Can I initialize a static const member at run-time in C++?

Question

Is it possible to initialize a static const member of my class during run-time? This variable is a constant throughout my program but I want to send it as a command-line arg

Answer 1

Method #1: Initialize a hidden non-const variable, and provide a const reference to it (as shown by dasblinkenlight):

class A {
public: 
  static const int &T;
};

static int dummy = 0;
const int &A::T  = dummy;

int main() {
  dummy = 10;
  std::cout << A::T << std::endl;
}

Live Demo

Method #2: Use a non const static member (as shown by R Sahu):

class A {
public: 
  static int T;
};

int A::T = 0;

int main() {
  A::T = 10;
}

Live Demo

Method #3: Declare a hidden non-const variable as a private static member of your class and provide a static member const reference to interface it. Define a friend function as inititalizer:

class A {
  friend void foo(int);
    static int dummy;
public: 
    static const int &T;
};

const int &A::T = A::dummy;
int A::dummy = 0;

void foo(int val) { A::dummy = val; }

int main() {
    foo(10);
    std::cout << A::T << std::endl;
}

Live Demo

Method #4: Declare a hidden non-const variable as a private static member of your class and provide a static member const reference to interface it. Define a static member function as inititalizer:

class A {
    static int dummy;
public: 
    static const int &T;
    static void foo(int val) { A::dummy = val; }
};

const int &A::T = A::dummy;
int A::dummy = 0;

int main() {
    A::foo(10);
    std::cout << A::T << std::endl;
}

Live Demo

Bonus:

If you want to initialize only once you can change the helper function to:

static void foo(int val) { 
  static bool init = true;
  if(init) A::dummy = val;
  init = false;
}

Live Demo