QUESTION - How to add args to callback function

[EusebioAlsoliman]

I'm trying to use a callback similar to the one in https://www.open62541.org/doc/v1.4.0/tutorial_server_datasource.html#variable-value-callback

In the example, the function afterWriteTime() is static and also doesn't need additional arguments or data. However, in my case, I need to pass extra arguments and make calls to functions. How can I do that?

Thanks in advance.

[ccvca]

You may either use the nodeContext or the sessionContext for this. Own arguments are not possible in C.

[EusebioAlsoliman]

You may either use the nodeContext or the sessionContext for this. Own arguments are not possible in C.

From the example I have seen that the callback functions should have this structure:

afterWriteTime(UA_Server *server,
               const UA_NodeId *sessionId, void *sessionContext,
               const UA_NodeId *nodeId, void *nodeContext,
               const UA_NumericRange *range, const UA_DataValue *data){
               // Code to be executed
}

But I don't know exactly how I can get the data from that nodeContext pointer. Also, how UA_Server_setNodeContext() really works?

Thanks in advance.

[ccvca]

Use UA_Server_setNodeContext to set a pointer, which then can be used in the callback again:

// your Initialization

pMyVariable = (mytype*) malloc(sizeof(mytype));
UA_Server_setNodeContext(pServer, nodeId, pMyVariable);


afterWriteTime(UA_Server *server,
               const UA_NodeId *sessionId, void *sessionContext,
               const UA_NodeId *nodeId, void *nodeContext,
               const UA_NumericRange *range, const UA_DataValue *data){
               /// Get your variable again
               pVariableFromContext = (mytype*) nodeContext;

               // Code to be executed
}

PS: All NULL-Checks are missing!

[EusebioAlsoliman]

Use UA_Server_setNodeContext to set a pointer, which then can be used in the callback again:

// your Initialization

pMyVariable = (mytype*) malloc(sizeof(mytype));
UA_Server_setNodeContext(pServer, nodeId, pMyVariable);


afterWriteTime(UA_Server *server,
               const UA_NodeId *sessionId, void *sessionContext,
               const UA_NodeId *nodeId, void *nodeContext,
               const UA_NumericRange *range, const UA_DataValue *data){
               /// Get your variable again
               pVariableFromContext = (mytype*) nodeContext;

               // Code to be executed
}

PS: All NULL-Checks are missing!

Ok, now I've understood how it works, thanks.