In the MFC multi-document program, closing a document from the menu has different effects than directly clicking the x in the upper right corner.

In the MFC multi-document program, closing a document from the menu has different effects than directly clicking the x in the upper right corner.

If the document content is modified, the former will ask the user whether to save the modifications; the latter will close directly without saving the modifications.
The reason is that when closing from the menu, calling OnClose will definitely call SaveModified(), the source code is as follows

/
// Standard file menu commands

void CDocument::OnFileClose()
{
    
    
	if (!SaveModified())
		return;

	// shut it down
	OnCloseDocument();
		// this should destroy the document
}

When clicking x to close, the CanCloseFrame() function will determine whether to save the document. The source code is as follows:

BOOL CDocument::CanCloseFrame(CFrameWnd* pFrameArg)
	// permission to close all views using this frame
	//  (at least one of our views must be in this frame)
{
    
    
	ASSERT_VALID(pFrameArg);
	UNUSED(pFrameArg);   // unused in release builds

	POSITION pos = GetFirstViewPosition();
	while (pos != NULL)
	{
    
    
		CView* pView = GetNextView(pos);
		ASSERT_VALID(pView);
		CFrameWnd* pFrame = pView->GetParentFrame();
		// assume frameless views are ok to close
		if (pFrame != NULL)
		{
    
    
			// assumes 1 document per frame
			ASSERT_VALID(pFrame);
			if (pFrame->m_nWindow > 0)
				return TRUE;        // more than one frame refering to us
		}
	}

	// otherwise only one frame that we know about
	return SaveModified();
}

SaveModified()It can be seen that the statement will only be executed when the window of the parent frame is 0 , and TRUE will only be returned in other cases. When using multi-document programming, be careful to add SaveModified()statements to your own overloaded CanCloseFrame() for the sake of document security.

How to save silently without asking the user?

CDocument::SaveModified()The implementation is as follows:

BOOL CDocument::SaveModified()
{
    
    
	if (!IsModified())
		return TRUE;        // ok to continue

	// get name/title of document
	CString name;
	if (m_strPathName.IsEmpty())
	{
    
    
		// get name based on caption
		name = m_strTitle;
		if (name.IsEmpty())
			VERIFY(name.LoadString(AFX_IDS_UNTITLED));
	}
	else
	{
    
    
		// get name based on file title of path name
		name = m_strPathName;
		if (afxData.bMarked4)
		{
    
    
			AfxGetFileTitle(m_strPathName, name.GetBuffer(_MAX_PATH), _MAX_PATH);
			name.ReleaseBuffer();
		}
	}

	CString prompt;
	AfxFormatString1(prompt, AFX_IDP_ASK_TO_SAVE, name);
	switch (AfxMessageBox(prompt, MB_YESNOCANCEL, AFX_IDP_ASK_TO_SAVE))
	{
    
    
	case IDCANCEL:
		return FALSE;       // don't continue

	case IDYES:
		// If so, either Save or Update, as appropriate
		if (!DoFileSave())
			return FALSE;       // don't continue
		break;

	case IDNO:
		// If not saving changes, revert the document
		break;

	default:
		ASSERT(FALSE);
		break;
	}
	return TRUE;    // keep going
}

It can be seen that the "save" action is actually performed DoFileSave(), so developers can consider executing this function when the user performs certain actions and silently save the current editing results without popping up a dialog box for user confirmation.