Error(s):

source_file.cpp:8:10: warning: unused variable 'var' [-Wunused-variable]
    bool var = std::isspace(ustr[0],std::locale());
         ^
In file included from source_file.cpp:2:
In file included from /usr/include/c++/v1/locale:182:
/usr/include/c++/v1/__locale:705:44: error: implicit instantiation of undefined template 'std::__1::ctype<char16_t>'
    return use_facet<ctype<_CharT> >(__loc).is(ctype_base::space, __c);
                                           ^
source_file.cpp:8:21: note: in instantiation of function template specialization 'std::__1::isspace<char16_t>' requested here
    bool var = std::isspace(ustr[0],std::locale());
                    ^
/usr/include/c++/v1/__locale:427:53: note: template is declared here
template <class _CharT> class _LIBCPP_TYPE_VIS_ONLY ctype;
                                                    ^
/usr/include/c++/v1/__locale:186:54: error: implicit instantiation of undefined template 'std::__1::ctype<char16_t>'
    return static_cast<const _Facet&>(*__l.use_facet(_Facet::id));
                                                     ^
/usr/include/c++/v1/__locale:705:12: note: in instantiation of function template specialization 'std::__1::use_facet<std::__1::ctype<char16_t> >' requested here
    return use_facet<ctype<_CharT> >(__loc).is(ctype_base::space, __c);
           ^
source_file.cpp:8:21: note: in instantiation of function template specialization 'std::__1::isspace<char16_t>' requested here
    bool var = std::isspace(ustr[0],std::locale());
                    ^
/usr/include/c++/v1/__locale:427:53: note: template is declared here
template <class _CharT> class _LIBCPP_TYPE_VIS_ONLY ctype;
                                                    ^
1 warning and 2 errors generated.