write OPC client with LabWindows/CVI

[Marg_SZ]

I'm working on a project that requires communicating with Unidrive through OPC Server. I'm programming with LabWindows/CVI.

I cannot make those function calls work that require SAFEARRAY parameter to be passed in. For example, IOPCGroupAsyncRead( )...

Want to know if anybody has done the same thing successfully. I need your help. Thanks.

[Perry_S]

Hi Marg SZ,

What version of  LabWindows/CVI are you using? Are you seeing any specific errors when trying to use the function calls? 

Perry S.

[Marg_SZ]

Hi Perry,

I'm using LabWindows/CVI 6.0. There is no error messages. I can only read/write item successfully because they do not require SAFEARRAY parameters.

I would appreciate if you can help.

Margaret

[Perry_S]

Hi Margaret,

How are you creating the safe arrays? Is your array 1D or 2D? Are you using the conversion functions in LabWindows/CVI?

Regards,

Perry S.

[Marg_SZ]

My code is as follows. Some of the variables are global. Thanks.

void GroupAsyncRead(void)
{
   OPCAutomationObj_OPCItems ppItems;
   OPCAutomationObj_OPCItem  ppItem;
   long numItems, hvalue, i;
   SAFEARRAY *serverHandles, *errors;  SAFEARRAYBOUND rgsabound[1];

   OPCAutomation_IOPCGroupGetOPCItems(OPCGroupHandle, &Error_Info, &ppItems);  
   OPCAutomation_OPCItemsGetCount(ppItems, &Error_Info, &numItems);
   rgsabound[0].lLbound = 0;
   rgsabound[0].cElements = numItems;

   serverHandles = SafeArrayCreate(VT_I8, 1, rgsabound);
   for(i=0; i < numItems; i++)
   {
      OPCAutomation_OPCItemsItem(ppItems, &Error_Info, CA_VariantInt(i+1), &ppItem);
      OPCAutomation_OPCItemGetServerHandle(ppItem, &Error_Info, &hvalue);
      SafeArrayPutElement(serverHandles, &i, &hvalue);
   }
   OPCAutomation_IOPCGroupAsyncRead(OPCGroupHandle, &Error_Info, numItems, &serverHandles,
                                                  errors, GetTransactionID(), &cancelID);
   asyncReadInProgress = 1;
   OPCAutomation_DIOPCGroupEventRegOnAsyncReadComplete(OPCServerHandle, ProcessGroupAsyncReadComplete, NULL, 1, NULL);
   SafeArrayDestroy(serverHandles);
   SafeArrayDestroy(errors);
}

[Marg_SZ]

Sorry, I pasted it wrongly in the previous post. "errors" is passed by reference as follows.

   OPCAutomation_IOPCGroupAsyncRead(OPCGroupHandle, &Error_Info, numItems, &serverHandles,
                                                  &errors, GetTransactionID(), &cancelID);

[Perry_S]

Hi Margaret,

I think that you are using the wrong functions to create your safe arrays. Please use the functions that are located in the ActiveX Library, Array section. 

Perry S.

[Perry_S]

Hi Margaret,

Where did you get the functions that you are using to create the safearrays? Which CVI library?

Perry S.

[Marg_SZ]

Perry,

Those are functions of Windows SDK. I haven't tried your suggestion on using ActiveX Array functions.

Thank you for following on this.

Margaret

[Perry_S]

Hi Margaret,

Let me know how it works when you try it.

Perry S.