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C++ creation of objects

Posted on 2000-04-23
Last Modified: 2010-04-02
How I can create only one object of a class ?It should be only one object for it.
Question by:ankit_p_a

Expert Comment

ID: 2742989
Hi Ankit
Can you be more precise?


Author Comment

ID: 2742995
I have a class myclass with one data member.Now I want to create only one object of myclass.I must not be allowed to create more than one object.If I try to do so it should give message i.e
error,by saying it is not possible

Accepted Solution

kishore_joshi earned 75 total points
ID: 2743000
Hai ,
Here class A is called as a Singleton class. The ristriction is placed that ONLY ONE object of that class can be created.

class A
static int count;



static A* CreateObj()
     A *a = new A;
    if(count > 1)
      cout<<" Crossed the limit........ ";
      return NULL;

      return a;



int A::count;

void main()

      A *r1,*r2 ,*r3;

      r1 = A::CreateObj();
      r2 = A::CreateObj();
      r3 = A::CreateObj();

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Expert Comment

ID: 2743183
kishore_joshi ,you put the constructor in private ,how can ?

Expert Comment

ID: 2743236

Only if u put the constructor in the private, u can force the user to create the object by calling that static function CreateObj. Here in this function, we can check the value of static variable "count" and thus keep a control on the number of objects getting created.


Expert Comment

ID: 2743813
kishore_joshi ,if you define constructor explicitly in private part.Aint this compiler error ?
The compiler cannot call constructor when we use new to create objects...

Expert Comment

ID: 2746116
Hi Eirnava,
Its NOT compiler error. By declaring constructor in the private, we are forcing
the user to create the object only thru a static function.

If u declare the Copy Costructor (CC) also in the private, then u place another restriction on the user .....
i.e. u cannot pass the object of that class by value to any function, u HAVE to pass the object ONLY by reference.

Please try and execute the example that I have mentioned in the answer.
It should be more clear.  


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