Convert between C++ WString and String

std::wstring StringToWString(const std::string& str) 
{
    int num = MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, NULL, 0);
    wchar_t *wide = new wchar_t[num];
    MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, wide, num);
    std::wstring w_str(wide);
    delete[] wide;
    return w_str;
}

std::string WStringToString(const std::wstring &wstr)
{
    std::string str;
    int nLen = (int)wstr.length();
    str.resize(nLen, ' ');
    int nResult = WideCharToMultiByte(CP_ACP, 0, (LPCWSTR)wstr.c_str(), nLen, (LPSTR)str.c_str(), nLen, NULL, NULL);
    if (nResult == 0)
    {
        return "";
    }
    return str;
}