I spent more time than I should have yesterday trying to understand
regcomp(), regexec() and regerror() well enough to validate a string
containing an e-mail address string to make sure that: its structure is
correct and neither the username nor the domain contains characters they
shouldn't.

The upshot was that I couldn't do it because I could not write a regex
that would detect spaces in the address because apparently regcomp
doesn't provide any way to anchor a regex to either end of a string, so I
ended up with a negated regex that detects invalid characters in the
string and hasn't a clue whether its syntactically correct:

[^.a-zA-Z0-9@_-]

This does the trick, but no thanks to the man pages regex(3), which
describes the C functions, and regex(7), which describes the regex syntax.
Both are poorly formatted, hard to read, and seem to have omitted useful
information, such as the inability of specifying anchor points in strincs
that DO NOT contain newlines.

So, can any of you do better, i.e. write a regex that CAN validate the
syntax of an e-mail address in terms of its structure and the set of
permitted characters on the username and domain parts (the permitted
character sets are not the same).

Also, if anybody can suggest a better tutorial on using these functions
or suggest another, better, set of C functions for doing the same job,
that would be wonderful.

PS: I did check my old reliable standby text - David Curry's "UNIX
Systems Programming for SVR4", but it wasn't helpful in this case
because, unusually, the set of functions in the C Standard Library have
changed both names and parameters since it was written.


--
Martin    | martin at
Gregorie  | gregorie dot org

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