#include <iostream>

int main()
{
    std::cout << u8"это строка6" << std::endl;
    return 0;
}

��то строка6

#include <iostream>
#include <windows.h>
#include <fcntl.h>
#include <io.h>
#include <iostream>         // std::wcerr

std::wstring strtows(const std::string &str, UINT codePage)
{
    std::wstring ws;
    int n = MultiByteToWideChar(codePage, 0, str.c_str(), static_cast<int>(str.size()), NULL, 0);
    if (n) {
        ws.resize(n);
        if (MultiByteToWideChar(codePage, 0, str.c_str(), static_cast<int>(str.size()), &ws[0], n) == 0)
            ws.clear();
    }
    return ws;
}

std::string wstostr(const std::wstring &ws, UINT codePage)
{
    // prior to C++11 std::string and std::wstring were not guaranteed to have their memory be contiguous,
    // although all real-world implementations make them contiguous
    std::string str;
    int srcLen = static_cast<int>(ws.size());
    int n = WideCharToMultiByte(codePage, 0, ws.c_str(), srcLen, NULL, 0, 0, NULL);
    if (n) {
        str.resize(n);
        if (WideCharToMultiByte(codePage, 0, ws.c_str(), srcLen, &str[0], n, 0, NULL) == 0)
            str.clear();
    }
    return str;
}

std::string WstringToUtf8(const std::wstring &str)
{
    return wstostr(str, CP_UTF8);
}

std::wstring Utf8ToWstring(const std::string &str)
{

    return strtows(str, CP_UTF8);
}

int main(int argc, char *argv[])
{
    _setmode(_fileno(stdout), _O_U16TEXT);
    std::wcout << Utf8ToWstring(u8"это строка6") << std::endl;
    return 0;
}