Static Functions

Static data types can be accessed without instantiation of the class in C++. This is applicable for static functions also.

The differences between a static member function and non-static member functions are as follows.

• A static member function can access only static member data, static member functions and data and functions outside the class. A non-static member function can access all of the above including the static data member.
  
• A static member function can be called, even when a class is not instantiated, a non-static member function can be called only after instantiating the class as an object.
  
• A static member function cannot be declared virtual, whereas a non-static member functions can be declared as virtual
  
• A static member function cannot have access to the 'this' pointer of the class.

The static member functions are not used very frequently in programs. But nevertheless, they become useful whenever we need to have functions which are accessible even when the class is not instantiated.

Copy constructor

Copy constructor is

• a constructor function with the same name as the class
• used to make deep copy of objects.

There are 3 important places where a copy constructor is called.

1. When an object is created from another object of the same type
2. When an object is passed by value as a parameter to a function
3. When an object is returned from a function

If a copy constructor is not defined in a class, the compiler itself defines one. This will ensure a shallow copy. If the class does not have pointer variables with dynamically allocated memory, then one need not worry about defining a copy constructor. It can be left to the compiler's discretion.

But if the class has pointer variables and has some dynamic memory allocations, then it is a must to have a copy constructor.

---

For ex:
class A //Without copy constructor
{
private:
int x;
public:
A() {A = 10;}
~A() {}
}

---

class B //With copy constructor
{
private:
char *name;
public:
B()
{
name = new char[20];
}
~B()
{
delete name[];
}
//Copy constructor
B(const B &b)
{
name = new char[20];
strcpy(name, b.name);
}
};

---

Let us Imagine if you don't have a copy constructor for the class B. At the first place, if an object is created from some existing object, we cannot be sure that the memory is allocated. Also, if the memory is deleted in destructor, the delete operator might be called twice for the same memory location.

This is a major risk. One happy thing is, if the class is not so complex this will come to the fore during development itself. But if the class is very complicated, then these kind of errors will be difficult to track.

In Windows this will lead to an application popup and unix will issue a core dump. A careful handling of this will avoid a lot of nuisance