FSX Proper way to detect variable changes

[JMorrison]

Hey guys, I'm coding a piece of software for my home made cockpit.
What I would like to know is what is the proper or more efficient way to detect when a variable changes its value.
This is an example about how I do it right now:

void processData(Data *pS)
{
        if(pS->myVar) // boolean
        {
                         // do something
        }else{
                         // do something
        }
}

Even when it works, there is a ton of variables I must check on every cycle, I thing there must be a better way to handle this, right?

 

[mgh]

Surely the only way to detect if a variable has changed is to check that the variable itself has changed?

 

[JMorrison]

Surely the only way to detect if a variable has changed is to check that the variable itself has changed?

That's pretty obvious, what I'm asking is if there is a feature in the API that can help optimizing this task.

 

[mgh]

What do you expect such an API to achieve? You could check the SimConnect API in the SDK SimConnect API Reference.

 

[ddawson]

You want something like this:
hr = SimConnect_RequestDataOnSimObject( hSimConnect, A.ID+6000, DATA_DEFINITION_AIRCRAFT_DATA,A.ID, SIMCONNECT_PERIOD_SECOND, SIMCONNECT_DATA_REQUEST_FLAG_CHANGED , NULL, 4, NULL );

 

[JMorrison]

You want something like this:
hr = SimConnect_RequestDataOnSimObject( hSimConnect, A.ID+6000, DATA_DEFINITION_AIRCRAFT_DATA,A.ID, SIMCONNECT_PERIOD_SECOND, SIMCONNECT_DATA_REQUEST_FLAG_CHANGED , NULL, 4, NULL );

Thank you Mr Dawson, I will start reading there.
Your help is always invaluable.

 

[mgh]

If the SIMCONNECT_DATA_REQUEST_FLAG_CHANGED flag is set in SimConnect_RequestDataOnSimObject() then the SDK reads

"Data will only be sent to the client when one or more values have changed. If this is the only flag set, then all the variables in a data definition will be returned if just one of the values changes."

If a variable is a float/double then it could change in the last decimal point without there being a meaningful change.

 

[taguilo]

You could bulid an array with all of the AVars you want to check, then use a loop for testing each one and see which has changed.

Tom

 

[virtuali]

If the SIMCONNECT_DATA_REQUEST_FLAG_CHANGED flag is set in SimConnect_RequestDataOnSimObject() then the SDK reads
If a variable is a float/double then it could change in the last decimal point without there being a meaningful change.

Which is why, the SimConnect_AddToClientDataDefinition, which must be called before requesting any data, has the optional fEpsilon parameter:

fEpsilon
[in, optional] If data is requested only when it changes, a change will only be reported if it is greater than the value of this parameter (not greater than or equal to). The default is zero, so even the tiniest change will initiate the transmission of data. Set this value appropriately so insignificant changes are not transmitted. This can be used with integer data, the floating point fEpsilon value is first truncated to its integer component before the comparison is made (for example, an fEpsilon value of 2.9 truncates to 2, so a data change of 2 will not trigger a transmission, and a change of 3 will do so).

 

[mgh]

Thank you. I missed that!