Thread: const question

Originally Posted by C3Pnuts

I know you're not talking pointers in your example but just to make sure you realize this, const char *Foo() is not the same as char * const Foo().

The first is a normal pointer to a constant char string (pointer can be changed but not the string being pointed to).
The second is a constant pointer to a normal char string (string being pointed to can be changed but not the pointer).

A subtle difference.

And there is everyone's favorite mind twister:
const char* const Foo()
aka
char const* const Foo()



Just felt like being obnoxious.
Cheers

Were you just kidding or does it rea;lly do something???
*Brain system shutting down...*

1) You can declare a pointer to a const. That prevents you from changing the value at the address stored in the pointer:

Code:

int x = 10;
int const* ptr1 = &x;
cout<<*ptr1<<endl;

*ptr1 = 20; //error

However, you can assign another address to the pointer:

Code:

int y = 20;
ptr1 = &y;
cout<<*ptr1<<endl;

2) You can declare a const pointer. That means the address stored in the pointer can't be changed:

Code:

int a = 30;
int* const ptr2 = &a;
cout<<*ptr2<<endl;

int b = 40;
ptr2 = &b; //error

However, you can change the value at that address:

Code:

*ptr2 = 40;
cout<<*ptr2<<endl;

3) You can declare a const pointer to a const. Than means the value at the address stored in the pointer cannot be changed, and the pointer cannot be assigned a different address:

Code:

int s = 50;
const int* const ptr3 = &s;
cout<<*ptr3<<endl;
int t = 60;

*ptr3 = t;  //error
ptr3 = &t; //error

4) You can declare a const member function. That means the member function is not allowed to change the calling object:

Code:

#include <iostream>

using namespace std;

class Apple
{
private:
	int size;

public:
	Apple(int s)
	{
		size = s;
	}
	void change_size() const
	{
		size = 30;
	}
};

int main()
{
	Apple a(3);
	a.change_size(); //error

	return 0;
}

5) You can declare a const member function that returns a const pointer to a const:

const int* const someFunc() const

6) You can declare a const member function that returns a const pointer to a const, and has a parameter that is a const pointer to a const:

const int* const someFunc(const int* const ptr) const