Exception thrown: write access violation. this->**m_buffer** was 0x1110112. occurred

I am getting this access violation. I use SDL2 obviously. I tried to access the pixel in the middle of the screen and set that one to white. I have tried to use other than Uint32but that did not help. Maybe something is wrong with the order of colours in void Screen::setPixel (int x, int y, Uint8 red, Uint8 green, Uint8 blue) ?

Class:

#include "Screen.h"

namespace SebProj {

Screen::Screen() : m_window(NULL), m_renderer(NULL), m_texture(NULL), m_buffer(NULL) {

    }

bool Screen::init() {
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        std::cout << "SDL Init failed" << std::endl;
        return false;
    }

    m_window = SDL_CreateWindow("Particle Fire Explosion", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGTH, SDL_WINDOW_SHOWN);

    if (m_window == NULL) {
        SDL_Quit();
        return false;
    }

    m_renderer = SDL_CreateRenderer(m_window, -1, SDL_RENDERER_PRESENTVSYNC);
    m_texture = SDL_CreateTexture(m_renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STATIC, SCREEN_WIDTH, SCREEN_HEIGTH);

    if (m_renderer == NULL) {
        std::cout << "Could nor create renderer" << std::endl;
        SDL_DestroyWindow(m_window);
        SDL_Quit();
        return false;
    }

    if (m_texture == NULL) {
        std::cout << "Could not create texture" << std::endl;
        SDL_DestroyRenderer(m_renderer);
        SDL_DestroyWindow(m_window);
        SDL_Quit();
        return false;
    }

    Uint32* buffer = new Uint32[SCREEN_WIDTH * SCREEN_HEIGTH];

    memset(buffer, 0, SCREEN_WIDTH * SCREEN_HEIGTH * sizeof(Uint32)); // memset: Set a block of memory with a particular value

    // buffer[30000] = 0xFFFFFFFF; (is changing a single pixel

    for (int i = 0; i < SCREEN_WIDTH * SCREEN_HEIGTH; i++) {
        buffer[i] = 0xFF; // 0x0000FFFF: hexadecimal, because you only need two digits to specify one single byte
    }

    return true;
    }

void Screen::setPixel(int x, int y, Uint8 red, Uint8 green, Uint8 blue) {

    Uint32 colour = 0;

    colour += red;
    colour <<= 8;
    colour += green;
    colour <<= 8;
    colour += blue;
    colour <<= 8;
    colour += 0xFF;

    m_buffer[(y * SCREEN_WIDTH) + x] = colour;
}

void Screen::update() {
    SDL_UpdateTexture(m_texture, NULL, m_buffer, SCREEN_WIDTH * sizeof(Uint32));
    SDL_RenderClear(m_renderer);
    SDL_RenderCopy(m_renderer, m_texture, NULL, NULL);
    SDL_RenderPresent(m_renderer);
}

bool Screen::processEvents() {
    SDL_Event event;

    while (SDL_PollEvent(&event)) {
        if (event.type == SDL_QUIT) {
            return false;
        }
    }

    return true;
    }

void Screen:: close() {
    delete[] m_buffer;
    SDL_DestroyRenderer(m_renderer);
    SDL_DestroyTexture(m_texture);
    SDL_DestroyWindow(m_window);
    SDL_Quit();
    }
}

Main source file:

// Red: 0x00ff0000
// Green: 0x0000ff00
// Blue: 0x000000ff
// Yellow: 0x00ffff00

#include "Screen.h" // Brings <iostream> and "SDL.h"
#undef main

int main()
{
    SebProj::Screen screen; // Or "using namespace SebProj" before the main function

    if(!screen.init()) {
        std::cout << "Error initialising SDL." << std::endl;
    }

    int max = 0;

    while (true) {
        // Draw Particles

        // Update Particles
        for (int y = 0; y < SebProj::Screen::SCREEN_HEIGTH; y++) {
            for (int x = 0; x < SebProj::Screen::SCREEN_WIDTH; x++) {
                screen.setPixel(x, y, 128, 0, 255);
            }
        }

        screen.setPixel(400, 300, 255, 255, 255);

        // Draw the screen
        screen.update();

        // Check for messages/events
        if(screen.processEvents() == false) {
            break;
        }
    }

    screen.close();

    return 0;
}