34 CONST in C++

1. const

I like to call const a "fake keyword" because it doesn't actually do much when generating code.
It's somewhat like the visibility of classes and structs—a mandatory rule for developers to keep the code clean.
Essentially, const is a promise you make that certain things are immutable and won't change. However, it's just a promise, and you can bypass or break it, just like in real life.

*a = 2 refers to the dereferencing mentioned earlier.

const int* a = new int;
// Equivalent to int const* a = new int;
*a = 2;                           // Error: const prevents you from modifying the content pointed to by a
a = (int*)&MAX_AGE;

int* const a = new int;
*a = 2;
a = (int*)&MAX_AGE;               // Error: You can change the content pointed to by a, but you cannot reassign the pointer itself to point to something else

const int* const a = new int;      // Neither the content pointed to by a nor the pointer itself can be changed
*a = 2;
a = (int*)&MAX_AGE;

Key point: Pay attention to whether const is on the left or right side of *.

2. Using const in Classes and Methods

class Entity
{
private:
    int m_X, m_Y;
public:
    int GetX() const { // Promises that this method will not modify the class; it's a read-only method
        m_X = 2;       // Cannot modify
        return m_X;
    }
};

int* m_X, m_Y means m_Y is still an int type. To make both pointers, you need to write int* m_X, *m_Y.

A const object cannot call non-const member functions because the latter might modify the object.

You can mark a variable as mutable int var, allowing it to be modified even within a const method.