How to implement a callback function

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

Code:

---

#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

---

This is a very simple example of using a callback function

Code:

---

#include <string>
#include <iostream>
using namespace std;

void fcb1()
{
        cout << "In call 1" << endl;
}

void fcb2()
{
        cout << "In call 2" << endl;
}

class cbck
{
        typedef void(*fc)();
        string s1;
        fc fcb;

public:
        cbck(fc fb = fcb1) : fcb(fb) {}

        string getstr() const
        {
                return s1;
        }

        void setstr(const string& s) {
                s1 = s;
                fcb();
        }

        void setcall(fc fb)
        {
                fcb = fb;
        }
};

int main()
{
        cbck c1;

        c1.setstr("s1");
        cout << c1.getstr() << endl;

        c1.setcall(fcb2);
        c1.setstr("s2");

        cout << c1.getstr() << endl;
}

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