[Bug other/51711] New: regex.h contains incorrect code

["ryanmolden at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51711

             Bug #: 51711
           Summary: regex.h contains incorrect code
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ryanmolden@gmail.com


The code in regex_replace looks like this

template <typename _Rx_traits, typename _Ch_type>
inline basic_string<_Ch_type>
regex_replace(const basic_string<_Ch_type>& __s,
              const basic_regex<_Ch_type, _Rx_traits>& __e,
              const basic_string<_Ch_type>& __fmt,
              regex_constants::match_flag_type __flags,
              = regex_constants::match_default)
{
    std::string __result;
    regex_replace(std::back_inserter(__result),
                  __s.begin(), __s.end(), __e, __fmt, __flags);
    return __result;
}

However, the std::string is incorrect if you are attempting to use wstring and
wregex here (which should be allowed by all the other code which goes to pains
to use basic_string<_Ch_type>).

This code repros the bug:

#include <regex>
#include <string>

int main(int argc, char **argv)
{
    std::wstring toProcess(L"Bug\r\n");
    std::wstring result = std::regex_replace(toProcess, std::wregex(L"\\r"),
std::wstring(L"\\r"));
    return 0;
}

compiled with:

g++ <filename> -std=c++0x +Wall

In file included from /usr/include/c++/4.6/regex:62:0,
                 from Test.cpp:1:
/usr/include/c++/4.6/bits/regex.h: In function std::basic_string<_Ch_type>
std::regex_replace(const std::basic_string<_Ch_type>&, const
std::basic_regex<_Ch_type, _Rx_traits>&, const std::basic_string<_Ch_type>&,
std::regex_constants::match_flag_type) [with _Rx_traits =
std::regex_traits<wchar_t>, _Ch_type = wchar_t,
std::regex_constants::match_flag_type = std::bitset<11ul>]:
Test.cpp:7:96:   instantiated from here
/usr/include/c++/4.6/bits/regex.h:2225:14: error: could not convert __result
from std::string {aka std::basic_string<char>} to std::basic_string<wchar_t>

on Ubuntu 11.10 Server 64 bit edition with GCC 4.6.1