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C++ Singleton design pattern

Recently I've bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real-life example):

// a lot of methods are omitted here
class Singleton
{
   public:
       static Singleton* getInstance( );
       ~Singleton( );
   private:
       Singleton( );
       static Singleton* instance;
};

From this declaration, I can deduce that the instance field is initiated on the heap. That means there is a memory allocation. What is completely unclear for me is when exactly the memory is going to be deallocated? Or is there a bug and memory leak? It seems like there is a problem with the implementation.

My main question is, how do I implement it in the right way?

You'll find a great discussion of how to implement a singleton, along with thread-safety in C++ in this paper. aristeia.com/Papers/DDJ%5FJul%5FAug%5F2004%5Frevised.pdf
@sbi - Only a Sith deals in absolutes. Can the vast majority of problems be solved without Singletons? Absolutely. Do Singletons cause problems of their own? Yes. However, I can't honestly say that they're bad, since design is all about considering the tradeoffs and understanding the nuances of your approach.
@derekerdmann: I didn't say you never need a global variable (and when you need one, a Singleton sometimes is better). What I said is that they should be used as little as possible. Glorifying Singleton as a valuable design pattern gives the impression it's good to use it, rather than that it is a hack, making code hard to understand, hard to maintain, and hard to test. This is why I posted my comment. None of what you said so far contradicted this.
@sbi: What you said was "Don't use them." Not the much more reasonable "they should be used as little as possible" you later changed to - surely you see the difference.

S
ShadowRanger

In 2008 I provided a C++98 implementation of the Singleton design pattern that is lazy-evaluated, guaranteed-destruction, not-technically-thread-safe:
Can any one provide me a sample of Singleton in c++?

Here is an updated C++11 implementation of the Singleton design pattern that is lazy-evaluated, correctly-destroyed, and thread-safe.

class S
{
    public:
        static S& getInstance()
        {
            static S    instance; // Guaranteed to be destroyed.
                                  // Instantiated on first use.
            return instance;
        }
    private:
        S() {}                    // Constructor? (the {} brackets) are needed here.

        // C++ 03
        // ========
        // Don't forget to declare these two. You want to make sure they
        // are inaccessible(especially from outside), otherwise, you may accidentally get copies of
        // your singleton appearing.
        S(S const&);              // Don't Implement
        void operator=(S const&); // Don't implement

        // C++ 11
        // =======
        // We can use the better technique of deleting the methods
        // we don't want.
    public:
        S(S const&)               = delete;
        void operator=(S const&)  = delete;

        // Note: Scott Meyers mentions in his Effective Modern
        //       C++ book, that deleted functions should generally
        //       be public as it results in better error messages
        //       due to the compilers behavior to check accessibility
        //       before deleted status
};

See this article about when to use a singleton: (not often)
Singleton: How should it be used

See this two article about initialization order and how to cope:
Static variables initialisation order
Finding C++ static initialization order problems

See this article describing lifetimes:
What is the lifetime of a static variable in a C++ function?

See this article that discusses some threading implications to singletons:
Singleton instance declared as static variable of GetInstance method, is it thread-safe?

See this article that explains why double checked locking will not work on C++:
What are all the common undefined behaviours that a C++ programmer should know about?
Dr Dobbs: C++ and The Perils of Double-Checked Locking: Part I


Good answer. But should note that this is not thread-safe stackoverflow.com/questions/1661529/…
Already noted above in: stackoverflow.com/questions/449436/…
@zourtney: Many people don't realize what you just did :)
@MaximYegorushkin: When this is destroyed is very well defined (there is no ambiguity). See: stackoverflow.com/questions/246564/…
What irks me most though is the run-time check of the hidden boolean in getInstance() That is an assumption on implementation technique. There need be no assumptions about it being alive. see stackoverflow.com/a/335746/14065 You can force a situation so that it is always alive (less overhead than Schwarz counter). Global variables have more issues with initialization order (across compilation units) as you not force an order. The advantage of this model is 1) lazy initialization. 2) Ability to enforce an order (Schwarz helps but is uglier). Yep get_instance() is much uglier.
C
Cătălin Pitiș

You could avoid memory allocation. There are many variants, all having problems in case of multithreading environment.

I prefer this kind of implementation (actually, it is not correctly said I prefer, because I avoid singletons as much as possible):

class Singleton
{
private:
   Singleton();

public:
   static Singleton& instance()
   {
      static Singleton INSTANCE;
      return INSTANCE;
   }
};

It has no dynamic memory allocation.


In some instances, this lazy initialization is not the ideal pattern to follow. One example is if the constructor of the singleton allocates memory from the heap and you wish that allocation to be predictable, for instance in an embedded system or other tightly controlled environment. I prefer, when the Singleton pattern is the best pattern to use, to create the instance as a static member of the class.
For many larger programs, especially those with dynamic libraries. Any global or static object that's none primitive can lead to segfaults/crashes upon program exit on many platforms due to order of destruction issues upon libraries unloading. This is one of the reasons many coding conventions (including Google's) ban the use of non-trivial static and global objects.
It seems that the static instance in such implementation has internal linkage, and will have unique and independent copies in different translation unit, which will cause confusing and wrong behavior. But I saw many such implementation, am I missing something?
What prevents user from assigning this to multiple objects where compiler behind the scenes uses its own copy constructor?
@FaceBro There are two instances of the keyword static here, but neither of them is problematic from the standpoint of linkage. The first appearance of static is about static member functions, which is nothing to do with linkage. The second appearance of static is about the storage duration of INSTANCE. The object will live in memory for the duration of the program, and it doesn't matter that you cannot access it by name outside of the TU because you access it via the member function instance, which has external linkage.
R
Reed Copsey

Being a Singleton, you usually do not want it to be destructed.

It will get torn down and deallocated when the program terminates, which is the normal, desired behavior for a singleton. If you want to be able to explicitly clean it, it's fairly easy to add a static method to the class that allows you to restore it to a clean state, and have it reallocate next time it's used, but that's outside of the scope of a "classic" singleton.


It's not a memory leak anymore than a simple declaration of a global variable.
To set something straight... "memory leak" concerns vis-a-vis singletons are completely irrelevent. If you have stateful resources in which deconstruction order matters, singletons can be dangerous; but all of the memory is cleanly regained by the operating system on program termination... nullifying this totally academic point in 99.9% of cases. If you want to argue the grammar back and forth of what is and is not a "memory leak", that's fine, but realize that it's a distraction from actual design decisions.
@jkerian: Memory leaks and destruction in the C++ context is not really about the memory leaking. Really it is about resource control. If you leak memory the destroctor is not called and thus any resources associated with the object are not correctly released. Memory is just the simple example we use when teaching programming but there are much more complex resources out there.
@Martin I agree with you completely. Even if the only resource is memory, you will still get into trouble trying to find REAL leaks in your program if you have to wade through a list of leaks, filtering out ones that "don't matter." It is better to clean these all up so any tool that reports leaks only reports things that ARE a problem.
It's vaguely worth considering that there exist C++ implementations (potentially even hosted ones) in which the "OS" does not recover all resources when your program exits, but which do have some concept of "running your program again" which gives you a fresh set of globals and static locals. On such systems an unfreed singleton is a genuine leak by any sensible definition: if your program is run enough times it will take down the system. Whether you care about portability to such systems is another matter -- as long as you aren't writing a library you almost certainly don't.
C
Community

@Loki Astari's answer is excellent.

However there are times with multiple static objects where you need to be able to guarantee that the singleton will not be destroyed until all your static objects that use the singleton no longer need it.

In this case std::shared_ptr can be used to keep the singleton alive for all users even when the static destructors are being called at the end of the program:

class Singleton
{
public:
    Singleton(Singleton const&) = delete;
    Singleton& operator=(Singleton const&) = delete;

    static std::shared_ptr<Singleton> instance()
    {
        static std::shared_ptr<Singleton> s{new Singleton};
        return s;
    }

private:
    Singleton() {}
};

Could you explain the two lines with = delete, as a C# programmer, this syntax looks a bit weird to me. Or could you provide a link where I can read about this exact syntax?
@MohammedNoureldin By default C++ will automatically generate functions to make copies of an object. If you want to prevent your objects from being copied you can "delete" those function. So = delete tells the compiler not to generate them.
Does this achieve the Nifty Counter pattern mentioned in the unfinished faq isocpp.org/wiki/faq/ctors#nifty-counter-idiom?
@RexYuan Yes, I believe so. It will make sure your singleton object is not destroyed until after the very last component that needs it has been destroyed first. But you need to make sure that the singleton itself does not require any global static objects during its destruction and as long as you haven't done anything daft like keeping a raw-pointer or a raw reference to its target object outside of the std::shared_ptr.
J
James Hopkin

Another non-allocating alternative: create a singleton, say of class C, as you need it:

singleton<C>()

using

template <class X>
X& singleton()
{
    static X x;
    return x;
}

Neither this nor Cătălin's answer is automatically thread-safe in current C++, but will be in C++0x.


Currently under gcc it is thread safe (and has been for a while).
The problem with this design is that if used across multiple libraries. Each library has is own copy of the singleton that that library uses. So it is no longer a singleton.
Y
Yuriy

I did not find a CRTP implementation among the answers, so here it is:

template<typename HeirT>
class Singleton
{
public:
    Singleton() = delete;

    Singleton(const Singleton &) = delete;

    Singleton &operator=(const Singleton &) = delete;

    static HeirT &instance()
    {
        static HeirT instance;
        return instance;
    }
};

To use just inherit your class from this, like: class Test : public Singleton<Test>


Could not get this to work with C++17 until I made default constructor protected and '= default;'.
T
Tony Bai

We went over this topic recently in my EECS class. If you want to look at the lecture notes in detail, visit http://umich.edu/~eecs381/lecture/IdiomsDesPattsCreational.pdf. These notes (and quotations I give in this answer) were created by my Professor, David Kieras.

There are two ways that I know to create a Singleton class correctly.

First Way:

Implement it similar to the way you have it in your example. As for destruction, "Singletons usually endure for the length of the program run; most OSs will recover memory and most other resources when a program terminates, so there is an argument for not worrying about this."

However, it is good practice to clean up at program termination. Therefore, you can do this with an auxiliary static SingletonDestructor class and declare that as a friend in your Singleton.

class Singleton {
public:
  static Singleton* get_instance();
  
  // disable copy/move -- this is a Singleton
  Singleton(const Singleton&) = delete;
  Singleton(Singleton&&) = delete;
  Singleton& operator=(const Singleton&) = delete;
  Singleton& operator=(Singleton&&) = delete;

  friend class Singleton_destroyer;

private:
  Singleton();  // no one else can create one
  ~Singleton(); // prevent accidental deletion

  static Singleton* ptr;
};

// auxiliary static object for destroying the memory of Singleton
class Singleton_destroyer {
public:
  ~Singleton_destroyer { delete Singleton::ptr; }
};

// somewhere in code (Singleton.cpp is probably the best place) 
// create a global static Singleton_destroyer object
Singleton_destoyer the_destroyer;

The Singleton_destroyer will be created on program startup, and "when program terminates, all global/static objects are destroyed by the runtime library shutdown code (inserted by the linker), so the_destroyer will be destroyed; its destructor will delete the Singleton, running its destructor."

Second Way

This is called the Meyers Singleton, created by C++ wizard Scott Meyers. Simply define get_instance() differently. Now you can also get rid of the pointer member variable.

// public member function
static Singleton& Singleton::get_instance()
{
  static Singleton s;
  return s;
}

This is neat because the value returned is by reference and you can use . syntax instead of -> to access member variables.

"Compiler automatically builds code that creates 's' first time through the declaration, not thereafter, and then deletes the static object at program termination."

Note also that with the Meyers Singleton you "can get into very difficult situation if objects rely on each other at the time of termination - when does the Singleton disappear relative to other objects? But for simple applications, this works fine."


L
LastBlow

Here is an easy implementation.

#include <Windows.h>
#include <iostream>

using namespace std;


class SingletonClass {

public:
    static SingletonClass* getInstance() {

    return (!m_instanceSingleton) ?
        m_instanceSingleton = new SingletonClass : 
        m_instanceSingleton;
    }

private:
    // private constructor and destructor
    SingletonClass() { cout << "SingletonClass instance created!\n"; }
    ~SingletonClass() {}

    // private copy constructor and assignment operator
    SingletonClass(const SingletonClass&);
    SingletonClass& operator=(const SingletonClass&);

    static SingletonClass *m_instanceSingleton;
};

SingletonClass* SingletonClass::m_instanceSingleton = nullptr;



int main(int argc, const char * argv[]) {

    SingletonClass *singleton;
    singleton = singleton->getInstance();
    cout << singleton << endl;

    // Another object gets the reference of the first object!
    SingletonClass *anotherSingleton;
    anotherSingleton = anotherSingleton->getInstance();
    cout << anotherSingleton << endl;

    Sleep(5000);

    return 0;
}

Only one object created and this object reference is returned each and every time afterwords.

SingletonClass instance created!
00915CB8
00915CB8

Here 00915CB8 is the memory location of singleton Object, same for the duration of the program but (normally!) different each time the program is run.

N.B. This is not a thread safe one.You have to ensure thread safety.


H
HugoTeixeira

The solution in the accepted answer has a significant drawback - the destructor for the singleton is called after the control leaves the main() function. There may be problems really, when some dependent objects are allocated inside main.

I met this problem, when trying to introduce a Singleton in the Qt application. I decided, that all my setup dialogs must be Singletons, and adopted the pattern above. Unfortunately, Qt's main class QApplication was allocated on stack in the main function, and Qt forbids creating/destroying dialogs when no application object is available.

That is why I prefer heap-allocated singletons. I provide an explicit init() and term() methods for all the singletons and call them inside main. Thus I have a full control over the order of singletons creation/destruction, and also I guarantee that singletons will be created, no matter whether someone called getInstance() or not.


If you are referring to the currently accepted answer you first statement is wrong. The destructor is not called until all static storage duration objects are destroyed.
R
Red.Wave

Has anyone mentioned std::call_once and std::once_flag? Most other approaches - including double checked locking - are broken.

One major problem in singleton pattern implementation is safe initialization. The only safe way is to guard the initialization sequence with synchronizing barriers. But those barriers themselves need to be safely initiated. std::once_flag is the mechanism to get guaranteed safe initialization.


N
Nicolas Holthaus

If you want to allocate the object in heap, why don't use a unique pointer. Memory will also be deallocated since we are using a unique pointer.

class S
{
    public:
        static S& getInstance()
        {
            if( m_s.get() == 0 )
            {
              m_s.reset( new S() );
            }
            return *m_s;
        }

    private:
        static std::unique_ptr<S> m_s;

        S();
        S(S const&);            // Don't Implement
        void operator=(S const&); // Don't implement
};

std::unique_ptr<S> S::m_s(0);

Deprecated in c++11. unique_ptr is recommended instead. cplusplus.com/reference/memory/auto_ptr cplusplus.com/reference/memory/unique_ptr
This isn't thread safe. Better to make m_s a local static of getInstance()and initialize it immediately without a test.
Comparing m_s.get() with nullptr would be better than with 0.
M
Milind Deore

C++11 Thread safe implementation:

 #include <iostream>
 #include <thread>


 class Singleton
 {
     private:
         static Singleton * _instance;
         static std::mutex mutex_;

     protected:
         Singleton(const std::string value): value_(value)
         {
         }
         ~Singleton() {}
         std::string value_;

     public:
         /**
          * Singletons should not be cloneable.
          */
         Singleton(Singleton &other) = delete;
         /**
          * Singletons should not be assignable.
          */
         void operator=(const Singleton &) = delete;

         //static Singleton *GetInstance(const std::string& value);
         static Singleton *GetInstance(const std::string& value)
         {
             if (_instance == nullptr)
             {
                 std::lock_guard<std::mutex> lock(mutex_);
                 if (_instance == nullptr)
                 {
                     _instance = new Singleton(value);
                 }
             }
             return _instance;
         }

         std::string value() const{
             return value_;
         }
 };

 /**
  * Static methods should be defined outside the class.
  */
 Singleton* Singleton::_instance = nullptr;
 std::mutex Singleton::mutex_;


 void ThreadFoo(){
     std::this_thread::sleep_for(std::chrono::milliseconds(10));
     Singleton* singleton = Singleton::GetInstance("FOO");
     std::cout << singleton->value() << "\n";
 }

 void ThreadBar(){
     std::this_thread::sleep_for(std::chrono::milliseconds(1000));
     Singleton* singleton = Singleton::GetInstance("BAR");
     std::cout << singleton->value() << "\n";
 }

 int main()
 {
     std::cout <<"If you see the same value, then singleton was reused (yay!\n" <<
                 "If you see different values, then 2 singletons were created (booo!!)\n\n" <<
                 "RESULT:\n";
     std::thread t1(ThreadFoo);
     std::thread t2(ThreadBar);
     t1.join();
     t2.join();
     std::cout << "Complete!" << std::endl;

     return 0;
 }

A simple local static function variable is thread safe if your C++ compiler is standards compliant. No need for all the mutex magic. It does mean that static initializers can cause deadlock so one needs to be careful, but so does your suggested code here.
T
T.E.D.

It is indeed probably allocated from the heap, but without the sources there is no way of knowing.

The typical implementation (taken from some code I have in emacs already) would be:

Singleton * Singleton::getInstance() {
    if (!instance) {
        instance = new Singleton();
    };
    return instance;
};

...and rely on the program going out of scope to clean up afterwards.

If you work on a platform where cleanup must be done manually, I'd probably add a manual cleanup routine.

Another issue with doing it this way is that it isn't thread-safe. In a multithreaded environment, two threads could get through the "if" before either has a chance to allocate the new instance (so both would). This still isn't too big of a deal if you are relying on program termination to clean up anyway.


you can deduce, since you can see that instance variable is a pointer to the class instance.
There is no need to dynamically allocate the singleton. In fact this is a bad idea as there is not way to automatically de-allocate using the above design. Let it fall out of scope is does not call destructors and is just lazy.
You can automatically deallocate using the atexit function. That's what we do (not saying it's a good idea)
d
dan-man

In addition to the other discussion here, it may be worth noting that you can have global-ness, without limiting usage to one instance. For example, consider the case of reference counting something...

struct Store{
   std::array<Something, 1024> data;
   size_t get(size_t idx){ /* ... */ }
   void incr_ref(size_t idx){ /* ... */}
   void decr_ref(size_t idx){ /* ... */}
};

template<Store* store_p>
struct ItemRef{
   size_t idx;
   auto get(){ return store_p->get(idx); };
   ItemRef() { store_p->incr_ref(idx); };
   ~ItemRef() { store_p->decr_ref(idx); };
};

Store store1_g;
Store store2_g; // we don't restrict the number of global Store instances

Now somewhere inside a function (such as main) you can do:

auto ref1_a = ItemRef<&store1_g>(101);
auto ref2_a = ItemRef<&store2_g>(201); 

The refs don't need to store a pointer back to their respective Store because that information is supplied at compile-time. You also don't have to worry about the Store's lifetime because the compiler requires that it is global. If there is indeed only one instance of Store then there's no overhead in this approach; with more than one instance it's up to the compiler to be clever about code generation. If necessary, the ItemRef class can even be made a friend of Store (you can have templated friends!).

If Store itself is a templated class then things get messier, but it is still possible to use this method, perhaps by implementing a helper class with the following signature:

template <typename Store_t, Store_t* store_p>
struct StoreWrapper{ /* stuff to access store_p, e.g. methods returning 
                       instances of ItemRef<Store_t, store_p>. */ };

The user can now create a StoreWrapper type (and global instance) for each global Store instance, and always access the stores via their wrapper instance (thus forgetting about the gory details of the template parameters needed for using Store).


r
ricab

Here is a mockable singleton using CRTP. It relies on a little helper to enforce a single object at any one time (at most). To enforce a single object over program execution, remove the reset (which we find useful for tests).

A ConcreteSinleton can be implemented like this:

class ConcreteSingleton : public Singleton<ConcreteSingleton>
{
public:
  ConcreteSingleton(const Singleton<ConcreteSingleton>::PrivatePass&)
      : Singleton<StandardPaths>::Singleton{pass}
  {}
  
  // ... concrete interface
  int f() const {return 42;}

};

And then used with

ConcreteSingleton::instance().f();

b
baris.aydinoz

This is about object life-time management. Suppose you have more than singletons in your software. And they depend on Logger singleton. During application destruction, suppose another singleton object uses Logger to log its destruction steps. You have to guarantee that Logger should be cleaned up last. Therefore, please also check out this paper: http://www.cs.wustl.edu/~schmidt/PDF/ObjMan.pdf


K
Kevin Marshall

My implementation is similar to Galik's. The difference is my implementation allows the shared pointers to clean up allocated memory, as opposed to holding onto the memory until the application is exited and the static pointers are cleaned up.

#pragma once

#include <memory>

template<typename T>
class Singleton
{
private:
  static std::weak_ptr<T> _singleton;
public:
  static std::shared_ptr<T> singleton()
  {
    std::shared_ptr<T> singleton = _singleton.lock();
    if (!singleton) 
    {
      singleton.reset(new T());
      _singleton = singleton;
    }

    return singleton;
  }
};

template<typename T>
std::weak_ptr<T> Singleton<T>::_singleton;

A
Ali Sajjad

Your code is correct, except that you didn't declare the instance pointer outside the class. The inside class declarations of static variables are not considered declarations in C++, however this is allowed in other languages like C# or Java etc.

class Singleton
{
   public:
       static Singleton* getInstance( );
   private:
       Singleton( );
       static Singleton* instance;
};
Singleton* Singleton::instance; //we need to declare outside because static variables are global

You must know that Singleton instance doesn't need to be manually deleted by us. We need a single object of it throughout the whole program, so at the end of program execution, it will be automatically deallocated.


u
uuu777

Here is my view on how to do proper singletons (and other non-trivial static objects): https://github.com/alex4747-pub/proper_singleton

Summary:

Use static initialization list to instantiate singletons at the right time: after entering main and before enabling multi-threading Add minor improvements to make it unit-test friendly.


A
Andrushenko Alexander

I would like to show here another example of a singleton in C++. It makes sense to use template programming. Besides, it makes sense to derive your singleton class from a not copyable and not movabe classes. Here how it looks like in the code:

#include<iostream>
#include<string>

class DoNotCopy
{
protected:
    DoNotCopy(void) = default;
    DoNotCopy(const DoNotCopy&) = delete;
    DoNotCopy& operator=(const DoNotCopy&) = delete;
};

class DoNotMove
{
protected:
    DoNotMove(void) = default;
    DoNotMove(DoNotMove&&) = delete;
    DoNotMove& operator=(DoNotMove&&) = delete;
};

class DoNotCopyMove : public DoNotCopy,
    public DoNotMove
{
protected:
    DoNotCopyMove(void) = default;
};

template<class T>
class Singleton : public DoNotCopyMove
{
public:
    static T& Instance(void)
    {
        static T instance;
        return instance;
    }

protected:
    Singleton(void) = default;
};

class Logger final: public Singleton<Logger>
{
public:
    void log(const std::string& str) { std::cout << str << std::endl; }
};



int main()
{
    Logger::Instance().log("xx");
}

The splitting into NotCopyable and NotMovable clases allows you to define your singleton more specific (sometimes you want to move your single instance).


S
Sarath Govind

It restrict instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system

class Singleton {
private:
    int data;
    static Singleton* instance;
    Singleton();
public:
    static Singleton* getInstance();
};
Singleton* Singleton::instance = 0;
Singleton::Singleton()
{
    this->data = 0;
    cout << "constructor called.." << endl;
}

 

Singleton* Singleton::getInstance() {
    if (!instance) {
        instance = new Singleton();
        return instance;
    }
}
int main() {
    Singleton *s = s->getInstance();
    Singleton *s1 =s1->getInstance();
    }

This has two issues. (1) getInstance() isn't thread safe: if multiple threads call getInstance() at the same time then multiple Singleton instances could be constructed meaning you have a memory leak. (2) If instance already exists, getInstance() has no return value, so you have undefined behaviour.
s
sdfsdaf

The paper that was linked to above describes the shortcoming of double checked locking is that the compiler may allocate the memory for the object and set a pointer to the address of the allocated memory, before the object's constructor has been called. It is quite easy in c++ however to use allocaters to allocate the memory manually, and then use a construct call to initialize the memory. Using this appraoch, the double-checked locking works just fine.


Unfortunately not. This has been discussed in great depth by some of the best C++ developers out there. Double checked locking is broken in C++03.
A
Ali Khazaee

Simple singleton class, This must be your header class file

#ifndef SC_SINGLETON_CLASS_H
#define SC_SINGLETON_CLASS_H

class SingletonClass
{
    public:
        static SingletonClass* Instance()
        {
           static SingletonClass* instance = new SingletonClass();
           return instance;
        }

        void Relocate(int X, int Y, int Z);

    private:
        SingletonClass();
        ~SingletonClass();
};

#define sSingletonClass SingletonClass::Instance()

#endif

Access your singleton like this:

sSingletonClass->Relocate(1, 2, 5);

G
Gank
#define INS(c) private:void operator=(c const&){};public:static c& I(){static c _instance;return _instance;}

Example:

   class CCtrl
    {
    private:
        CCtrl(void);
        virtual ~CCtrl(void);

    public:
        INS(CCtrl);