Elementary inquiry about C++ (SDL2 library) - c++

Question

I'm fairly new to programming, so this question will probably be basic. I'm writing a very basic program in C++ with the SDL2 library (in Visual Studio 2013). When I was writing it, I came across a problem. I wrote the following:
int controles(){
//declare actions that will happen when a key is pressed
const Uint8 * estado = SDL_GetKeyboardState(NULL);
if (estado[SDL_SCANCODE_UP]){ y--; SDL_UpdateWindowSurface(ventana); }
if (estado[SDL_SCANCODE_DOWN]){ y++; SDL_UpdateWindowSurface(ventana); }
return 0;
}
The problem is that I need to update the window surface after the value of y is modified, but I get an error because ventana, the name of the window, is defined in another function. I tried to define ventana globally, but the program won't work then. I then thought the following; write a goto statement in graficos, the function where ventana is defined, in order to skip every other statement in that function, except for the one that updates the window surface. However, when I did that, the program doesn't even compile:
int graficos(int caso){
if (caso == 1) {goto reload;} //skip to reload if (1)
SDL_Init(SDL_INIT_VIDEO); //load SDL
//load graphics in memory
SDL_Window * ventana = SDL_CreateWindow("ventana", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);
SDL_Surface * superficie = SDL_GetWindowSurface(ventana);
SDL_Surface * pantallainicio = SDL_LoadBMP("pantallainicio.bmp");
SDL_Surface * paleta = SDL_LoadBMP("paleta.bmp");
SDL_Rect rpantallainicio = { 0, 0, 640, 480 };
SDL_Rect rpaleta = { x, y, 16, 16 };
//render graphics
SDL_BlitSurface(pantallainicio, NULL, superficie, &rpantallainicio);
SDL_BlitSurface(paleta, NULL, superficie, &rpaleta);
SDL_UpdateWindowSurface(ventana);
reload:SDL_UpdateWindowSurface(ventana);
return 0;
}
I get the following errors:
error C4533: initialization of 'rpaleta' is skipped by 'goto reload'
error C4533: initialization of 'rpantallainicio' is skipped by 'goto reload'
I hope I explained my issue well enough. What can I do? Is there a way to fix this? Or can I reference ventana in some other way? This issue might be very basic, sorry for that, and thanks in advance!

Answer 1

You can fix this issue by simply not using goto at all - use a sub-function instead. Also, extract the variable ventana, as you need it to be stored and usable by graficos whenever.
void init()
{
SDL_Init(SDL_INIT_VIDEO); //load SDL
//load graphics in memory
ventana = SDL_CreateWindow("ventana", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);
SDL_Surface * superficie = SDL_GetWindowSurface(ventana);
SDL_Surface * pantallainicio = SDL_LoadBMP("pantallainicio.bmp");
SDL_Surface * paleta = SDL_LoadBMP("paleta.bmp");
SDL_Rect rpantallainicio = { 0, 0, 640, 480 };
SDL_Rect rpaleta = { x, y, 16, 16 };
//render graphics
SDL_BlitSurface(pantallainicio, NULL, superficie, &rpantallainicio);
SDL_BlitSurface(paleta, NULL, superficie, &rpaleta);
}
int graficos(int caso)
{
if (caso != 1) { init(); } //skip to reload if (1)
SDL_UpdateWindowSurface(ventana);
return 0;
}
SDL_Window * ventana;
Use of goto should generally be avoided. Use subroutines or other alternatives where possible. Here, the code does exactly the same thing as originally intended, but the "extra" flow that occurs when caso is not 1 is wrapped in its own subroutine named 'init'.