How can I match C-style comments?

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You might be tempted to try something like this:

     "/*".*"*/"       // WRONG!

or, worse, this:

     "/*"(.|\n)"*/"   // WRONG!

The above rules will eat too much input, and blow up on things like:

     /* a comment */ do_my_thing( "oops */" );

Here is one way which allows you to track line information:

     <INITIAL>{
     "/*"              BEGIN(IN_COMMENT);
     }
     <IN_COMMENT>{
     "*/"      BEGIN(INITIAL);
     [^*\n]+   // eat comment in chunks
     "*"       // eat the lone star
     \n        yylineno++;
     }