I didn't see this in the reported bugs so I'm not sure whether its a known problem or not.

C:\boost\>timer Enter expression (or "quit" to exit): ([[:digit:]]{1,}|[[:space:]]{1,}){1,}[[:alpha:]]{1,} Enter string to search (or "quit" to exit): 22222222222222222222

abnormal program termination

Um yes, the program should catch the exception and report the cause: the regex matching functions can throw if the expression starts consuming too many cycles, in this case you've got the classic: ((something that matches)+)+(something that doesn't match) expression, that will cause any Perl style regex-engine to fall over. Boost.Regex does so by throwing an exception, most others just go on thrashing away indefinitely. Decide for yourself which is better! John.