Thread: Problem with vector class (and suggestions)

I'm trying to implement my own version of the stl vector class. I have gotten the push method to work properly, as well as the pop to semi-work. The only problem is when the logical size of the array is less then half of the allotted size for the array. I then try to shorten the size of the array by half. I get a runtime error saying I got a memory access problem on "delete[] dynamic_array;"

Any ideas on why I'm getting the runtime error, as well as suggestions on how I could better improve the class would be greatly appreciated.

Thanks,

cs_student

rofl, I don't know why I didn't post the code, I must of forgot.

Anyways, I'm also planning on implementing a insert method later on.
I'll also be sure to take a look at that library.

Here is the code however,

Code:

#ifndef CONTAINER_H
#define CONTAINER_H


namespace JP
{

template <class Elem> class Container
{
public:

	Container( unsigned int start_size = 10 )
	{
		dynamic_array = new Elem [ start_size ];
		current_size = start_size;
		logical_size = 0;
	}

	void Push( Elem data )
	{
		if( logical_size >= current_size )
		{
			
			temp_array = new Elem[ current_size * 2];

			// Copy dynamic_array to temp_array
			for( unsigned int i = 0; i <= logical_size; i++)
			{
				temp_array[i] = dynamic_array[i];
			}

			current_size *= 2;
			delete[] dynamic_array;
			dynamic_array = new Elem [ current_size ];
			
			dynamic_array = temp_array;
			delete[] temp_array;
		}
		else
		{
			dynamic_array[logical_size] = data;
			logical_size++;
		}
	}
	
	void Pop( unsigned int index )
	{
		if( index <= logical_size )
		{
			for( unsigned int i = index; i <= logical_size - 1; i++)
			{
				dynamic_array[i] = dynamic_array[i+1];
			}

			dynamic_array[logical_size] =  NULL;
			logical_size--;
			
			if( logical_size < current_size / 2 )
			{
				temp_array = new Elem[ current_size / 2 ];

				// Copy dynamic_array to temp_array
				for( unsigned int i = 0; i <= logical_size; i++)
				{
					temp_array[i] = dynamic_array[i];
				}

				current_size /= 2;

				delete[] dynamic_array;     // debugger shows the runtime error occurs on this line
				dynamic_array = new Elem [ current_size ];
				
				dynamic_array = temp_array;
				delete[] temp_array;
			}
		}
	}



private:
	unsigned int	current_size;		// size of array
	unsigned int	logical_size;		// size taken up of array

	Elem * dynamic_array;
	Elem * temp_array;


};

} // namespace JP


#endif // CONTAINER_H


/*********************
container.cpp
*********************/

// Container.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "Container.h"
struct mystruct {
};

mystruct struc, struc2, struc3;
int _tmain(int argc, _TCHAR* argv[])
{
	
	JP::Container< int > MyContainer;
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Pop( 4 );
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Push( 1 );
	MyContainer.Push( 5 );
	MyContainer.Push( 33 );
	MyContainer.Pop( 3 );

	
	return 0;
}

Thank you for your reply.

Firstly, temp_array probably shouldn't be a member of the class, since it will be only used locally in a few functions.

I figured that it would be better to have it locally declared rather than declaring it on the heap every time.

Code:

 Secondly the name Pop suggests removing the last element, which should trivially mean decrementing the logical_size (unless you really want to shrink the array). What you really have there is what (one version of) vector::erase does

I now realize that looking back at previous code I've used (OpenGL).

Please correct me if I'm wrong, or confused, but I thought what I was doing in that section is.

Code:

				// Copy dynamic_array to temp_array
				for( unsigned int i = 0; i <= logical_size; i++)
				{
					temp_array[i] = dynamic_array[i];
				}
				
				current_size /= 2;	// change the current size

				delete[] dynamic_array;     // delete current memory of dynamic_array
				dynamic_array = new Elem [ current_size ];	// allocate new memory to dynamic_array
				
				dynamic_array = temp_array;		// copy temp_array to dynamic_array
				delete[] temp_array;			// delete temp_array

Again thanks for your help,


cs_student

How can I make dynamic_array simply point to the data that temp_array points to?

Example:

Code:

dynamic_array = temp_array;

Right? Is there some secret trick I am not aware of in your question?