Static function members in C+

Static member functions (C++ only)
You cannot have static and nonstatic member functions with the same names and the same number and type of arguments.
Like static data members, you may access a static member function f() of a class A without using an object of class A.
A static member function does not have a this pointer.

Eg.
class X
{
private:
   static int si;
public:
   static void set_si(int arg) { si = arg; }
};


Static member functions (C++ only)

The compiler does not allow the member access operation this->si in function A::print_si() because this member function has been declared as static, and therefore does not have a this pointer.

You can call a static member function using the this pointer of a nonstatic member function. In the following example, the nonstatic member function printall() calls the static member function f() using the this pointer:

#include < iostream >

using namespace std;

class C {
  static void f() {
    cout << "Here is i: " << i << endl;
  }
  static int i;
  int j;
public:
  C(int firstj): j(firstj) { }
  void printall();
};

void C::printall() {
  cout << "Here is j: " << this->j << endl;
  this->f();
}

int C::i = 3;

int main() {
  C obj_C(0);
  obj_C.printall();
}

A static member function cannot be declared with the keywords virtual, const, volatile, or const volatile.
A static member function can access only the names of static members, enumerators, and nested types of the class in which it is declared. Suppose a static member function f() is a member of class X. The static member function f() cannot access the nonstatic members X or the nonstatic members of a base class of X.

Const data members in c++

Static data member in c++ classes

Note: Static data member are already initialised to 0, but still you should initialise explicitly using method 2.
Here are the two ways I was talking about :
First One:

class class1{

private:

public:


class1(){}


static int DataMember;


static void initFun()

{ DataMember = 10 ; }

};

Second One:

class class2{

private:

public:


class2(){}


static int DataMember2;


};

int class2::DataMember2 = 10 ;

Once you define a static data member, it exists even though no objects of the static data member's class exist. In the above example, no objects of class X exist even though the static data member X::i has been defined.

Static data members of a class in namespace scope have external linkage. The initializer for a static data member is in the scope of the class declaring the member.

A static data member can be of any type except for void or void qualified with const or volatile. You cannot declare a static data member as mutable.

You can only have one definition of a static member in a program. Unnamed classes, classes contained within unnamed classes, and local classes cannot have static data members.

Static data members and their initializers can access other static private and protected members of their class.