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Passing arrays and/or structs

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19 Mar 2018 18:53 #6165 by support

Replied by support on topic Passing arrays and/or structs

Subscribing to arrays is no different from subscribing to scalar items. You specify parameters as usual, including the ItemID of the array item, and call the subscribe method. In the event notification, the value that you will receive will be an array.

Example (some subscribed items are scalars and some are arrays): opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...%20various%20data%20types.html

Similarly, writing to array items is the same as writing scalars. Just pass in an array as a value to the Write call.

Example: opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...rite%20an%20array%20value.html

OPC "Classic" (which is what EasyDAClient is for) has no notion of "structures", therefore it cannot be directly done - no matter which server or client you use. There are workarounds, such as that the structure may be represented as multiple items in a branch - but then you lose on atomicity of operations. Anyway, it's the server who dictates how this is done - not us, on the client side.

The newer OPC Unified Architecture can work with "structures" (custom data types), and our EasyUAClient does have a support for it.

Best regards

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