array reallocation C++

Question

Suppose you have an array, items, with capacity 5 and suppose also you have a count varaible that counts each entry added to the array. How would you realloacte the array? Using C++ syntax?

void BST::reallocate()
{
    item *new_array = new item[size*2]; 
 for ( int array_index = 0; array_index < size * 2; array_index++ ) 
    {
        if ( ! items[array_index].empty )
        {
   new_array[array_index].theData = items[array_index].theData;
   new_array[array_index].empty = false;
  }
    }
    maxSize += size;
    delete [] items;

    items = NULL;
    items = new_array;
 }

How do you reallocate an array? BST ctor is below with the private items struct, just to eliminate any confusion.

BST::BST(int capacity) : items(new item[capacity]), Position(0), 
leftChild(0), rightChild(0), maxSize(capacity)
{

}

this is in the BST header:

private:
 int size;
 int maxSize;
 int Position;
 int leftChild;
 int rightChild;
 struct item
 {
  bool empty;
  data    theData;

 };

 item *items;

The quesetion is that i seem to be having a hard time with the reallocation of my items array.

its crashing on assignment from items[i].theData to new_array[i].theData. — user40120
– user40120, Commented Nov 19, 2009 at 20:07
Aside: items = NULL is unnecessary, since you reassign items immediately afterwords. — outis
– outis, Commented Nov 19, 2009 at 20:30

David Thornley · Accepted Answer · 2009-11-19 20:07:27Z

8

I would reallocate it in the form of a std::vector<item>, assuming that there is no overriding reason to use an array. That would avoid several problems completely.

answered Nov 19, 2009 at 20:07

David Thornley

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Comments

Jerry Coffin · Accepted Answer · 2009-11-19 20:07:47Z

5

Why are you doing this at all? Why do you think that:

std::vector<item> items;

won't work for you?

answered Nov 19, 2009 at 20:07

Jerry Coffin

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Comments

JaakkoK · Accepted Answer · 2009-11-19 20:04:49Z

3

Your old array items has only size elements, so you need to change the upper limit in your for loop to size from size*2 when you're copying the old elements to the new array.

answered Nov 19, 2009 at 20:04

JaakkoK

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Comments

dplante · Accepted Answer · 2012-05-26 08:40:28Z

1

Maybe because size is not initialized. Also, you would need to make sure size is less than maxSize.

edited May 26, 2012 at 8:40

dplante

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answered Nov 19, 2009 at 20:08

VNarasimhaM

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