instance changes in constructor and .cpp file for SoundManager

include/SoundManager.h

@@ -23,7 +23,12 @@ class SoundManager
 	public:
 
 		SoundManager() {
-			this_instance = this;
+			if (this_instance == nullptr) {
+				this_instance = this;
+			}
+			else {
+				throw std::runtime_error("SoundManager instance already exists!");
+			}
 		}
 		~SoundManager() {
 			for (auto& it : this->sound_cache) {
@@ -81,6 +86,10 @@ class SoundManager
 		static void addSingleBackgroundMusic(BackgroundMusic backgroundMusic, const char* path);
 		static void addBackgroundMusic(const std::map<BackgroundMusic, const char*> &backgroundMusic);
 
+		static SoundManager* getInstance() {
+			return this_instance;
+		}
+
 
 	private:
 

src/SoundManager.cpp

@@ -185,6 +185,8 @@ void SoundManager::addBackgroundMusic(const std::map<BackgroundMusic, const char
 		addSingleBackgroundMusic(track.first, track.second);
 }
 
+SoundManager* SoundManager::this_instance = nullptr;
+