Advanced MFC Programming

Chapter 16. Context Sensitive Help
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}
}
if(::DdeNameService(m_dwInst, m_hszServiceName, NULL, DNS_REGISTER))
{
szRlt="DDE initialized successfully!";
}
else szRlt="Fail to initialize DDE: Fail to register name service!";
break;
Printf((LPCSTR)szRlt);
Printf("\r\n");
Here CMainFrame::m_dwInst is a DWORD type static variable and CMainFram::DdeCallback(…) is a
static member function. This is because a callback function must be either a global function or a static
member function. Function CMainFrame::Hszize() can be used to obtain a string handle for the name
service and store the handle in static variable CMainFrame::m_hszServiceName. When the application exits,
the name service is unregistered and also, the DDE is uninitialized there. This is implemented in WM_CLOSE
message handler:
void CMainFrame::OnClose()
{
::DdeNameService(m_dwInst, NULL, NULL, DNS_UNREGISTER);
UnHszize();
::DdeUninitialize(m_dwInst);
}
CFrameWnd::OnClose();
Also, the string handle is freed here. In the sample, functions CMainFrame::Hszize() and
CMainFrame:: UnHszize() are implemented for obtaining and freeing string handles respectively:
void CMainFrame::Hszize()
{
m_hszServiceName=::DdeCreateStringHandle(m_dwInst, m_szService, NULL);
Printf("Service name: %s\r\n", m_szService);
}
void CMainFrame::UnHszize()
{
::DdeFreeStringHandle(m_dwInst, m_hszServiceName);
}
Here CMainFrame::m_szService is a static variable.
Monitoring DDE Activities
To monitor the activities of the server, function CMainFrame::Printf(…) is implemented in the
sample. This function imitates the well-known function prinf(…), and outputs a formatted string to the
client window. We can use it exactly the same way as we use function printf(…). Since the view of the
sample is based on class CEditView, it is easy for us to display text in the client window. Since the client
window is solely used for displaying information, we need to set the window’s ES_READONLY style before
the it is created:
BOOL CDDESrvView::PreCreateWindow(CREATESTRUCT& cs)
{
BOOL bPreCreated = CEditView::PreCreateWindow(cs);
cs.style &= ~(ES_AUTOHSCROLL|WS_HSCROLL);
cs.style |= ES_READONLY;
}
return bPreCreated;
Because function CEditCtrl::ReplaceSel(…) is used to output text to the edit view in function
CMainFrame::Printf(…), we further need to prevent the cursor position from being changed by the user
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