A variable that is read-only after assignment at run-time?

Question

Fairly new programmer here, and an advance apology for silly questions.

I have an int variable in a program that I use to determine what the lengths of my arrays should be in some of my structures. I used to put it in my header as a const int. Now, I want to fork my program to give the variable different values depending on the arguments given in, but keep it read-only after I assign it at run-time.

A few ideas I've had to do this. Is there a preferred way?

1. Declare a const int * in my header and assigning it to a const int in my main function, but that seems clunky.
2. Make it a plain int in my main function.
3. Pass the variable as an argument when the function is called.
4. Something else I haven't thought of yet.

Answer 1

I'd use a function-static variable and a simple function. Observe:

int GetConstValue(int initialValue = 0)
{
  static int theValue = initialValue;
  return theValue;
}

Since this is a function-level static variable, it is initialized only the first time through. So the initialValue parameter is useless after the first run of the function. Therefore, all you need to do is ensure that the first call of the function is the one that initializes it.