static.cpp

#include <iostream>

class Test {
public:
  Test() {
    instance_count++;
  }

  static void printCounter() { std::cout << instance_count  << std::endl; }
private:
  static int instance_count;
};

class SubTest : public Test {};

int Test::instance_count = 0;

int main(int argc, char **argv) {
  Test();
  Test();
  SubTest();

  /* Will print 3 twice */
  Test::printCounter();
  SubTest::printCounter();

  return 0;
}