I'm trying to generate a specification for a language using 7bit switch but JFlex won't generate anything. It always says:

Reading "vc.flex"
0 errors, 0 warnings.

Generation aborted.

When I use 8bit or unicode switch, it works fine.

Reading "vc.flex"
Constructing NFA : 276 states in NFA
Converting NFA to DFA :
...............................................................................
.......................................................
138 states before minimization, 121 states in minimized DFA
Writing code to "Scanner.java"
0 errors, 0 warnings.

Generation finished successfully.

I'm using JFlex 1.8.1.