pointer allocation in c++

Question

1.00/5 (1 vote)

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i want to implement something like this

C++

#include "StdAfx.h"
#include<iomanip>
#include <iostream>

using namespace std;

class node
{
	int data;
public:
	node *next;
	node(int d);
};
node::node(int d)
{
	data=d;
}

class Linklist
{
	node *start;
	node *next;
public:
	Linklist();
	void append(int d);
};
Linklist::Linklist()
{
	start=NULL;
}
void Linklist::append(int d)
{
	node *ptr=new node(d);
	ptr->next=NULL;
	start=ptr;
}
int main()
{
	Linklist l;
	l.append(10);
	l.append(20);
	return 0;
}

the pointer ptr at append() is assigned to same address every time , why? and what to do to solve it?

Posted 6-Jul-13 7:13am

bhawin parkeria

Updated 6-Jul-13 8:27am

v3

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Comments

Richard MacCutchan 6-Jul-13 13:21pm

It's a bit of a jumble of random code; you should try writing out exactly what each part should do before you start coding. And make use of the proper syntax for using pointers.

Richard MacCutchan 7-Jul-13 4:09am

Your append() function destroys the previous contents of start instead of linking the new node into the chain. Try my previous comment and think more carefully about the logic of each step. Try drawing a picture of a linked list with three or four elements and see how they should be connected, and how that can be achieved with pointers.

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Sergey Alexandrovich Kryukov · Answer 1 · 2013-07-06T07:29:00

Solution 1

First big design mistake I can see is: remove all I/O from all class members, otherwise, what are you creating, a class which can only work with cin and cout, nothing else?

[EDIT]

As to your question: ptr1 does not have to be assigned to the same address, as it is assigned to a freshly allocated memory location. It can be the case if you repeat allocation and deletion several times, so next allocation simply takes the piece of memory you just deallocated. It's not clear why do you do it in your code. You should review it.

—SA

Posted 6-Jul-13 7:29am

Sergey Alexandrovich Kryukov

Updated 6-Jul-13 7:47am

v2

Comments

bhawin parkeria 6-Jul-13 13:31pm

thanks a lot i will edit this soon

Sergey Alexandrovich Kryukov 6-Jul-13 13:42pm

Very good.
—SA

bhawin parkeria 6-Jul-13 14:05pm

@Sergey :- i have edited the question, now i debugged it and found that ptr has same address everytime.

Sergey Alexandrovich Kryukov 6-Jul-13 15:23pm

All right, I here you. By why doing so? I already explained why it happens...
—SA

bhawin parkeria 7-Jul-13 7:42am

i am confused?
what to do to point to new memory location everytime?
is this again a design problem?

Sergey Alexandrovich Kryukov 7-Jul-13 22:16pm

Wrong question. You see, you already removed the code in question... Think logically: the method in question was to add or insert new element. It means that you cannot deallocate anything. You should have allocated a new element and insert it accordingly.
—SA