The Singleton design pattern
Hy there, here’s a singleton class(SoundManager). Using a singleton design pattern is very useful, at least that’s what i use in game developement. This design pattern make your life easy beacause it has only one instance.. again .. ONLY ONE :) threfore you can call the static member function getInstance() to obtain the single instance of the class from anywhere in the code … enaugh said .. the rest is code 
made just to prove the singleton pattern
#include <iostream>
using namespace std;
class Sound{};
class SoundManager
{
static SoundManager * instance;
static int numberOfInstances;
Sound * sounds;
int numberOfSounds;
SoundManager()
{
sounds = new Sound[]; // DYNAMIC ARRAY OF SOUNDS
numberOfSounds = 0;
};
public:
~SoundManager(){ numberOfInstances — ; /*IF WE DESTROY A REFERENCE TO THE SINGLETON WITH delete() WE MUST DECREMENT THE NUMBER OF REFERENCE */};
static SoundManager * getInstance();
void addSound(Sound sound);
int howManySounds();
int howManyInstances();
};
int SoundManager::numberOfInstances = 0; // INITIALIZE THE NUMBER OF INSTANCES WITH 0
SoundManager* SoundManager::instance = NULL; // MAKE THE INITIAL INSTANCE NULL
SoundManager * SoundManager::getInstance()
{
if(numberOfInstances == 0) // IF THE NUMBER OF REFS IS 0 (NONE HAS BEEN MADE YET) …
instance = new SoundManager(); // WE SHOULD MAKE A NEW ONE … RIGHT ?
numberOfInstances ++ ; // INCREMENT THE REFS COUNTER
return instance;
}
// .. THE REST IS HISTORY
void SoundManager::addSound(Sound sound)
{
cout << ” – added sound – ” << endl;
sounds[numberOfSounds++] = sound;
}
int SoundManager::howManySounds()
{
return numberOfSounds;
}
int SoundManager::howManyInstances()
{
return numberOfInstances;
}
int main()
{
SoundManager *s1, *s2;
Sound s,a,b,c;
s1 = SoundManager::getInstance();
s2 = SoundManager::getInstance();
s1->addSound(s);
s1->addSound(a);
s1->addSound(b);
s1->addSound(c);
cout << ” No instances : ” << s1->howManyInstances() << endl; // WE NOW HAVE JUST 2 POINTERS TO THE OBJECT BUT ONLY ONE OBJECT
cout << ” No sounds : ” << s2->howManySounds() << endl; // WE HAVE 4 SOUNDS
cout << ” No sounds : ” << s1->howManySounds() << endl; // STIL 4 SOUNDS BEACAUSE THE S1 POINTS AT THE SAME INSTANCE AS S2
// LET’S MAKE ANOTHER POINTER AT THE SINGLETON CLASS… BUT NOT A NEW OBJECT …
SoundManager *lastInstance = SoundManager::getInstance();
cout << ” No sounds : ” << lastInstance->howManySounds() << endl; // YEP STIL 4 SOUNDS
cout << ” No instances : ” << lastInstance->howManyInstances() << endl;
return 0;
}
