C++ :: Calling Function In DLL

I have this sample code, that calls a function in a DLL. The function Callback is provided to the DLL as an argument, in order for the DLL to notify my program of relevant changes.

sample:

#include <iostream>
#include <conio.h>
#include <windows.h>
#include <winbase.h>
#include "TcAdsDef.h"
#include "TcAdsApi.h"
 using namespace std;
 void _stdcall Callback(AmsAddr*, AdsNotificationHeader*, unsigned long);
 
[Code] ....

I would like to change this code, so that there is a Main class that opens the connection and there are several separate classes (as below) that register themselves for a specific variable and get notifications if that value is changed. The reason for this is that I want to get several notifications for several independent events and I don't want them to mix. I figured this should look something like this:

class.h
#ifndef INACLASS_H
#define INACLASS_H
 #include "Main.h"
 class InAClass {
    public:
        InAClass(Main* mainClass, std::string iolocation);

[Code] ....

Unfortunately this gives me an error:
error: cannot convert 'InAClass::Callback' from type 'void (InAClass::)(AmsAddr*, AdsNotificationHeader*, long unsigned int)' to type 'PAdsNotificationFuncEx {aka void (__attribute__((__stdcall__)) *)(AmsAddr*, AdsNotificationHeader*, long unsigned int)}'

At first I thought this was because I don't have the namespace "using namespace std;" on top, but then I should be able to find something that specifically needs to come from the std namespace and is not marked as such. I don't want to rule the option out, but so far I could not find anything like that.

An alternative explanation might be that the Callback function needs to be global, but if I make it global, how can I distinguish between several Callback functions?