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Pointer to Pointer Issue


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#1 DishSoap   Members   -  Reputation: 413

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Posted 26 February 2014 - 10:59 AM

*EDIT* As Ardvajk pointed out, while printing I am using the variable 'used' which == elements in the map. I should be using the number of bins or buckets in my array. 

 

Hey everyone, I'm having some strange issues I was hoping someone could help with. Basically I am inserting into a HashSet at the same index in an array [0] in my case. And when I loop through to print all the elements in the set I get some strange output for the bucket at index [1] even though I believe it to be completely empty. Also, this is a homework assignment, so just some guidance and not an outright answer would be appreciated smile.png

 

I am building a HashSet where the map is basically a pointer to a pointer of nodes. Hopefully I'm not posing a wall of code here next, as that would be annoying. But I have to post quite a bit for you to see what's going on. The declaration looks as such:

Node** set      = nullptr;
...
Node (T v,  Node* n = nullptr) : value(v), next(n){} // Relevant constructor

In my constructor for the HashSet I initialize the set to such:

template<class T>
HashSet<T>::HashSet(int (*func)(const T& element), double load) : hash(func), load_factor(load) {
	set = new LN*[bins];
	for(int i = 0; i < bins; i++) set[i] = nullptr;
}

My insert statement looks like this:

template<class T>
int HashSet<T>::insert(const T& element) {
  //write code here
	if(!contains(element))
	{
		int index = hash_compress(element);
	        Node* temp = set[index];
		if(temp == nullptr)
		{
			temp = new LN(element);
			set[index] = temp;
		}
		else
		{
			Node* new_node = new LN(element, set[index]);
			set[index] = new_node;
		}
		maintain_load(++used);
	}
}

Ok, that's all I will post. As I don't want to post too much, but I am happy to give more code if needed. Basically in my test, you will have to trust that int index = 0 for two inserts. After the second insert, the item gets properly inserted into bucket 0 but basically fills bucket 1 with a ton of garbage. To be exact, when I go to print it out all of my environment variables and the alphabet print out, it's kind of funny looking smile.png

 

My print method basically looks like this:

for(int i = 0; i < bins; i++) // used to be i < used
	{
		Node* temp = set[i];
		std::cout << "[" << i << "]" << std::endl;
		std::cout << "{" << std::endl;
		while(temp != nullptr)
		{
			std::cout << temp->value << std::endl;
			temp = temp->next;
		}
		std::cout << "}" << std::endl;
	}

Edited by DishSoap, 26 February 2014 - 02:26 PM.


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#2 DishSoap   Members   -  Reputation: 413

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Posted 26 February 2014 - 11:39 AM

Haha. I figured it out driving to school. Funny how a 10 minute break after staring at something for hourd makes you realize your mistaked. How can I delete this thread??

#3 Aardvajk   Crossbones+   -  Reputation: 6255

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Posted 26 February 2014 - 11:45 AM

You seen to be incrementinf your used variable upon any insert, the when printing, using it as a count of the hash entries. Two inserts with a hash of 0 will leave hash bucket 1 empty, but your print code thinks 0 and 1 are used hashes.

Hard to be sure viewing this on mobile but seems odd to me.

#4 Aardvajk   Crossbones+   -  Reputation: 6255

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Posted 26 February 2014 - 11:46 AM

Haha. I figured it out driving to school. Funny how a 10 minute break after staring at something for hourd makes you realize your mistaked. How can I delete this thread??


Don't delete, post your fix. Might be useful to someone in the future searching for a similar issue.

#5 DishSoap   Members   -  Reputation: 413

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Posted 26 February 2014 - 12:01 PM

That was exactly the issue. I will fix my post when I get home.

 

*EDIT*

Home now! I fixed it. Thank you.


Edited by DishSoap, 26 February 2014 - 02:27 PM.





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