Const is a promise that the variable declared as const, will not change. It’s a promise, hence it can be broken.

When we deal with const and pointers, it can be used in 2 ways.

  1. making the value constant
  2. making the memory address that it points to constant.
const int a = 2;
a = 5; //throws error. Can’t change it.
//How to read const? : Read it from right to left.
const int *b; //pointer to an int constant
int const *b; //pointer to a constant integer
//above 2 statements mean the same thing.
int * const b;//constant pointer to an integer
const int* const a; //constant pointer to an integer constant

Constant functions: Always make your methods const, if they do not modify members.

void GetA () const { return a; } 
//makes sure that the method doesn't modify a. Good for getters.

What if we need to modify some variable, but keep all others constant. How do we make sure?

class TestClass
{
  int m_a, m_b;
  mutable int m_c; //can be changed by constant functions too!
  void GetA() const { m_c++; return m_a; } 
  //modifies m_c but can't modify m_a
}

Hope you learnt something new today.