int SDL_GL_SetAttribute(SDL_GLattr attr,
                        int        value)

SDL_Window *window;
SDL_GLContext context;

SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

window = SDL_CreateWindow("OpenGL Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_OPENGL);
if (!window)
{
    fprintf(stderr, "Couldn't create window: %s\n", SDL_GetError());
    return;
}

context = SDL_GL_CreateContext(window);
if (!context)
{
    fprintf(stderr, "Couldn't create context: %s\n", SDL_GetError());
    return;
}

int r, g, b;
SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &r);
SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE, &g);
SDL_GL_GetAttribute(SDL_GL_BLUE_SIZE, &b);

printf("Red size: %d, Green size: %d, Blue size: %d\n", r, g, b);