linuxpimp20

hi i was wondering what you'd catergorize [Rr][Ee][Gg][Ee][Xx] as? It's not really a language or anything right? Also if you use it in code would it slow down your program because the expression(s) need to be evaluated? If so is it really a big performance difference?

DaWei

Regular expression evaluation is a tool. Some languages have such tools built into common libraries, some don't. Regular expression evaluation is a performance hit for simple things that can be done with compare or substring functions, indispensable for complex things. Validating an email address that works for a very large majority is simple, for instance. Validating an email address for 100% compliance with the RFC isn't.

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stevengs

Amen!

(See RFC 822) an example of a valid email address:


:p

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jim mcnamara

regular expressions have a base in math.

The example you posted is more usually called classes, a subset of regular expressions.

DaWei is correct in saying that that RE are builtins and not always there, but that's correct only for older systems.

From XP (.NET) on they are/will be there and any POSIX-compliant unix has to support them. There are even COM objects for VB6 that support them, too.