问题
Note that the * in the title is meant to be a placeholder, in my case the culprit was ??[.
I just came over C++ (also "C") escape sequences, formed by double question marks. What was this ever used for and why is it still there?
I have ascii-85 encoded text where double question marks seldom occur and just spent an afternoon ripping the hair from my head while attempting to find a bug in the encoder / decoder, while it was simply the compiler playing tricks on me.
回答1:
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.:)
来源：https://stackoverflow.com/questions/25059452/c-escape-sequence