Question

Here, i am trying to create a Nth level hierarchy but doesnt let me point to outer-class of an inner class and getting an access violation error. But the latter version workes.

What is my mistake? Is this about the scope of newly created inner-loops? But they are created inside the class so it shouldnt be problem should it?

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

#include "stdafx.h"
#include<iostream>
#include<stdlib.h>

class a
{
public:
    int x;
    a * inner;
    a * outer;
    a(int n)   //creates an inner a
    {
        n--;
        x=n;    
        if(n>0){inner=new a(n);}else{inner=NULL;}   
        inner->outer=this;//Unhandled exception at 0x004115ce in atom.exe: 0xC0000005:
                          //Access violation writing location 0x00000008.
    }

};

int main()
{
    a * c=new a(5);
    a * d=c;
    while((d->inner))     //would print 4321 if worked
    {
        std::cout<<d->x;
        d=d->inner;
    }
    getchar();
    delete c;
    d=NULL;
    c=NULL;
    return 0;
}

But this works:

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

#include "stdafx.h"
#include<iostream>
#include<stdlib.h>

class a
{
public:
    int x;
    a * inner;
    a * outer;
    a(int n)   //creates an inner a
    {
        n--;
        x=n;    
        if(n>0){inner=new a(n);inner->outer=this;}else{inner=NULL;} 
        //works without error
    }

};

int main()
{
    a * c=new a(5);
    a * d=c;
    while((d->inner))     //prints 4321
    {
        std::cout<<d->x;
        d=d->inner;
    }
    getchar();
    delete c;
    d=NULL;
    c=NULL;
    return 0;
}

Do you think all they are auto-deletet when i just delete c ?

Answer 1

When you do this:

if(n>0)
{
   inner=new a(n); //first n is 4, then 3,2,1 and then 0
}
else
{
   inner=NULL;
}   
inner->outer=this;

the condition n>0 will eventually not hold (at the 5th call), so inner will be NULL, and then you runt into undefined behavior (and the crash) when you attempt to dereference it (inner->outer).