[boost] regexes matching empty strings

From: Michael Goldshteyn (mgoldshteyn_at_[hidden])
Date: 2005-02-18 08:55:08

Why can I not construct a regex of the form: "|abc" (throws exception based 
on REG_EMPTY) for use with regex_match, if I want to match either "abc" or 
the empty string "". I understand thatn in a regex_search the empty string 
would always match (per Perl like semantics), and abc would never be 
considered. But, I want to use this with regex_match, where the empty string 
would have to match the entire string being searched. Work arounds such as 
"(?:)|abc" and "^$|abc" seem to get around this deficiency, but I am 
wondering why it is there in the first place.

Thanks,

Michael Goldshteyn