lex: default rule for unrecognized strings

Question

In ocamllex, I can use _ as a lexer rule to match any string that does not match previously defined rules, and raise errors. How can achieve this in lex/flex?

Answer 1

Typically, you would define a rule like this, which would go at the very end:

.|\n         { /* process default here */ }

This rule will match any character that wasn't matched by any other rule.

Hope this helps!