Put Coap Works in another class - c++

Question

I've used coap server like this :
coapServer coap;
coap.server(callback_light, "light");
coap.start();
And the callback method :
void callback_light(coapPacket *packet, IPAddress ip, int port,int obs) {
///Some Work...
}
and it works perfectly.
I've made a class called COAPService and the header file :
#include <coap_server.h>
class COAPService
{
private:
coapServer coap;
int WiFiTimeOut = 5000;
void getListOfWiFi(coapPacket *packet, IPAddress ip, int port, int obs);//id = 0 GET
public:
COAPService();
void COAPLoop();
};
and the cpp file :
#include "COAPService.h"
#include <coap_server.h>
#include <ESP8266WiFi.h>
COAPService::COAPService()
{
coap.server(static_cast<COAPService*>(this)->getListOfWiFi, "wifilist");
coap.start(5683);
}
void COAPService::getListOfWiFi(coapPacket *packet, IPAddress ip, int port, int obs) //id = 0 GET
{
///Some Work
}
My problem is in the constructor.
when i call static_cast(this)->getListOfWiFi for a callBack method it returns :
COAPService.cpp:7:75: error: no matching function for call to 'coapServer::server(<unresolved overloaded function type>, const char [9])'
coap.server(static_cast<COAPService*>(this)->getListOfWiFi, "wifilist");
Why this error appears ?

Answer 1

I assume the problem is that you are passing a member function pointer to coapServer in order to be called at some point in the future.
If this is right, I assume that the function pointer you pass as argument to coap.server() must be a non-member function as you didn't pass the object pointer any time.
Try to transform getListOfWiFi in a static one (include the keyword static in the function signature):
static void getListOfWiFi(coapPacket *packet, IPAddress ip, int port, int obs);
Or just declare this function outside of any class/struct.
And in the COAPService ctor, just pass its address:
COAPService::COAPService()
{
// the static_cast you made here doesn't make much sense.
coap.server(getListOfWiFi, "wifilist");
coap.start(5683);
}