C++ and SDL: How does SDL_Rect work exactly?

Question

I'm working on some SDL stuff and I've run into some trouble when trying to set the location of a loaded BMP.

Here's the code.

while(event.type != SDL_QUIT) //The game loop that does everything
{
    SDL_Rect *location;
    location = SDL_Rect(600,400,0,0);
    SDL_PollEvent(&event); //This "polls" the event
    //Drawing stuff goes here
    SDL_BlitSurface(zombie, NULL, buffer, &location);
    SDL_Flip(buffer); //Draw
}

It won't compile. What am I doing wrong?

Solution 1

SDL is written in C so SDL_Rect is just a simple struct.

To dynamically allocate it you'd have to use new otherwise the compiler will interpret your code as a call to a regular function called SDL_Rect that returns a SDL_Rect*.
In this case I see no reason to use dynamical allocation; just use the struct initialization syntax (and be careful of the declaration order of the struct's members):

SDL_Rect location = {0,0,600,400}; // or
SDL_Rect location{0,0,600,400}; // for C++11 & up (h/t @HolyBlackCat)

or explicitly initialize each of it's members (safer in case somebody decides to re-arange the order of the struct's members):

SDL_Rect location;
location.h = 600;
location.w = 400;
location.x = 0;
location.y = 0;

Solution 2

As an alternative to the above answer, if, for any reason, you did need to dynamically create location, you would need to do it like this:

while(event.type != SDL_QUIT) //The game loop that does everything
{
    SDL_Rect *location;
    location = new SDL_Rect(600,400,0,0);             //add new operator
    SDL_PollEvent(&event); //This "polls" the event
    //Drawing stuff goes here
    SDL_BlitSurface(zombie, NULL, buffer, location);
    SDL_Flip(buffer); //Draw
    delete location;                                  //IMPORTANT: deallocate memory
}

Note that, because an additional SDL_Rect will be created on each iteration of the loop, and there will cease to be a pointer to it on the next iteration, it is necessary to delete it before the end of the loop (in other words, to delete before the end of each iteration). Otherwise, you create a memory leak.

As an additional alternative, if you needed changes to location to persist from one iteration of your loop to the next, or if you didn't need to change within the loop at all, but you wanted to clean up your coda a little, you could do something like this:

SDL_Rect *location = new SDL_Rect(600,400,0,0);

while(event.type != SDL_QUIT) //The game loop that does everything
{
    SDL_PollEvent(&event); //This "polls" the event
    //Drawing stuff goes here
    SDL_BlitSurface(zombie, NULL, buffer, location);
    SDL_Flip(buffer); //Draw
}

delete location;

Comments

[Lemmons]

I didn't know it was written in C, thanks for telling me that and giving me a legit answer! :D

[HolyBlackCat]

By the way, since C++11 the first example can be rewritten as SDL_Rect location{0,0,600,400};