What's wrong with my destructor?

Question

// Sparse Array Assignment.cpp : Defines the entry point for the console application.  
//  

#include "stdafx.h"  
#include<iostream>  
using namespace std;  
struct node{  
    int row;  
    int col;  
    int value;  
    node* next_in_row;  
    node* next_in_col;  
};  
class MultiLinkedListSparseArray {  
private:  
    char *logfile;  
    node** rowPtr;  
    node** colPtr; // used in constructor  
    node* find_node(node* out);  
    node* ins_node(node* ins,int col);  
    node* in_node(node* ins,node* z);  
    node* get(node* in,int row,int col);  
    bool exist(node* so,int row,int col);  
    node* dummy;  
    int rowd,cold;  
    //add anything you need  
public:  
    MultiLinkedListSparseArray(int rows, int cols);  
    ~MultiLinkedListSparseArray();  
    void setCell(int row, int col, int value);  
    int getCell(int row, int col);  
    void display();  
    void log(char *s);  
    void dump();  
};  
MultiLinkedListSparseArray::MultiLinkedListSparseArray(int rows,int cols){  
    rowPtr=new node* [rows+1];  
    colPtr=new node* [cols+1];  
    for(int n=0;n<=rows;n++)  
        rowPtr[n]=NULL;  
    for(int i=0;i<=cols;i++)  
        colPtr[i]=NULL;  
    rowd=rows;cold=cols;  
}  
MultiLinkedListSparseArray::~MultiLinkedListSparseArray(){  
    cout<<"array is deleted"<<endl;  
    for(int i=rowd;i>=0;i--){  
        for(int j=cold;j>=0;j--){  
            if(exist(rowPtr[i],i,j))  
                delete get(rowPtr[i],i,j);  
        }  
    }              // it stops in the last loop & doesnt show the done word
    cout<<"done"<<endl;  
    delete [] rowPtr;  
    delete [] colPtr;  
    delete dummy;  
}  
void MultiLinkedListSparseArray::log(char *s){  
    logfile=s;  
}  
void MultiLinkedListSparseArray::setCell(int row,int col,int value){  
    if(exist(rowPtr[row],row,col)){  
        (*get(rowPtr[row],row,col)).value=value;  
    }  
    else{  
        if(rowPtr[row]==NULL){  
            rowPtr[row]=new node;  
            (*rowPtr[row]).value=value;  
            (*rowPtr[row]).row=row;  
            (*rowPtr[row]).col=col;  
            (*rowPtr[row]).next_in_row=NULL;  
            (*rowPtr[row]).next_in_col=NULL;  
        }  
        else if((*find_node(rowPtr[row])).col<col){  
            node* out;  
            out=find_node(rowPtr[row]);  
            (*out).next_in_row=new node;  
            (*((*out).next_in_row)).col=col;  
            (*((*out).next_in_row)).row=row;  
            (*((*out).next_in_row)).value=value;  
            (*((*out).next_in_row)).next_in_row=NULL;  
        }  
        else if((*find_node(rowPtr[row])).col>col){  
            node* ins;  
            ins=in_node(rowPtr[row],ins_node(rowPtr[row],col));  
            node* g=(*ins).next_in_row;  
            (*ins).next_in_row=new node;  
            (*((*ins).next_in_row)).col=col;  
            (*(*ins).next_in_row).row=row;  
            (*(*ins).next_in_row).value=value;  
            (*(*ins).next_in_row).next_in_row=g;  
        }  
    }  
}  
int MultiLinkedListSparseArray::getCell(int row,int col){  
        return (*get(rowPtr[row],row,col)).value;  

}  
void MultiLinkedListSparseArray::display(){  
    for(int i=1;i<=5;i++){  
        for(int j=1;j<=5;j++){  
            if(exist(rowPtr[i],i,j))  
                cout<<(*get(rowPtr[i],i,j)).value<<" ";  
            else cout<<"0"<<" ";  
        }  
        cout<<endl;  
    }  
}  
node* MultiLinkedListSparseArray::find_node(node* out)  
{  
    while((*out).next_in_row!=NULL)  
        out=(*out).next_in_row;  
    return out;  
}  
node* MultiLinkedListSparseArray::ins_node(node* ins,int col){  
    while(!((*ins).col>col))  
        ins=(*ins).next_in_row;  
    return ins;  
}  
node* MultiLinkedListSparseArray::in_node(node* ins,node* z){  
    while((*ins).next_in_row!=z)  
        ins=(*ins).next_in_col;  
    return ins;  
}  
node* MultiLinkedListSparseArray::get(node* in,int row,int col){  
    dummy=new node;  
    dummy->value=0;  
    while((*in).col!=col){  
        if((*in).next_in_row==NULL){  
            return dummy;  
        }  
        in=(*in).next_in_row;  
    }  
    return in;  
}  
bool MultiLinkedListSparseArray::exist(node* so,int row,int col){  
    if(so==NULL)  
        return false;  
    else{  
    while((*so).col!=col){  
        if((*so).next_in_row==NULL)  
            return false;  
        else  
            so=(*so).next_in_row;  
    }  
    return true;  
    }  
}    
int _tmain(int argc, _TCHAR* argv[])
{
    MultiLinkedListSparseArray a(5, 5);
a.setCell(1, 5, 4);
a.setCell(2, 1, 2);
a.setCell(2, 2, 3);
a.setCell(3, 4, 5);
a.setCell(4, 1, 7);
a.setCell(4, 5, 8);
a.setCell(5, 2, 6);
cout << "X[4, 1] = " << a.getCell(4, 1) << endl;
cout << "X[4, 5] = " << a.getCell(4, 5) << endl;
cout << "X[2, 2] = " << a.getCell(2, 2) << endl;
cout << "X[5, 1] = " << a.getCell(5, 1) << endl;
a.display();
a.setCell(3, 4, 0);
a.setCell(1, 5, 0);
cout<<a.getCell(1,5)<<endl;
a.setCell(2, 2, 0);
a.setCell(5, 2, 0);
a.setCell(4, 5, 0);
//a.setCell(2, 5, 7); // problem WHY????????!!!!!!!!!!!!!!!
a.setCell(5, 3, 8);
a.setCell(2, 3, 5);
a.setCell(2, 5, 3);
a.setCell(2, 1, 0);
a.setCell(4, 2, 4);
a.setCell(4, 2, 2);
a.setCell(4, 2, 0);
a.setCell(4, 1, 0);
a.setCell(2, 3, 0);
a.setCell(2, 5, 0);
a.setCell(5, 3, 0);
a.display();
return 0;
}      

Answer 1

Things obviously go wrong, because get method (which, as I assume should be marked as const) makes memory allocation. I don't get the reason why this should be done and you should think about it.

So, your get methods allocates memory for dummy every time it is called (this is a leak). But, what is even worse, if sequence of user actions with your class doesn't have one or more calls to get, your dummy remains simply an uninitialized pointer. Then, when you call your destructor, you will get an error, because you can't dispose memory pointed by a garbage pointer.

Try to rethink, refactor or even rewrite your code.