CODEWITHSUNDEEP
c++arrayspointers
Kevin D
Kevin D

Reputation: 177

Error deleting pointer of arrays pointing to arrays C++

I am currently creating a program that simulates a Galton board in C++. I understand how to create a pointer, create an array of pointers, and point each one at another array of ints. My problem is occuring when i try to descruct my pointer array, its telling me:

"Debug Error!

HEAP CORRUPTION DETECTED: after Normal block (#927) at 0x0115E978. CRT detected that the application wrote to memory after end of heap buffer."

I've been banging my head against the wall with this one, as it seems all the examples I can find online have this exact approach. I even rewrote my program into a class to make it more simple. The program runs and does exactly what it's supposed to until the ob1 starts to descruct, which is when the program pukes. I'm stuck.

Here is my code:

#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cstdlib>
#include <ctime>

using namespace std;

class foo
{
public:
    foo();
    foo(int);
    ~foo();
    void allocateSpace();
    void runGame();
    void printResults();
private:
    int bins;
    int** p;
};

foo::foo()
{
    this->bins = 0;
}

foo::foo(int bins)
{
    this->bins = bins; 
    this->p = new int*[bins]; //setting p to array of pointers
}

foo::~foo()
{
     for (int i = 0; i < bins; i++)
     {
         delete[] this->p[i];
     }
     delete[] p;
}

void foo::allocateSpace()
{
    for (int i = 0; i < bins; i++)
    {
        this->p[i] = new int[i]; //creatung an int array of size i at each pointer array cell

        for (int j = 0; j <= i; j++)
        {
            this->p[i][j] = 0;
        }
    }
}

void foo::runGame()
{
    const int numOfRuns = 1000;
    for (int i = 0; i < numOfRuns; i++)
    {
        this->p[0][0]++; //each ball hits the first peg, so always increment it before anything else
        int j = 0; //setting j = 0 sets it to the left
        for (int i = 1; i < bins; i++)
        {
            int rando = rand() % 2;
            if (rando == 1) //move right
            {
                j++;
            }
            this->p[i][j]++;
        }
    }
}

void foo::printResults()
{
    for (int i = 0; i < bins; i++)
    {
        for (int j = 0; j <= i; j++)
        {
            cout << setw(5) << this->p[i][j];
        }
        cout << endl;
    }
}

int main()
{
    srand(time(0));
    int numOfBins;

    cout << "Enter the number of bins: ";
    cin >> numOfBins;
    cout << endl;

    foo ob1(numOfBins);

    for (int i = 0; i < 50; i++)
    {
        ob1.allocateSpace();
        ob1.runGame();
        ob1.printResults();
    }

    system("pause");
    return 0;
}

Any help would be much appreciated.

Upvotes: 1

Views: 307

Answers (1)

jxh
jxh

Reputation: 70402

In allocateSpace, you write beyond the allocated object. This corrupts your heap.

    this->p[i] = new int[i];

    for (int j = 0; j <= i; j++)
    {
        this->p[i][j] = 0;
    }

printResults has a similar problem: You read beyond the allocated object.

Then, in runGame, you attempt to increment a 0 sized object.

    this->p[0][0]++;

The fix:

It seems you need to increase your allocation by 1.

    this->p[i] = new int[i+1];

This will avoid the heap corruption issue. You still have a memory leak issue, because you allocate new memory on top of your existing memory on each iteration in main().

Your code would be safer if you adopted the use of vector<> instead of managing dynamically allocated arrays.

Upvotes: 2

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