C++ Static Members of Class(Variables shared)

Lesson 8	Static members of a class
Objective	Explore the use of static members in a class.

C++ Static Members of Class

Data members of a class can be declared with the storage class modifier static. A data member that is declared static is shared by all variables of that class and is stored in only one place. Nonstatic data members are created for each instance of the class. Since a static member is independent of an particular instance, it can be accessed in the form (see below). [*]

[*]
class name :: identifier

A static member of a global class must be explicitly declared and defined in file scope.
Let us look at an example:

class str {
public:
   static int  how_many;  //declaration
   void print();
   void  assign(const char*);
   .....
private:       //implement fixed length char array
   char  s[100];
};

int str::how_many = 0;    //definition and init

In our example, how_many could track how much memory is being used to store str variables. Therefore:

str   s1, s2, s3, *p;

str::how_many = 3;
   .....
str t;
t.how_many++;       //dot operator to access
   .....
p = new str;
p -> how_many++; //pointer operator to access
   .....
delete p;
str::how_many--;