C++ class member variable resetting to 0 - class

Question

I'm trying to increment and decrement the index of a list of readings, however, everytime I run update(), m_notifIndex gets set back to zero. I'm sorry if this type of question has been asked before, but after looking for the answer for an hour, I gave up and went on to ask my first question here. Sorry for the bad formatting too, again, this is my first time posting.
Display.cpp
#include "display.h"
#include <time.h>
#include <unistd.h>
#include <iostream>
Display::Display(unsigned int width, unsigned int height, unsigned int num_sensors, std::string* sensors, const std::string& dir, Message* messages) {
m_notifIndex = 0;
}
void Display::update() {
if (m_showNotif) {
//when there are no more messages, show the notifications
while (!m_notifications->isEmpty()) {
//first draw the notification if there is a warning in the current index
if (m_notifications->sensors[m_notifIndex] != NULL) {
m_oled->clear(PAGE);
drawSensor();
m_oled->display();
sleep(1);
//keep updating the message and notif stack when there are no inputs
while (m_a->pinRead() == HIGH && m_right->pinRead() == HIGH && m_left->pinRead() == HIGH && m_b->pinRead() == HIGH) {
m_messages->updateMsgStack();
updateNotif();
if (!m_messages->isEmpty() || m_notifications->warnings[m_notifIndex])
return; //break away from the loop if a new message comes in
}
//listen in for inputs
if (m_right->pinRead() == LOW) {
//wait until the button is released
while (m_right->pinRead() == LOW) {}
if (m_notifIndex == m_num_sensors-1)
m_notifIndex = 0; //wrap around when at the end
else m_notifIndex++;
}
else if (m_left->pinRead() == LOW) {
while (m_left->pinRead() == LOW) {}
if (m_notifIndex == 0)
m_notifIndex = m_num_sensors-1; //wrap around when at the beginning
else m_notifIndex--;
}
else if (m_a->pinRead() == LOW) {
while (m_a->pinRead() == LOW) {}
m_showNotif = false;
return;
}
checkForPanic();
}
else { //when the current index has no warning
if (m_notifIndex == m_num_sensors-1)
m_notifIndex = 0; //wrap around when at the end
else m_notifIndex++;
}
}
}
}
void Display::updateNotif() {
std::string line;
for (unsigned int i = 0; i < sizeof(m_sensors)/sizeof(m_sensors[0]); i++) {
const char* filePath = (m_notifDir + m_sensors[i] + ".txt").c_str();
if (m_messages->exists(filePath)) {
usleep(10000);
try {
m_messages->m_incMsg.open(filePath);
while(std::getline(m_messages->m_incMsg, line)) {
m_notifications->addWarning (line, i);
}
m_messages->m_incMsg.close();
}
catch (std::ios_base::failure& e) {
std::cerr << e.what() << '\n' << std::endl;
}
}
else m_notifications->removeWarning (i); //delete the warning when the file doesnt exist
}
}
void Display::checkForPanic() {
if (m_b->pinRead() == LOW) {
time_t hold;
time(&hold);
while (m_b->pinRead() == LOW) {
if (time(NULL) > hold + 3) { //if the timer reaches 3 seconds
//m_messages->sendReply("Miner_Emergency");
return;
}
}
}
}
Display.h
#ifndef OLED_DISPLAY_H_
#define OLED_DISPLAY_H_
#include <sstream>
#include <string>
#include "image/image.h"
#include "oled/Edison_OLED.h"
#include "message.h"
#include "DataStructs/Notif.h"
#include "gpio/gpio.h"
#define SLEEPTIMEOUT 20
class Display {
public:
Display(unsigned int width, unsigned int height, unsigned int num_sensors, std::string* sensors, const std::string& dir, Message* messages);
void run();
~Display();
private:
edOLED* m_oled;
const unsigned int m_height, m_width;
Image* m_miner;
Image* m_checkin;
Image* m_reminder;
Image* m_blast;
Image* m_go_to;
Image* m_goto_zone;
bool m_isSleeping, m_showNotif;
time_t m_timer;
Message* m_messages;
std::string* m_sensors;
std::string m_notifDir;
NotifHandler* m_notifications;
unsigned int m_notifIndex;
const unsigned int m_num_sensors;
gpio* m_up;
gpio* m_down;
gpio* m_left;
gpio* m_right;
gpio* m_a;
gpio* m_b;
void drawImage(Image* image);
void update();
void drawMessage(MsgNode* message);
void drawTime();
void drawSensor();
void updateNotif();
void checkForPanic();
};
#endif //OLED_DISPLAY_H_