Interview question: Can you implement an object counter program in C++ for a class that count the number of objects created for that class.
Answer: Actually, counting object in C++ implementation is simple.
Solution is, to create a static variable, say “objCount” and a static method like “GetObjectCount()” that returns number of objects created for the class.
[Why static variable & static method in C++? – Since, a static variable is shared by all the instances of the class, all the objects will increment the persisting value of “objCount”. And a static method, so, we can call by class name not by using any instance of the class.]
Secondly, we have to increment objCount in class constructor and copy constructor and decrement it into class destructor.
Example:
#include
using namespace std;
class A{
static int objCount; // counter to count the object
public:
A()
{
++objCount;
}
A(const A &a)
{
++objCount;
}
~A()
{
--objCount;
}
/* Retruns the number of objects created for this class*/
static int GetObjectCount() {
return objCount;
}
//other methods
void MethodOne(){
cout<< "Method Two..."<<"\n";
}
void MethodTwo(){
cout<< "Method Two..."<<"\n";
}
};
int A::objCount = 0; // initialize static variable
int main(){
cout<< "\nTest object counter..."<<"\n";
A obj1; // statically created object
A obj2;
A *obj3 = new A(); //dynamically created object
A *obj4 = new A();
cout<< "\nNumber of objects alive so for : "<< A::GetObjectCount()<<"\n";
delete obj3;
delete obj4;
A obj5 = obj1; // invokes copy constructor
cout<< "\nNumber of objects alive so for : "<< A::GetObjectCount()<<"\n";
return 0;
}
Output:
Test object counter…
Number of objects alive so for : 4
Number of objects alive so for : 3