How to implement a callback function

[Nico1980]

Hello,

I would like to properly implement a callback function, but I have no idea how. I am trying to make a DLL, for now this DLL should have a number of variables that are stored in a 2D array. Using the set function in the interface I can select a variable in this 2D array (row and column index) and change its value.

Using the get function I can verify that the change was successful, but I would like to be notified about this change automatically. I have been told this could be done using a callback function, but I have no idea how to implement that.

Could somebody please provide me with an example and/or explanation for a proper implementation to trigger the callback function if one of the values in the 2D array changes and how to catch the resulting event?

Many thanks in advance, Nico

#pragma once

#if !defined(DLL)
#define DLL __declspec(dllimport)
#endif

#if !defined(IDLL)
#define IDLL DLL
#endif

#if defined(__cplusplus)
extern "C" {
#endif

	// callback function
	// long EventType: Not sure what kind of event types are available
	// long Column: The column.
	// long Row: The row.
	// long EventCode: e.g. 0 = decreased, 1 = increased
	// long EventDataLong: Not sure, but I was told we would need a parameter.
	// double EventDataDouble : The current value of the variable
	typedef void (__stdcall *OnExampleParameterChangedEvent)(long EventType,
		long Column,
		long Row,
		long EventCode,
		long EventDataLong,
		double EventDataDouble);

	// Attach callback function handler
	IDLL long __stdcall ExampleAttachParameterChangedEvent(OnExampleParameterChangedEvent ParameterChanged);


	// Read the state of a Value.
	// long Column: The column.
	// long Row: The row.
	// long* State: The state of the parameter
	IDLL long __stdcall ExampleGetValue(long Column, long Row, long* State);

	// Sets the state of a Value.
	// long Column: The column.
	// long Row: The row.
	// long State: The state of the parameter
	IDLL long __stdcall ExampleSetValue(long Column, long Row, long State);


#if defined(__cplusplus)
}
#endif