Do Static Variables in Member Functions Share Values Across Class Instances?

Static Variables in Member Functions: Shared or Instance-Specific?

Static variables within member functions possess unique behavior in C . Consider the class definition below:

class A {
   void foo() {
      static int i;
      i++;
   }
};

The question arises: if multiple instances of class A are created, does invoking foo() on one instance modify the static variable i for all instances?

Contrary to the expectation of individual i copies for each instance, static variables in member functions behave differently. In the given example, only one copy of the static variable i exists within the entire program.

Any instance of class A affects the same i variable, which persists throughout the program's lifetime. To illustrate:

A o1, o2, o3;
o1.foo(); // i = 1
o2.foo(); // i = 2
o3.foo(); // i = 3
o1.foo(); // i = 4

Therefore, each call to foo() for any instance of class A increments the shared i variable. These static variables provide a mechanism for sharing data across all instances of a class.

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