SDL

/*This source code copyrighted by Lazy Foo' Productions (2004-2019)
and may not be redistributed without written permission.*/
 
//Using SDL and standard IO
#include <SDL.h>
#include <stdio.h>
 
//Screen dimension constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
 
int main(int argc, char* args[])
{
    //The window we'll be rendering to
    SDL_Window* window = NULL;
 
    //The surface contained by the window
    SDL_Surface* screenSurface = NULL;
 
    //Initialize SDL
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        printf("SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
    }
    else
    {
        //Create window
        window = SDL_CreateWindow("SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
        if (window == NULL)
        {
            printf("Window could not be created! SDL_Error: %s\n", SDL_GetError());
        }
        else
        {
            //Get window surface
            screenSurface = SDL_GetWindowSurface(window);
 
            //Fill the surface white
            SDL_FillRect(screenSurface, NULL, SDL_MapRGB(screenSurface->format, 0xFF, 0xFF, 0xFF));
 
            //Update the surface
            SDL_UpdateWindowSurface(window);
 
            //Wait two seconds
            SDL_Delay(2000);
        }
    }
 
    //Destroy window
    SDL_DestroyWindow(window);
 
    //Quit SDL subsystems
    SDL_Quit();
 
    return 0;
}

...
SDL_Surface* screenSurface = NULL;
...
screenSurface = SDL_GetWindowSurface(window);
...
SDL_FillRect(screenSurface, NULL, SDL_MapRGB(screenSurface->format, 0xFF, 0xFF, 0xFF));
...

if(screenSurface == NULL) 
printf("It is not working SDL_Error: %s\n", SDL_GetError());