Insert and Attach Functions for a Sequence Array Assignment

[natekelsey]

This is my constructor that I'm using:

//PARAMETERIZED CONSTRUCTOR
//sequence(int initial_capacity = DEFAULT_CAPACITY)
//Postcondition: The sequence has been initialized as an empty sequence.
//The insert/attach functions will work efficiently (without allocating
//new memory) until this capacity is reached.
sequence::sequence(int initial_capacity)
	{
		data = new value_type[initial_capacity];
		capacity = initial_capacity;
		used = 0;
	}

I've been coming up with this error for my attach function:
Unhandled exception at 0x00e34008 in Sequence2.exe: 0xC0000005:
Access violation writing location 0x66dcadd8.

// void attach(const value_type& entry)
// Postcondition: A new copy of entry has been inserted in the sequence after
// the current item. If there was no current item, then the new entry has 
// been attached to the end of the sequence. In either case, the newly
// inserted item is now the current item of the sequence.
void sequence::attach(const value_type& entry)
{
	for(int i = used; i < capacity; i++)
	{
		data[i] = data[i+1];
		used++;
		data[current_index] = entry;
	}

}

and this error for my insert function:
Unhandled exception at 0x01053f5a in Sequence2.exe: 0xC0000005:
Access violation writing location 0x6679add8.

// void insert(const value_type& entry)
// Postcondition: A new copy of entry has been inserted in the sequence
// before the current item. If there was no current item, then the new entry 
// has been inserted at the front of the sequence. In either case, the newly
// inserted item is now the current item of the sequence.

void sequence::insert(const value_type& entry)
{
	for(int i = used; i < capacity; i++)
	{
		data[i] = data[i+1];
		used++;
	}
	data[current_index] = entry;
}

Maybe I just have it typed completely wrong or I'm over-thinking/under-thinking these two functions. Advice is appreciated.

[vlad from moscow]

I do not understand what funcrion attach does. But in any case there is no element with index equal to capacity in array data.

void sequence::attach(const value_type& entry)
{
	for(int i = used; i < capacity; i++)
	{
		data[i] = data[i+1];
		used++;
		data[current_index] = entry;
	}

}

The same is valid and for the second function.

[vlad from moscow]

That it would be more clear when i == capacity - 1 that is i < capacity then i + 1 is equal to capacity. However valid indexes for data are 0 - capacity - 1.

[natekelsey]

Not sure if I understand what you're saying. Do you mean something like this:

for(int i = capacity-1; i < capacity;i++)

[natekelsey]

The insert function inserts a value into the sequence before the current index of the array. The attach function is suppose to insert it after the current index of the array.

[vlad from moscow]

Look here

	for(int i = used; i < capacity; i++)
	{
		data[i] = data[i+1];
		used++;
	}

When i is equal to capacity - 1 you are trying to access the element with index i + 1 that is equal to capacity. You have no such an element with index equal to capacity in the array.

[vlad from moscow]

Also it is not clear from your code what is current_index. At least I do not see that you would initialize such data member in the constructor.

[natekelsey]

value_type sequence::current() const
{
	is_item();
	return data[current_index];
}

void sequence::start()
{
	// Current index equals the 1st element on the array
	current_index = data[0];
}

The current_index starts at data[0] and as the user inserts/attaches an element to the array the current_index is suppose to adjust accordingly.

[vlad from moscow]

1) I do not see where current is defined. 2) it seems that this code current_index = data[0]; is simply a stupidy.

[natekelsey]

Oh I forgot to initialize current_index in my constructor as 0.