Checking pointers

When you check to see that a pointer points to an existing object by using:

Code:

---

if (pointer)
  ...

---

how exactly does the program check the pointer's validity?

That is the lazy way of checking to make sure the pointer is not pointing to NULL.
NULL has a defined value of 0. But this only works if you make sure to set your pointers to NULL when you create them.

Code:

---

int * ptr = NULL;
ptr = new int[100];
if( ptr == NULL)
{
  cout << "Calling new failed, out of memory";
  return;
}
// ptr is valid now.
//do stuff
delete [] ptr;
//free the mem used

---

Well, syntax aside, when you call something like if (ptr == NULL), how does the program know if ptr points to valid memory or not since a pointer will always point to some portion of memory?

Quote:

---

Well, syntax aside, when you call something like if (ptr == NULL), how does the program know if ptr points to valid memory or not since a pointer will always point to some portion of memory?

---

The pointer does point to a memory address, but C++ allows it to also point to 0 or NULL often to signify a problem or for initialisation purposes.

If the pointer is NULL or 0 then the (ptr == NULL), expression will be (true). Its just a means to an end.