If you modify content that a member variable points to, is that const?

I found an interesting fact that, in a class's const function, you can modify a member varialbe's deference, or the function's parameters, for example:

Code:

class A{
  int* ptr;
  void foo(int x) const{
   ++*ptr;
   x++;
 } 
};

Isn't that misleading in C++'s const method's regulation.

If you want the pointed-to stuff to be const, do so.

yep nothing strange about that.

The const means you can't modify any of the classes member variables so modifying the parameter passed in isn't surprisingly. While:
void foo(const int x) constis what prevents the modification of a parameter

Since the dereference is just memory somewhere you aren't modifying the ptr ptr , but rather what the pointer is pointing to which sounds normal. So operations like

Code:

++ptr;

or

Code:

int *b; ptr = b;

are prevented by the const as you are actually modifying the member variable.

What is a bit interesting is that you can indirectly modify a member variable in a const function.

Code:

class A{
  int* ptr;
  int g;

  A(){g = 5; ptr = &g}

  void foo(int x) const{
   ++*ptr; <--- Modifies the member variable g despite being a const.
 } 
};