CODEWITHSUNDEEP
c++classsingleton
Naruto
Naruto

Reputation: 9634

What is the mistake in this singleton object creation code

In this, i am trying to copy singleton object to another object. Though i have overridden = operator, its giving me some problem. Kindly help. 

 class singleTon
        {
        public:
            static singleTon*  InitInstance()
            {
                if(singleTonObjPtr== NULL)
                {
                singleTonObjPtr = new singleTon;
                }
                return singleTonObjPtr;
            }

            singleTon* getObject()
            {
                return singleTonObjPtr;
            }

            singleTon(const singleTon& singletonObj)
            {

            }

            void operator =(const singleTon& singletonObj)
            {
                  return;
            }

        private:
            singleTon()
            {
                i = 50;
                singleTonObjPtr = NULL;
            }

            ~singleTon()
            {
            }

            int i;
            static singleTon* singleTonObjPtr;

        };

        singleTon* singleTon::singleTonObjPtr = NULL;


        int _tmain(int argc, _TCHAR* argv[])
        {
          singleTon *singleTOnPtr =NULL;
          singleTOnPtr = singleTon::InitInstance();
          singleTon *singleTOnPtr2 = singleTOnPtr->getObject();

          singleTon obj3 = *singleTon::InitInstance();
    }

Upvotes: 0

Views: 152

Answers (2)

Mike Seymour
Mike Seymour

Reputation: 254431

It might help if you read (and post) the compiler error. I get:

test.cpp:37: error: ‘singleTon::~singleTon()’ is private
test.cpp:55: error: within this context

where line 37 is the declaration of the private destructor, and line 55 is the point in _tmain at which the code tries to create and destroy an object, requiring a public destructor.

If you want to be able to create and destroy multiple copies of your confusingly-named-not-quite-singleton-thingy, then you'll need to make the destructor public. For this simple example, you can do that by removing the destructor altogether; the implicit constructor will be public, and there are no members that need non-trivial destruction.

Upvotes: 1

juanchopanza
juanchopanza

Reputation: 227370

First of all, operator= is the assignment operator, so you are assigning, not copying. Your assignment operator returns void, but it should return a singleTon&. But you really have to ask what the meaning of assigning to a singleton is. For example:

singleTon a = singleTon::InitInstance(); // single instance
singleTon b = singleTon::InitInstance(); // same instance
a = b; // assignment, but a and b really are the same instance, so what's the point?

And, for a singleton, there should no default-construction:

singleTon b; // this should not be allowed
b = a; // so this makes no sense

Upvotes: 2

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