Dynamic Array of Linked Lists

[gtateco]

Hi, I'm trying to do a hashing project using separate chaining. In order to do the separate chaining I believe I need to make a dynamic array of pointers to the linked lists. This is due to the fact the user can specify the hash table size at runtime. In VS2010 when I try to set the HEAD pointer values to NULL it won't compile and returns "no operator found which takes a right-hand operand of type 'int' (or there is no acceptable conversion)".

My code is super simple so I'm not sure what I am doing wrong. Any help would be great. Thx, Glenn.

struct list 
{
   list *next;
   list *prev;
   int numValue;
};

void separateChaining(int hashTable[], int hashTableSize)
{
	list * listArray;
	listArray = new list[hashTableSize];
	if(listArray == NULL)
	{
		cout << endl << "Memory error creating array of linked lists!";
		system("PAUSE");
		return;
	}
     for(int i = 0; i < hashTableSize; i++)
     {
             listArray[i] = NULL;
     }    

}

[daviddoria]

Can you use a std::vector<list>?

Also I would be very careful with the name "list". If somewhere else std::list gets included, then you're going to have conflicts.

Dave

[Agni]

You are not setting the pointer to NULL you are trying to assign an initialized object of type list to NULL and there is no such assignment operator.

[gtateco]

I can not use vector unfortunately. Thanks for the tip about list, I changed my code. I've totally changed strategy as I think my problems is trying to do everything with the one Struct. I've created another struct to hold the initial hash value and HEAD/TAIL pointers to the linked lists. See below.

struct hashType
{
	listType *head;
	listType *tail;
	int numValue;
};

 for(int i = 0; i < hashTableSize; i++)
     {
         listArray[i].numValue = 0;    
		 listArray[i].head = NULL;
		 listArray[i].tail = NULL;
     }

I think I'm on the right track now, but please let me know if I've gone astray.

[mrnutty]

I hope there is no naming conflict here , since there is a std::list. But this code:

listArray = new list[hashTableSize];

will THROW and exception, instead of setting listArray to null. So there is no
reason to check if listArray is null, because you won't get a chance to check it, unless you use nothrow.

EDIT, from your previous post, you need a good constructor :

struct hashType{
	listType *head;
	listType *tail;
	int numValue;
 //use a initializer list, to initialize head,tail,numValue using its default constructor.
 hashType() : head(), tail(), numValue(){} 
};