(C++) static

Keyword enabling in-class or in-function static variables or create static member function.

A common use of static is when you want to keep track of how many instances a class has:

#include <iostream>

class instance_counter
{
  static int m_n_instances;
  
  public:
  instance_counter()
  {
    ++m_n_instances;
    std::cout << "Constructed an instance."
      << "Now there are " << m_n_instances << ".\n";
  }
  ~instance_counter()
  {
    --m_n_instances;
    std::cout << "Destructed an instance."
      << "Now there are " << m_n_instances << ".\n";
  }
};

int instance_counter::m_n_instances = 0;

int main()
{
  instance_counter one, two, three, four,five;
}

Advice

• See static member function

Notes to self

• When in doubt if a variable should be static or not, do not make it static: I note that I do change variables from static to non-static, but never the other way around

External links

• CppCon 2017: Nir Friedman 'What C++ developers should know about globals (and the linker)'