How to initialize static std::array with static const variable?

Question

How to initialize static std:array that uses static const variable as size? I tried searching for similar questions but std::array is relatively new so theres not much to be found.

// ExampleClass.h
class ExampleClass {
 public:
 static const size_t NUMBER_OF_INDEXES = 5;
 private:
 static std::array<int, NUMBER_OF_INDEXES> myArray;
};

Answer 1

Like any other static data member, ExampleClass::myArray should have an out-of-line definition in exactly one translation unit, where you write down its type and its qualified name as usual:

std::array<int, ExampleClass::NUMBER_OF_INDEXES> ExampleClass::myArray = {1, 2, 3, 4, 5};

Answer 2

Works fine with newer standards/compilers. I tried your code and it runs fine when using C++20 or C++23:

#include <array>
#include <stdint.h>
#include <iostream>
class ExampleClass {
 public:
 static const std::size_t NUMBER_OF_INDEXES = 5;
 private:
 static std::array<int, NUMBER_OF_INDEXES> myArray;
 public:
 void printSize(){
 std::cout << myArray.size() << std::endl;
 }
 
};
int main()
{
 ExampleClass obj;
 obj.printSize();
 return 0;
}

https://onlinegdb.com/lVycEuQmE

P.S. For those who opened the question wondering if they can convert C-style array to std::array - yes, you can using C++20 std::to_array()