How to get string with pattern from std::regex in VC++ 2010

Question

Can I get the string with regular expression from std::regex? Or should I save it somewhere else if I want to use it later?

In boost you can do this:

boost::regex reg("pattern");
string p = reg.str();

or use << operator

cout << reg; will print pattern.

but in std::regex there is no str() or operator<<. Should I save my string somewhere else or I just can't find it?

In debugger I can see what's in std::regex.

Answer 1

I just looked in N3225, section 28.4 (header <regex> synopsis) and indeed, the basic_regex template has no member function str, and there are no operator<< provided.

The paragraph 28.8/2 provides a little insight on this :

Objects of type specialization of basic_regex are responsible for converting the sequence of charT objects to an internal representation. It is not specified what form this representation takes, nor how it is accessed by algorithms that operate on regular expressions.

What I understand is that the standard mandates that basic_regex can be constructed from const charT * but does not require the implementation to keep this string.

Answer 2

The MSDN docs seem to show that there's no publicly accessible way to retrieve the regex pattern from a constructed object, so I would say that you need to save the string yourself.