Assigning pointer to bitwise OR of two pointers

Question

I'm implementing remove method for binary search tree in C++. In one of cases I am sure that tree node has only one child: node->left or node->right and I need to modify it's parent to point to that child. As I mentioned before one of node->left and node->right are NULL. Here's a snippet:

} else { // One children
  if (node->parent->left == node) {
    node->parent->left = node->left | node->right;
    node->parent->left->parent = node->parent;
  } else {
    node->parent->right = node->left | node->right;
    node->parent->right->parent = node->parent;
  }
}

Unfortunatelly, compiler returns an error. I know that it's maybe not the elegant one but I was just curious how to do it.

@Walter Pointers are numbers. So if I OR two numbers from which one is zero (NULL) I should get the second number. — keepkimi, Oct 28 '13 at 20:22
@keepkimi First of all, pointers are not numbers. They are pointers. Second, `NULL` is not necessarily the number 0. — , Oct 28 '13 at 20:23
[null pointers aren't necessarily 0](http://stackoverflow.com/q/2759845/1281433) — Joshua Taylor, Oct 28 '13 at 20:24
Wow, harsh crowd. I don't see any reason why this needed to be put on hold. — Mark Ransom, Oct 28 '13 at 22:17
To be more specific: it's well known that pointers contain addresses, and addresses consist of a bit pattern. Asking why bit manipulation of an address doesn't work is perfectly valid. Someone coming from an assembler background would especially be confused, although I suspect that's rare these days. — Mark Ransom, Oct 28 '13 at 22:34

score 7 · Accepted Answer · answered Oct 28 '13 at 20:24

Bit manipulation on pointers isn't supported by C++ or C. You can convert them to integers, do the or, then convert back, but that's just asking for trouble for no particular gain.

Use ternary expressions instead:

node->parent->left = node->left ? node->left : node->right;

score 1 · Answer 2 · answered Oct 28 '13 at 20:25

I'm not sure that would achieve what you want. Assigning your pointers the result of a bitwise OR of two other pointers would result in a pointer that points to who knows where.

I think what you are looking for is something like this:

} else { // One children
  if (node->parent->left == node) {
    node->parent->left = node->left != null ? node->left : node->right;
    node->parent->left->parent = node->parent;
  } else {
    node->parent->right = node->left | node->right;
    node->parent->right->parent = node->parent;
  }
}

Assigning pointer to bitwise OR of two pointers

2 Answers2