What are static variables?

Static variables in programming have the following characteristics:

• Lifetime: They exist throughout the entire runtime of the program.
• Scope: Depends on where they are defined (can be local to a function or global within a file/class).
• Initialization: They are initialized once at program startup (or upon first access, depending on the language) and retain their value between function or class method calls.
• Memory: Usually stored in the data segment of statically allocated memory.

Examples of usage:

• Counting the number of function calls.
• Storing a state shared among all instances of a class (in case of static class members).
• Implementing the Singleton pattern.

Example in C++:

#include <iostream>

void counter() {
    static int count = 0; // Static local variable
    count++;
    std::cout << "Function called " << count << " times" << std::endl;
}

int main() {
    counter(); // Output: Function called 1 times
    counter(); // Output: Function called 2 times
    counter(); // Output: Function called 3 times
    return 0;
}

Example of a static class member in Python:

class MyClass:
    class_variable = 0  # Static class variable

    def __init__(self):
        MyClass.class_variable += 1

    def display_count(self):
        print(f"Current count: {MyClass.class_variable}")

obj1 = MyClass()
obj2 = MyClass()

obj1.display_count() # Output: Current count: 2
obj2.display_count() # Output: Current count: 2