Simple dl example using SDL2 on Linux

main.c

// $ cc -o main main.c -ldl
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#include <dlfcn.h>

#define SDL_LIBRARY_NAME "libSDL2-2.0.so"
#define SDL_INIT_VIDEO 0x00000020u
#define SDL_WINDOW_RESIZABLE 0x00000020
#define SDL_RENDERER_ACCELERATED 0x00000002
#define SDL_QUIT 0x100

typedef void SDL_Window;
typedef void SDL_Renderer;

typedef union SDL_Event {
    uint32_t type;
    uint8_t padding[56];
} SDL_Event;

int (*SDL_Init)(uint32_t flags) = NULL;
const char *(*SDL_GetError)(void) = NULL;
void (*SDL_Quit)(void) = NULL;
SDL_Window *(*SDL_CreateWindow)(const char *title,
                                int x, int y, int w,
                                int h, uint32_t flags) = NULL;
SDL_Renderer *(*SDL_CreateRenderer)(SDL_Window * window,
                                    int index, uint32_t flags) = NULL;
int (*SDL_PollEvent)(SDL_Event *event) = NULL;
int (*SDL_SetRenderDrawColor)(SDL_Renderer* renderer, uint8_t r, uint8_t g, uint8_t b, uint8_t a) = NULL;
int (*SDL_RenderClear)(SDL_Renderer* renderer) = NULL;
void (*SDL_RenderPresent)(SDL_Renderer* renderer) = NULL;

void *load_symbol(void *handle, const char *name)
{
    void *result = dlsym(handle, name);
    if (result == NULL) {
        fprintf(stderr, "ERROR: could not find symbol %s: %s\n",
                name, dlerror());
        exit(1);
    }

    printf("Successfully found symbol %s: %p\n", name, (void*)result);
    return result;
}

void load_sdl(void *handle)
{
    SDL_Init = load_symbol(handle, "SDL_Init");
    SDL_GetError = load_symbol(handle, "SDL_GetError");
    SDL_Quit = load_symbol(handle, "SDL_Quit");
    SDL_CreateWindow = load_symbol(handle, "SDL_CreateWindow");
    SDL_CreateRenderer = load_symbol(handle, "SDL_CreateRenderer");
    SDL_PollEvent = load_symbol(handle, "SDL_PollEvent");
    SDL_SetRenderDrawColor = load_symbol(handle, "SDL_SetRenderDrawColor");
    SDL_RenderClear = load_symbol(handle, "SDL_RenderClear");
    SDL_RenderPresent = load_symbol(handle, "SDL_RenderPresent");
}

int main(void)
{
    void *sdl_lib = dlopen(SDL_LIBRARY_NAME, RTLD_LAZY);
    if (sdl_lib == NULL) {
        fprintf(stderr, "ERROR: could not load library `"SDL_LIBRARY_NAME"`: %s\n",
                dlerror());
        exit(1);
    }

    printf("Successfully loaded library `"SDL_LIBRARY_NAME"`\n");

    load_sdl(sdl_lib);

    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        fprintf(stderr, "ERROR: could not initialize SDL: %s\n", SDL_GetError());
        exit(1);
    }


    SDL_Window *window = SDL_CreateWindow(
                             "Khello",
                             0, 0, 800,
                             600, SDL_WINDOW_RESIZABLE);
    if (window == NULL) {
        fprintf(stderr, "ERROR: could not create SDL window: %s\n", SDL_GetError());
        exit(1);
    }


    SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
    if (renderer == NULL) {
        fprintf(stderr, "ERROR: could not create SDL renderer: %s\n", SDL_GetError());
        exit(1);
    }

    int quit = 0;
    while (!quit) {
        SDL_Event event = {0};
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = 1;
            }
        }

        SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
        SDL_RenderClear(renderer);

        SDL_RenderPresent(renderer);
    }

    SDL_Quit();

    if (dlclose(sdl_lib) != 0) {
        fprintf(stderr, "ERROR: could not close library `"SDL_LIBRARY_NAME"`: %s\n",
                dlerror());
        exit(1);
    }

    printf("Successfully closed library `"SDL_LIBRARY_NAME"`\n");

    return 0;
}