Global Access to a Singleton's Data - c++

Question

So I'm making a graphical application (game) that I want to utilize an Asset Manager. For this class I decided to use a Singleton Design. So in my main.cpp I would load something like...
ASSET_MANAGER.LoadImage("res/graphics/background.png", "background");
Here is the implication of the macros/methods used in the line above. This is sort of a mashup of code that I have to make things simpler to look at instead of pasting a few hundred lines of code into here.
assetmanager.h
#define ASSET_MANAGER AssetManager::GetAssetManager()
#define DEBUG
class AssetManager {
public:
static AssetManager &GetAssetManager();
//-----------------------------------------------------------------------------
// Purpose: Load a new image for the game to use. This function will store an
// instance of the asset in memory (in a hash map corresponding with
// the data type provided.
//
// param file: The location on disk of the asset
// param key: The string you use to receive this asset (defaults to the path str)
//-----------------------------------------------------------------------------
bool LoadImage(const char *file, const char *key = "");
//-----------------------------------------------------------------------------
// Purpose: Returns the image
//
// param key: The string used to store the asset in memory
//-----------------------------------------------------------------------------
ALLEGRO_BITMAP *GetImage(const char *key);
//-----------------------------------------------------------------------------
// Purpose: Destroys an asset that is presumably no longer needed by the game.
// This function is good for performance so that you don't use more
// RAM than you need to.
//
// param key: The string you use to receive this asset (defaults to the path str)
//-----------------------------------------------------------------------------
void DiscardImage(const char *key);
private:
AssetManager();
~AssetManager();
std::map<const char *, std::shared_ptr<ALLEGRO_BITMAP>> _ImageMap;
}
assetmanager.cpp
AssetManager &AssetManager::GetAssetManager() {
static AssetManager instance;
return instance;
}
bool AssetManager::LoadImage(const char *file, const char *key) {
key = key == "" ? file : key;
std::shared_ptr<ALLEGRO_BITMAP> x(al_load_bitmap(file), al_destroy_bitmap);
if (!x) {
fprintf(stderr, "Failed to load %s\n", file);
return false;
}
#ifdef DEBUG
printf("DEBUG: Loaded %s\n", key); //debug
#endif // DEBUG
_ImageMap.insert(std::pair<const char *, std::shared_ptr<ALLEGRO_BITMAP>>(key, x));
return true;
}
ALLEGRO_BITMAP *AssetManager::GetImage(const char *key) {
return _ImageMap.find(key) != _ImageMap.end() ? _ImageMap.at(key).get() : nullptr;
}
void AssetManager::DiscardImage(const char *key) {
_ImageMap.erase(key);
#ifdef DEBUG
printf("DEBUG: Discarded %s\n", key); //debug
#endif // DEBUG
}
This class only works from the class I initialized the asset manager in while I expected it to work anywhere that I called ASSET_MANAGER. It compiles fine, it only crashes when I try to use the manager in a different class and pass it into an allegro function because it returns something that is null instead of the proper allegro data types. What don't I understand about this?

Answer 1

The Char* in the map stores the location and not the data which makes the program think it's null.