CODEWITHSUNDEEP
c++arraysexception
Nealio
Nealio

Reputation: 5

Memory exception when coding dynamic array C++

I am fairly new to c++, as this is the first class I am taking of it. I am creating a class that will dynamically create/delete an array based on what operations are performed. I am getting this exception when I try to add something to the array I believe. Any help is much appreciated.

Code:

#include "ArrayList.h"
#include < string>

using namespace std;

int count = 0;

 ArrayList::ArrayList(){
Object *items = new Object[count];
items[0] = "NULL";
}    

 ArrayList::~ArrayList(){
 releaseList();
 }

void ArrayList::releaseList(){
delete[] items;
count = 0;
ArrayList();
}

void ArrayList::add(Object o){
Object *temp = new Object[count + 1];
for(int i = 0; i < count; i ++){
    temp[i] = items[i];
}
temp[count + 1] = o;
delete[] items;
items = temp;
delete[] temp;
count = count + 1;
}

void ArrayList::add(Object o, int index){
Object *temp = new Object[count + 1];
for(int i = 0; i < index; i++){
    temp[i] = items[i];
}
temp[index] = o;
for(int i = index + 1; i < count -1; i ++){
    temp[i] = items[i];
}
delete[] items;
items = temp;
delete[] temp;
count = count + 1;
}

The .h file for ArrayList

#ifndef ARRAY_LIST_H
#define ARRAY_LIST_H

#include <string>
using namespace std;

typedef string Object;


class ArrayList {
private:
Object *items;      // a dynamic array of pointers to Objects
int numberOfItems;

// Releases all the memory allocated to the list; resets the object to its
// default values.
void releaseList();

public:
// Initializes object to default values (NULL, 0).
ArrayList();

// Destroys the object. Calls releaseList() to do the actual work.
~ArrayList();

// Appends the object o to the end of the list. This resizes the array by 1.
void add(Object o);

// Adds the object o and the specified index. This resizes the array by 1.
void add(Object o, int index);

// Removes all the items from the list. Resets object to its default state.
void clear();

// Returns true if the list contains the object o.
bool contains(Object o) const;

// Returns the object at the specified index. Assumes index is in range.
Object objectAt(int index) const;

// Returns the index of the first matching object o. Assumes the object is in the list.
int indexOf(Object o) const;

// Returns the index of the last matching object. Assumes the object is in the         list.
int lastIndexOf(Object o) const;

// Returns true if list is empty.
bool isEmpty() const;

// Removes the object o from the list. List is resized. Assumes object is present.
void remove(Object o);

// Removes the object o at the specified index. List is resized. Assumes index is in range.
void remove(int index);

// Returns the number of elements in the list.
int size() const;

// Sets the element at the specified index.
void set(Object o, int index);

// Returns a string containing all the items comma separated and surrounded
// by curly ({) braces, i.e. {item1, item2, ...}
string toString();
};

#endif

Upvotes: 0

Views: 661

Answers (1)

Matt Phillips
Matt Phillips

Reputation: 9691

This is a problem, in ArrayList::add, that will throw an access violation exception:

Object *temp = new Object[count + 1];
...
temp[count + 1] = o;

You're assigning an object to a memory location one past the end of the array. C++ is zero-indexed, meaning if you have

int A = new int[5];

then valid locations are A[0] ... A[4], but not A[5].

Upvotes: 3

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