very basic regex scenario works different than my expectation on libstdc++-v3

Question

I\'m getting a different behavior than my expectation (and also different than Microsoft C++).

Consider the following test.cpp file:

#include 

        

Answer 1

is still largely unimplemented in libstdc++: http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2011