Is there another way to get a COleDateTime object from another dialog using SendMessage?

Question

I have a registered user message. This is the handler:

afx_msg LRESULT CChristianLifeMinistryEditorDlg::OnGetDate(WPARAM wParam, LPARAM lParam)
{
    const auto eDateType = gsl::narrow<CInsertDateDlg::EnumDateType>(wParam);

    if (eDateType == CInsertDateDlg::EnumDateType::Start)
    {
        return CInPlaceDT::GetLongDate(m_datStartDate);
    }

    if (eDateType == CInsertDateDlg::EnumDateType::End)
    {
        return CInPlaceDT::GetLongDate(m_datEndDate);
    }

    if (eDateType == CInsertDateDlg::EnumDateType::Meeting)
    {
        return CInPlaceDT::GetLongDate(m_pEntry->GetMeetingDate());
    }

    return CInPlaceDT::GetLongDate(COleDateTime::GetCurrentTime());
}

The referenced function is:

long CInPlaceDT::GetLongDate(COleDateTime timDate) noexcept
{
    const long lDate = (timDate.GetYear() * 10000) +
                    (timDate.GetMonth() * 100 ) +
                     timDate.GetDay();

    return lDate;
}

I use the code like this (some lines stripped out for simplicity):

// 1. CEditTextDlg
// 2. CSMCustomizeDlg
// 3. CChristianLifeMinistryEditor
const CWnd* pParent = GetParent()->GetParent()->GetParent();
if (pParent != nullptr)
{
    COleDateTime datToUse;
    long lDate{};

    lDate = gsl::narrow<long>(pParent->SendMessage(theApp.UWM_GET_DATE_MSG,
        gsl::narrow<WPARAM>(CInsertDateDlg::EnumDateType::Start)));
    CInPlaceDT::GetOleDateTime(lDate, datToUse);

    lDate = gsl::narrow<long>(pParent->SendMessage(theApp.UWM_GET_DATE_MSG,
        gsl::narrow<WPARAM>(CInsertDateDlg::EnumDateType::End)));
    CInPlaceDT::GetOleDateTime(lDate, datToUse);

    lDate = gsl::narrow<long>(pParent->SendMessage(theApp.UWM_GET_DATE_MSG,
        gsl::narrow<WPARAM>(CInsertDateDlg::EnumDateType::Meeting)));
    CInPlaceDT::GetOleDateTime(lDate, datToUse);
}

The second referenced function is:

void CInPlaceDT::GetOleDateTime(long lDate, COleDateTime &timDate) noexcept
{
    const auto nYear = lDate / 10000;
    const auto nMonth = (lDate / 100) % 100;
    const auto nDay = lDate % 100;

    timDate.SetDateTime(nYear, nMonth, nDay, 0, 0, 0);
}

This concept works. It converts the date to a long, returns it via the message and is converted back to a date object.

I just wondered if I could pass the object as a date variable? This is all within the same process. A grandchild dialog is getting a date from the grandparent dialog.

---

Update

I tried to follow the suggestion in the comments:

afx_msg LRESULT CChristianLifeMinistryEditorDlg::OnGetDate(WPARAM wParam, LPARAM lParam)
{
    const auto eDateType = gsl::narrow<CInsertDateDlg::EnumDateType>(wParam);

    if (eDateType == CInsertDateDlg::EnumDateType::Start)
    {
        return gsl::narrow<LRESULT>(&m_datStartDate); // CInPlaceDT::GetLongDate(m_datStartDate);
    }

    if (eDateType == CInsertDateDlg::EnumDateType::End)
    {
        return gsl::narrow<LRESULT>(&m_datEndDate); // CInPlaceDT::GetLongDate(m_datEndDate);
    }

    if (eDateType == CInsertDateDlg::EnumDateType::Meeting)
    {
        return gsl::narrow<LRESULT>(&(m_pEntry->GetMeetingDate())); // CInPlaceDT::GetLongDate(m_pEntry->GetMeetingDate());
    }

    return 0;
    // return CInPlaceDT::GetLongDate(COleDateTime::GetCurrentTime());
}

But it does not like:

return gsl::narrow<LRESULT>(&(m_pEntry->GetMeetingDate())); 

It says:

error C2102: '&' requires l-value

Answer 1

As other window function do it too. Pass a pointer in LPARAM. Save the value in that pointer

afx_msg LRESULT CChristianLifeMinistryEditorDlg::OnGetDate(WPARAM , LPARAM lParam)
{
   *reinterpret_cast<COleDateTime*>(lParam) = myValue;

Remember that a COleDateTime is just a DATE (is a double). You may use a VARIANT* to that may handle all types of data (even an empty/null COleDateTime)

In detail: Use VT_NULL or VT_EMPTY for COleDateTime::null. For COleDateTime::error/invalid you can use VT_ERROR with the value E_INVALIDARG or any suitable.

For a COleDateTime::valid just store the m_dt member in the VARIANT with VT_DATE.