using a callback function from a 3rd party api in your own class that is a dll

Question

I am trying to write a class in a dll that uses a callback function from another dll. currently i can get the callback to work when i am calling it in a main function but i am having problems integrating it in my own dll.

I am using Hinstance in the regular project and the dll im compiling. This works in a regular project:

void mycallback(float values[], __int64 timestamp, int status) {
//stuff
 globalval[0]=values[0];
 ...
}

void main(){
 ...
 void(*_callback)(float[], __int64, int);
 _callback = &mycallback;
 API_CALLBACK finalCallBack = (API_CALLBACK)_callback;
....
//I pass this callback in another function that the api uses later
}

However this fails when I try to port it in the initialise function in a class that I am compiling as a dll (I was trying to use bind function but #include was giving me errors (using visual studios 2015)

void MyClass::mycallback(float values[], __int64 timestamp, int status){
//stuff
  myClassval[0]=values[0];
 ...
}

MyClass::Init(){
    void(*_callback)(float[], __int64, int);=
    _callback = &MyClass::mycallback;<---This line is giving me error
    API_CALLBACK finalCallBack = (API_CALLBACK)_callback;
  }

The error i get is "assigning to ' void(*)(float *,long long, int)' from incompaible type 'void(MyClass::*)(float *,long long,int)"

Is there a different way I should approach this? I am not sure how to handle this as I have only access to the function callbacks but not the source.

edit: I realise that casting mycallback as static would solve the problem but then I would run into the problem of being unable to store the value somewhere. or is there a good way to do this?

full code for further reference:

void main() {
    //declare dll handler
    HINSTANCE hinstLib;
    FCALL _InitDevices,_ReleaseDevices;
    FCALL_GETHMDINFO _getHMDinfo;
    FCALL_HMDPRESENT _HMDPresent;
    FCALL_STARTTRACKING _StartTracking;
    BOOL fFreeResult;
    //Load dll
    hinstLib = LoadLibrary(TEXT("thirdparty.dll"));

    bool* isHMDpresent = new bool;


    void(*_hmdcallback)(float[], __int64, int);
    _hmdcallback = &hmdcallback;
    HMD_TRACK_CALLBACK hmdCallBack = (HMD_TRACK_CALLBACK)_hmdcallback;


    //float handle = (float)hmdCallBack;
    //if dll present
    if (hinstLib != NULL)
    {
        //initialise devices
        _InitDevices = (FCALL)GetProcAddress(hinstLib, "InitDevices");

        if (NULL != _InitDevices)
        {
            std::cout<<(_InitDevices)()<<std::endl;
        }



        //start tracking
        _StartTracking = (FCALL_STARTTRACKING)GetProcAddress(hinstLib, "StartTracking");

        if (NULL != _StartTracking)
        {

            std::cout << (_StartTracking)(hmdCallBack,nullptr,nullptr,nullptr) << std::endl;


        }

this is the function from the 3rd party dll

DLL_EXPORT typedef void(__stdcall *HMD_TRACK_CALLBACK)(float values[], __int64 timestamp, int  status );

I am trying to convert the above and package it in another dll(a driver) with other functions from multiple dlls. The specific task i am trying to do now is to store an array from the callback of the dll i am using. In this case, one of the things im storing is values[]