You can use the SWbemDateTime object as explained here: https://devblogs.microsoft.com/oldnewthing/20121102-00/?p=6183

Here is the relevant piece of code:

BOOL FileTimeFromCIMDateTime(__in LPCWSTR psz, __out LPFILETIME pft)
{
 BOOL fSuccess = FALSE;
 ISWbemDateTime *pDateTime;
 HRESULT hr = CoCreateInstance(__uuidof(SWbemDateTime), 0,
                 CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDateTime));
 if (SUCCEEDED(hr)) {
  BSTR bstr = SysAllocString(psz);
  if (bstr) {
   hr = pDateTime->put_Value(bstr);
   if (SUCCEEDED(hr)) {
    BSTR bstrFT;
    hr = pDateTime->GetFileTime(VARIANT_FALSE, &bstrFT);
    if (SUCCEEDED(hr)) {
     __int64 i64FT = _wtoi64(bstrFT);
     pft->dwLowDateTime = LODWORD(i64FT);
     pft->dwHighDateTime = HIDWORD(i64FT);
     fSuccess = TRUE;
     SysFreeString(bstrFT);
    }
   }
   SysFreeString(bstr);
  }
  pDateTime->Release();
 }
 return fSuccess;
}

Another solution is to port the .NET source to C++, since .NET is open source https://referencesource.microsoft.com/#System.Management/ManagementDatetime.cs,45057a40319a1c83