Re: [Boost-users] Boost.Regex vs. Boost.Spirit

From: John Maddock (john_at_[hidden])
Date: 2008-04-02 11:32:56

Boris wrote:
> Can anyone tell me why Boost.Spirit (which reuses Boost.Regex for
> regular expressions) works while the code below where Boost.Regex is
> used directly can not be compiled?
>
> std::string in = "test";
>
> boost::wregex expr(L"test");
> boost::match_results<std::string::const_iterator> what;
> boost::regex_search(in, what, expr); // COMPILER ERROR
>
> std::string out;
> boost::spirit::rxstrlit<wchar_t> expr2(L"test");
> boost::spirit::parse(in.c_str(), expr2[boost::spirit::assign_a(out)]);
>
> The basic problem is of course that the regular expressions are based
> on wchar_t while the input string is based on char. Thus I'm not so
> much surprised why Boost.Regex does not work.

Right, by design that doesn't compile.

> I'm much more surprised
> though that my compiler (VC++ 2008) doesn't report an error with the
> code above which uses Boost.Spirit.
>
> I don't know why the code using Boost.Spirit compiles (is this
> implementation-dependent or guaranteed behavior)? It would make using
> regular expressions in templates much easier though as regular
> expressions don't seem to depend on the Char type of strings
> (assuming this is a feature I can rely on)?

Well that depends on the regular expression, something like 
"[\x{0370}-\x{03ff}]+" most certainly does depend upon the character type! 
;-)

John.