Help: calling wifi class from a 2nd cpp file

2

You can declare your wifiMulti object in a header file as an extern object, thus allowing other .cpp files to see your global variable you defined in another cpp file.

For example, create a wifi.h with the contents

#ifndef OWN_WIFI_H
#define OWN_WIFI_H

#include <ESP8266WiFiMulti.h>
extern ESP8266WiFiMulti wifiMulti;

#endif

You may then #include "wifi.h" in your mqtt.cpp and have full access over to your wifiMulti variable, which was defined in wifi.cpp.