in one file

application.cpp

#include "application.h"

SYSTEM_THREAD(ENABLED);

class WiFiManager {

	public:

		WiFiManager();
		virtual ~WiFiManager();

		void setup();
		void loop();

		static void handle_ap(WiFiAccessPoint* wap, WiFiManager* self);
		void next(WiFiAccessPoint& ap);
};


WiFiManager::WiFiManager() {
}

WiFiManager::~WiFiManager() {
}//

void WiFiManager::setup() {
	//Serial.println("hi");
}

void WiFiManager::loop() {
	//delay(1000);
  WiFi.scan(handle_ap, this);
	//bool check = isStoredSSIDAvailable();
	//if(check) Serial.println("checked");
	delay(1000);

}

// This is the callback passed to WiFi.scan()
// It makes the call on the `self` instance - to go from a static
// member function to an instance member function.
void WiFiManager::handle_ap(WiFiAccessPoint* wap, WiFiManager* self)
{
	 self->next(*wap);
}

void WiFiManager::next(WiFiAccessPoint& ap)
{
	Serial.print("SSID: ");
	Serial.println(ap.ssid);
}

WiFiManager wifiManager;

void setup() {

  Serial.begin(57600);

  wifiManager.setup();

  // adding a delay to the end of setup solves the crash.
  delay(800);
}

void loop() {
  wifiManager.loop();
}