[libstdc++] Transforming a string to a primary sort key

[Tim Shen]

Hi there, I'm a libstdc++ developer, contributing C++11 <regex> part.

C++ standard <regex> specifies a function
`regex_traits::transform_primary()` that takes a string, then converts
it to a "primary sort key". However, the standard doesn't specify any
interface to do the actual conversion.

For example, for input "AÀÁÂÃÄÅaàáâãäå" under locale "en_US.UTF-8",
the output could be, but not necessarily, "aaaaaaaaaaaaaa".

Can I get any idea about implementing that function?

Thank you!


-- 
Regards,
Tim Shen