regular expressions using flex: max and min length

neioo · 07-30-2009, 08:59 AM

Hello,

I'm using flex and bison to check the correctness of a username, so I have this regexp:

Code:

[A-za-z0-9]+([\.\-]?[A-Za-z0-9]+)*

This works ok for me: usernames start with a letter or number and can have '.' and '-' surrounded by at least one letter or number.

But now, I want to set a minimum and a maximum length of the username, I tried:

Code:

([A-za-z0-9]+([\.\-][A-Za-z0-9]+)*){3,22}

But this doesn't work, because it counts the number of times that the regexp is applied and not count the number of characters of the array.

Is there a way to apply two regexp at same time? like an "and" operator, if so, I could use something like:

Code:

[A-za-z0-9]+([\.\-]?[A-Za-z0-9]+)* AND .{3,22}

Or is there a way to count total characters of an input and apply a regexp at same time?

I think it must be easy to do, but by now my solution is to first check length with strlen and then check correctness using flex.

One link to a webpage lighting the solution will be ok, you don't need to give me the correct regexp.

Thanks in advance.

ntubski · 07-30-2009, 08:51 PM

Maybe you can use yylen (see User Values). I don't think there is any simple way of AND'ing two regexps together, even though regular languages are closed under intersection.