std::string imagePath = ".../sdl2_test/hello.bmp"; // Указал полный путь
SDL_Surface *bmp = SDL_LoadBMP(imagePath.c_str());
if(bmp == 0){
SDL_DestroyWindow(win);
SDL_DestroyRenderer(ren);
std::cout << "SDL_LoadBMP Error: " << SDL_GetError() << std::endl;
SDL_Quit();
return 4;
}