following sequences of three characters (“trigraph sequences”) is replaced by the single character indicated in Table 1.
Table 1 — Trigraph sequences Trigraph Replacement Trigraph Replacement Trigraph Replacement
??= # ??( [ ??< {
??/ \ ??) ] ??> }
??’ ˆ ??! | ??- ~
However the symbol you showed ??* is not a trigraph symbol. So it is difficult to say what it means.
It seems I have understood what it means. They are wild characters ? and * Simply inside a string literal symbol ? was doubled.:)
