narrow-conversion uses insufficient input char type

[dani@…]

Test runs exhibit this problem:

compile-c-c++ ..\..\..\bin.v2\libs\date_time\test\teststreams.test\msvc-12.0\debug\address-model-64\posix_time\teststreams.obj
teststreams.cpp
boost/date_time/posix_time/posix_time_legacy_io.hpp(83) : warning C4244: 'argument' : conversion from 'wchar_t' to 'char', possible loss of data
        posix_time\teststreams.cpp(144) : see reference to function template instantiation 'std::basic_istream<wchar_t,std::char_traits<wchar_t>> &boost::posix_time::operator >><wchar_t>(std::basic_istream<wchar_t,std::char_traits<wchar_t>> &,boost::posix_time::time_duration &)' being compiled

The current implementation uses std::stringstream::narrow(char) with its 'char' input parameter type to transform 'charT' chars taken from a std::basic_istream<charT> into 'char' chars. This is most likely not what is intended if 'charT' is wider than 'char'.

Tests were run against Boost version 1.55.0 and latest 'development' branch using vc10, vc11, and vc12. Test logs are attached.

[dani@…]

Pull request ​https://github.com/boostorg/date_time/pull/1 fixes this problem. The attached test logs show the warning is gone now.