Defining Static Data Member

Access Static Members Without Any Object

To access the static data member of any class we have to define it first.

Below is the C++ program to show how to resolve the above error:

C++

// C++ program to access static data
// member with explicit definition
#include <iostream>
using namespace std;
 
class A {
    int x;
 
public:
    A() 
    { 
      cout << "A's constructor called " << 
               endl; 
    }
};
 
class B {
    static A a;
 
public:
    B() 
    { 
      cout << "B's constructor called " << 
               endl; 
    }
    static A getA() 
    { 
      return a; 
    }
};
 
// Definition of a
A B::a; 
 
// Driver code
int main()
{
  B b1, b2, b3;
  A a = b1.getA();
 
  return 0;
}

Output

A's constructor called 
B's constructor called 
B's constructor called 
B's constructor called

Explanation: The above program calls B’s constructor 3 times for 3 objects (b1, b2, and b3), but calls A’s constructor only once. The reason is that the static members are shared among all objects. That is why they are also known as class members or class fields.

Also, static members can be accessed without any object.

NOTE: Static data members can only be defined globally in C++. The only exception to this are static const data members of integral type which can be initialized in the class declaration.

C++ Static Data Members

Static data members are class members that are declared using static keywords. A static member has certain special characteristics which are as follows:

Only one copy of that member is created for the entire class and is shared by all the objects of that class, no matter how many objects are created.
It is initialized before any object of this class is created, even before the main starts.
It is visible only within the class, but its lifetime is the entire program.

Syntax:

static data_type data_member_name;

Below is the C++ program to demonstrate the working of static data members:

C++

// C++ Program to demonstrate 
// the working of static data member
#include <iostream>
using namespace std;
 
class A {
public:
    A() 
    { 
      cout << "A's Constructor Called " << 
               endl; 
    }
};
 
class B {
    static A a;
 
public:
    B() 
    { 
      cout << "B's Constructor Called " << 
               endl; 
    }
};
 
// Driver code
int main()
{
    B b;
    return 0;
}

Output

B's Constructor Called

Explanation: The above program calls only B’s constructor, it doesn’t call A’s constructor. The reason is,

Static members are only declared in a class declaration, not defined. They must be explicitly defined outside the class using the scope resolution operator.

Tags:

#Static Keyword #C++ #CPP

Accessing a Static Member

Access Static Members Without Any Object

Defining Static Data Member

C++

C++ Static Data Members

C++

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