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  5. QuickOPC-Classic in COM
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  9. Can Develop OPC XML DA C++ client in Visual Studio 2015?

Can Develop OPC XML DA C++ client in Visual Studio 2015?

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26 Sep 2016 09:53 #4381 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hi,

Yes its clear now for me, when comes to COM connection(QuickOPC Component).
I debugged C# apps to know how the connection is happening to XML Server. Now, I don't want to bother much about connection as QuickOPC is taking care of that.

And I still stuck in the same issue as DAVtqPtr is converted in to string (DAVtqPtr->ToString).
DAVtqPtr is having DAVtqResultPtr->Vtq value which null always and am not able to see quality parameter in
ResultArray. Plese help me out.

Please bare with me as i am new to this area and correct me if am wrong.

Thanks.

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26 Sep 2016 09:38 #4380 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hi, Can i get any help on this exception please.

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26 Sep 2016 08:55 #4379 by support
Replied by support on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
I what you are trying to do, the COM component is our QuickOPC product. COM is just used between your code, and QuickOPC. QuickOPC then connect to a Web service, that is an OPC XML-DA server.

I do not understand what are you trying to do with remote debugging. You should simply debug locally. And, we are not that much interested in what happens *inside* the ReadItem method itself - we just need to know the details of the exception it throws.

And, I do not understand why - at least according to the picture - you have now switched to debugging the C# demo - you have said that (as opposed to your app) it works well, so why debug it?

Thank you
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26 Sep 2016 07:46 #4378 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hi Team,

When I am trying to debug OPC XML DA Csharp application I am getting a remote debugging error, Am I able to enter into easyDAClient1.ReadItem(serverUrlTextBox.Text,new DAItemDescriptor(itemIdTextBox.Text{ NodePath = nodePathTextBox.Text })) this function via remote debugging? Please refer attached image.

As I understand, XML DA client should connect to Webservice to get the data. In our sample code we still use COM components to connect to XML server(reusing OPC DA connection)? How this connection is happening to XML server? COM should not come into the picture right? or this COM component used only to connect XML server?

Please correct my understanding if I am wrong.

Thanks.
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23 Sep 2016 10:17 #4375 by support
Replied by support on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Thank you. It is weird - the code accesses the same server, and even the first item is the same as in the demo app, therefore it should work.

The only thing that can bring us closer is examining the exception details (Message, possibly InnerException, etc.). Can you change the code for that, or do you need help with it?

Regards
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23 Sep 2016 10:08 #4374 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hi,

The OPC XML-DA enabled demo application can read data from XML server, I guess there is no issue with firewall settings. Refer attached image.

As of now I am trying with demo server which OPClabs providing, I can handle exception when I write production code. But, My doubt is that, this code could not fetch the values from demo server, as demo application can fetch. Is it kind of any logical issue or syntax based.

Please help.
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23 Sep 2016 09:49 #4372 by support
Replied by support on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
This example does not have the error handling that the production code should.
It is likely that there was some error during reading. Then, the Vtq in the result object is null, and instead, the Exception property contains the information about the problem.

Do you have firewall open, in order to access our demo server?

To test that, simply run the OPC XML-DA enabled, prebuild demo application that comes with the product. That one DOES have error handling in it, and shows the error properly.

Or, are you already trying to connect to your own server?

The production-ready code should test the Exception property of the result first, and if it is not null, handle it accordingly (you can, for example, print out the Message property of the Exception). Only if the Exception is null, the Vtq is non-null.
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23 Sep 2016 09:40 #4371 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hi,

I am getting unhandled exception(Unhandled exception at 0x74D0DB18 )on below line,

_variant_t vtqAsString(DAVtqPtr->ToString);

DAVtqPtr pointer is going null while reading DAVtqResultPtr->Vtq.

Any help please.

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23 Sep 2016 09:07 #4367 by Vasanth
Replied by Vasanth on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Thanks a lot, let me try n get back to you if any help required.

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23 Sep 2016 08:38 #4366 by support
Replied by support on topic Can Develop OPC XML DA C++ client in Visual Studio 2015?
Hello.

For start, take the existing ReadMultipleItems example, and replace the main function with the following one:
int _tmain(int argc, _TCHAR* argv[])
{
    // Initialize the COM library
    CoInitialize(NULL);
 
    // Instatiate the EasyOPC-DA client object
    _EasyDAClientPtr ClientPtr(__uuidof(EasyDAClient));
 
    _DAReadItemArgumentsPtr ReadItemArguments1Ptr(_uuidof(DAReadItemArguments));
    ReadItemArguments1Ptr->ServerDescriptor->UrlString = L"http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx";
    ReadItemArguments1Ptr->ItemDescriptor->ItemId = L"Dynamic/Analog Types/Double";
 
    _DAReadItemArgumentsPtr ReadItemArguments2Ptr(_uuidof(DAReadItemArguments));
    ReadItemArguments2Ptr->ServerDescriptor->UrlString = L"http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx";
    ReadItemArguments2Ptr->ItemDescriptor->ItemId = L"Dynamic/Analog Types/Double[]";
 
    _DAReadItemArgumentsPtr ReadItemArguments3Ptr(_uuidof(DAReadItemArguments));
    ReadItemArguments3Ptr->ServerDescriptor->UrlString = L"http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx";
    ReadItemArguments3Ptr->ItemDescriptor->ItemId = L"Dynamic/Analog Types/Int";
 
    _DAReadItemArgumentsPtr ReadItemArguments4Ptr(_uuidof(DAReadItemArguments));
    ReadItemArguments4Ptr->ServerDescriptor->UrlString = L"http://opcxml.demo-this.com/XmlDaSampleServer/Service.asmx";
    ReadItemArguments4Ptr->ItemDescriptor->ItemId = L"Dynamic/Analog Types/Int[]";
 
    CComSafeArray<VARIANT> ArgumentsArray(4);
    ArgumentsArray.SetAt(0, _variant_t((IDispatch*)ReadItemArguments1Ptr));
    ArgumentsArray.SetAt(1, _variant_t((IDispatch*)ReadItemArguments2Ptr));
    ArgumentsArray.SetAt(2, _variant_t((IDispatch*)ReadItemArguments3Ptr));
    ArgumentsArray.SetAt(3, _variant_t((IDispatch*)ReadItemArguments4Ptr));
 
    LPSAFEARRAY pArgumentsArray = ArgumentsArray.Detach();
    CComSafeArray<VARIANT> ResultArray(ClientPtr->ReadMultipleItems(&pArgumentsArray));
    ArgumentsArray.Attach(pArgumentsArray);
 
    for (int i = ResultArray.GetLowerBound(0); i <= ResultArray.GetUpperBound(0); i++)
    {
        _DAVtqResultPtr DAVtqResultPtr(ResultArray[i]);
        _DAVtqPtr DAVtqPtr(DAVtqResultPtr->Vtq);
        _variant_t vtqAsString(DAVtqPtr->ToString);
        _tprintf(_T("results(%d).Vtq.ToString(): %s\n"), i, vtqAsString.bstrVal);
    }
 
    // Release all interface pointers BEFORE calling CoUninitialize()
    ResultArray.Destroy();
    ClientPtr = NULL;
 
    CoUninitialize();
 
    TCHAR line[80];
    _putts(_T("Press Enter to continue..."));
    _fgetts(line, sizeof(line), stdin);
    return 0;
}

I hope this helps. Le me know when/if you need more.
Best regards

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  1. Forum
  3. Discussions
  5. QuickOPC-Classic in COM
  7. Reading, Writing, Subscriptions, Property Access
  9. Can Develop OPC XML DA C++ client in Visual Studio 2015?
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