How to know if a particular CWPlot already exists in a CWGraph (VC++)?

Question

I would like to add a CWPlot to a CWGraph only if this plot doesn't already
exist within the CWPlots collection.
The problem is that when I call "myGraph.GetPlots().item((COleVariant)
"PlotN")", an exception is throwned if the CWPlot named "PlotN" doesn't
exist.
I do have a workaround : testing all the names of CWPlots collection untill
I find (or not) the right name, but as I have a lot of plots in my graph, it
is very time expensive.
Is there a more elegant way of knowing a plot presence in a graph ?

Answer 1

Georges:
Exceptions are the way that C++ handles all errors, and it's okay to catch exceptions yourself and process them however you like. In this case, for example, I would recommend trying the Item() call and catching the resulting exception. Examine the exception, and if it is one complaining about an "Invalid Index", then you can add the plot and suppress the exception from propagating up the call stack. Here's an example of what I mean:
//================================================​==============================
// Return the requested plot. If it's not there, then add it and return it.
//================================================​==============================
CCWPlot CGeorgesDlg:martGetPlot(CCWGraph &graph, LPCTSTR name)
CCWPlot plot;
try {
plot = graph.GetPlots().Item(COleVariant(name));
catch(COleDispatchException *e) {
// If it's not the exception we're looking for, let it go up the call
// stack, otherwise ignore it.
if(e->m_scError != 0x800A0005) /* invalid index */
throw e;
e->Delete();
// If an exception occured, then add the plot.
if(plot.m_lpDispatch == NULL)
plot = graph.GetPlots().Add();
plot.SetName(name);
return plot;
You could use this helper method to access plots. For example:
void CGeorgeDlg:nModifyPlot()
SmartGetPlot(m_graph,"Plot X").SetEnabled
(TRUE);
// or
CCWPlot MyPlot = SmartGetPlot(m_graph,"Plot Y");
// work with MyPlot variable....
I hope this helps,
Chris W.
National Instruments