Callback.cpp

#include <iostream>

class Callback
{
    public:
    virtual void call() = 0;
};

Callback *registered_callback;

void register_callback(Callback *cb)
{
    registered_callback = cb;
}

void call_registered_callbacks()
{
    registered_callback->call();
}

class MyCallback : public Callback 
{
    private:
        int value;
    public:
    MyCallback(int in_value):value(in_value){}

    void call() override
    {
        std::cout << value << std::endl;
    }
};

int main()
{
    auto cb = new MyCallback{10};

    register_callback(cb); 

    std::cout << "lalilala" << std::endl;
    call_registered_callbacks();
}

callback.cpp

#include <iostream>

void *cb_data;
void (*cb_f)(void*);


void register_callback(void (*f)(void*), void *data)
{
    cb_data = data;
    cb_f = f;
}

void call_registered_callbacks()
{
    cb_f(cb_data);
}


void callback(void *data)
{
    int *value;
    value = (int*) data;
    std::cout << *value << std::endl;
}


int main()
{
    int payload = 10;
    register_callback(&callback, &payload); 

    std::cout << "lalilala" << std::endl;
    call_registered_callbacks();
}