Ways to change const value in c++

Question

const value is often used in programming. It gives programmer security that the value will not change in future. Unfortunately, this is not fully enforced. As a consequence it sometimes causes subtle bugs that are very hard to decipher. As an example :

int a = 1;
const int& b = a; // I promise I will not change
a = 3; // I am a liar, I am now 3
cout << b; // As I will now show 3

It is possible to change const values in other ways also; some of them are quite complex and require good amount of code which often gets lost in other segment of code and hence causing bug.

Thus would anyone elaborate upon the possible ways to change a const value? Don't worry if you don't know all, many wouldn't (including myself). Just tell all of the ways you know - after all you can only give what you have!

Answer 1

const int& b = a; // I only promise I will not change the value via b, nothing more.

const doesn't guarantee the value won't be changed by other references or pointers. Think of the following code:

void f(const int& b) { ... }
...
int a = ...;
f(a);
a = ...;

The value of a won't be changed inside f() (by the passed argument), that's all the guarantee.

const is just a helper. If you won't change sth, then make it const, then compiler will help you to check it. You still could change the original value in other ways like your code showed, it's still your responsibility, finally.