Const node iterator.
This is an
| Type | Definition | Description | 
| iterator_category | trivial_iterator_tag | Category. comment = | 
| difference_type | void | Difference type. | 
Note that a node iterator's value type is actually a tree iterator.
| Type | Definition | Description | 
| value_type | const_iterator | Iterator's value type. | 
| pointer | const_iterator * | Iterator's pointer type. | 
| const_pointer | const_iterator * | Iterator's const pointer type. | 
| reference | const_iterator & | Iterator's reference type. | 
| const_reference | const iterator & | Iterator's const reference type. | 
| Method | Description | Complexity Guarantee | Exception Guarantee | 
| inline const_node_iterator (const node_pointer p_nd = NULL) | Default constructor. | O(1) worst. | 3 | 
| Method | Description | Complexity Guarantee | Exception Guarantee | 
| inline const_iterator operator* () const | Access. | O(1) worst. | 3 | 
| Method | Description | Complexity Guarantee | Exception Guarantee | 
| inline const_node_iterator l_child () const | Returns the const node iterator associated with the left node. | O(1) worst. | 3 | 
| inline const_node_iterator r_child () const | Returns the const node iterator associated with the right node. | O(1) worst. | 3 | 
| Method | Description | Complexity Guarantee | Exception Guarantee | 
| inline bool operator== (const const_node_iterator &r_other) const | Compares content to a different iterator object. | O(1) worst. | 3 | 
| inline bool operator!= (const const_node_iterator &r_other) const | Compares content (negatively) to a different iterator object. | O(1) worst. | 3 |