C++ Converting to a wstring

So I came across this code sample which works well for me. I have pasted it here for convenience

std::wstring convert(const std::string& input)
{
    try
    {
        std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
        return converter.from_bytes(input);
    }
    catch(std::range_error& e)
    {
        size_t length = input.length();
        std::wstring result;
        result.reserve(length);
        for(size_t i = 0; i < length; i++)
        {
            result.push_back(input[i] & 0xFF);
        }
        return result;
    }
}

I am having difficulty understanding this statement

result.push_back(input[i] & 0xFF);

can anyone please explain why each character in the string is being ANDed with 0xFF(11111111) ?