warning C4244 : VS 2019

Question

While building a VC++ solution in VS 2019 I am getting the below error. I did some googling and couldn't find a solution.

" warning C4244: 'argument': conversion from 'wchar_t' to 'const _Elem', possible loss of data"

It arises from a file called xtring:

C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.27.29110\include\xstring(2390,23):

What could be the reason. Could someone please help?

Answer 1

Just write any code, that includes <xstring>. Warning is here:

template <class _Iter>
    void _Construct(_Iter _First, const _Iter _Last, input_iterator_tag) {
        // initialize from [_First, _Last), input iterators
        _Tidy_deallocate_guard<basic_string> _Guard{this};
        for (; _First != _Last; ++_First) {
            push_back(*_First); // <==== Here we have this warning
        }

        _Guard._Target = nullptr;
    }

C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.27.29110\include\xstring(2390,23): warning C4244: 'argument': conversion from 'wchar_t' to 'const _Elem', possible loss of data
with
[
_Elem=char
]

Answer 2

More details: it happens in code like this:

std::string foo("123");
std::wstring bar(foo.begin(), foo.end());