This should be replaced with std::aligned_storage to be more portable between compilers and avoid 'clumsy' workaround:
https://github.com/open-source-parsers/jsoncpp/blob/master/src/lib_json/json_value.cpp#L36

In my own JSON implementation I use it like this:
https://github.com/tymonx/OpenRedfish/blob/dev/json/json.cpp#L52