How to calculate hash value for pointers?

Question

I want to create a hash table where I can store value with pointers as key. For example In C++ if we define a linked list as:

struct Node{
 int val;
 Node* next;
}

I can create a hash table with pointers of Node using std::unordered_map or std::map like:

unordered_map<Node*,int> um;
Node* a = (Node*)malloc(sizeof(Node));
um[a]=12;
cout<<um[a]<<endl //This prints 12

Now if I want to do this without the standard library how can I calculate the hash value for Node pointers?

[What's the difference between “STL” and “C++ Standard Library”?](https://stackoverflow.com/questions/5205491/whats-the-difference-between-stl-and-c-standard-library) — François Andrieux, Mar 06 '20 at 16:14
If you are writing your hash implementation, you may find [Coding up a Hash Table](http://www.sparknotes.com/cs/searching/hashtables/section3.rhtml) and [Hash tables - eternally confuzzled](http://eternallyconfuzzled.com/tuts/datastructures/jsw_tut_hashtable.aspx) useful. — David C. Rankin, Mar 06 '20 at 16:15
@FrançoisAndrieux perhaps we just edit and use `"C++ containers"` instead of `"STL"`? (which is what I take it to mean...) — David C. Rankin, Mar 06 '20 at 16:24
Side note: In C++ `malloc` carries some risk. It does not call constructors so complicated objects are left as ticking time-bombs, ready to explode as soon as you try to use them improperly initialized. Users of the code will likely use `delete` to instead of `free` to release the allocation, and Crom only knows how that will turn out. — user4581301, Mar 06 '20 at 16:32

score 5 · Answer 1 · answered Mar 06 '20 at 16:11

5

Cast them to uintptr_t and then calculate the hash values for integers.

answered Mar 06 '20 at 16:11

user253751

One more bit of useful information: The above works because pointers should already be unique identifiers. If they aren't you have other problems. – user4581301 Mar 06 '20 at 16:28

1 Answers1