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Years ago I wrote a perfectly reasonable comment like /* WTF??!?!!?!???? */ and the old C compiler complained about "invalid trigraph". A syntax error in the middle of a comment!

Took me a while to figure out that "trigraph" was referring to some part of "??!?!!?!????" and not "WTF".

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That's a bug, there is no such thing as an invalid trigraph. ?? followed by any character other than =, /, ', (, ), !, <, >, or - is not a valid trigraph, but that doesn't make it an invalid trigraph, that just makes it not a trigraph, it's perfectly valid to have ??? in a comment, or in a string literal.

Are you telling me that C compilers in the early 90's had bugs and confusing error messages??!!?!??? WTF?!??!?!?

Oh so that's why their called trigraphs, because there's 3 valid states?

Valid Invalid ??? (Exercise for the reader to decide if this is a trigraph or not)

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