Is it allowed to cast away const on a const-defined object as long as it is not actually modified?

Question

Is the following allowed:

const int const_array[] = { 42 };

int maybe_inc(bool write, int* array) {
  if (write) array[0]++;
  return array[0];
}

int main(         


        

Answer 1

If it compiles, then it is allowed. But it does not mean, it is legal.

#include 

int main(int argc, char *argv[]) 
{
    const int arr[] = {1, 2, 3};
    int* parr = const_cast(arr);
    parr[0] = 0;
    for(auto& n : arr)
        std::cout << n << std::endl;
}

The above code compiles in Ubuntu 20.04 g++ compiler. It also runs without problem. But the above code actually is undefined behaviour.