Access violation reading location 0xCDCDCDD1

Question

I am using Visual Studio 2013. I am getting the Access violation reading location 0xCDCDCDD1 error. References from Wikipedia: Magic Numbers, here, and this question tell me that I am using an uninitialized pointer. I think the problem is with the malloc function I'm using, although I did refer to the CPlusPlus doc before using it.

My code:

#include "SingleNode.h"
#include "SingleList.h"
#include <iostream>
SingleList::SingleList() {}
SingleList::~SingleList() {}
...
    void SingleList::addHead(int value){
    ISingleNode *temp1 = (ISingleNode *)malloc(sizeof(SingleList));
    head = NULL;
    temp1->setValue(value);
    temp1->setNext(head->getNext());
    if (!head->getNext())
    {
        head = temp1;
    }
    else
    {
        temp1->setNext(head->getNext());
        head = temp1;
    }
}

    ...

The error is in the line temp1->setValue(value);

The setValue(int value) function is included from here:

#include "SingleNode.h"
SingleNode::SingleNode() {}
SingleNode::~SingleNode() {}
void SingleNode::setValue(int value){
    this->value = value;
}
int SingleNode::getValue(){
    return value;
}
ISingleNode * SingleNode::getNext(){
    return next;
}
void SingleNode::setNext(ISingleNode * next){
    this->next = next;
}

SingleNode.h:

#pragma once
#include "Interfaces01.h"
class SingleNode :public ISingleNode{
private:
    int value;
    ISingleNode * next = NULL;
public:
    SingleNode();
    ~SingleNode();
    void setValue(int value);
    int getValue();
    ISingleNode * getNext();
    void setNext(ISingleNode * next);
};

SingleList.h:

#pragma once
#include "Interfaces01.h"
class SingleList :public ISingleList{
private:
    int value;
    ISingleNode * head=NULL;
    ISingleNode * temp=NULL;
    ISingleNode * next=NULL;
    ISingleNode * temp1;
public:
    SingleList();
    ~SingleList();
    ISingleNode * getHead();
    void setHead(ISingleNode * head);
    void addHead(int value);
    void orderSort2();
    void orderSort3();
    void sequenceOrderSort();
    void reverse();
    ISingleNode * swap(ISingleNode * head, int k);
    ISingleNode * get_node(ISingleNode * head, int k);
};

On breaking at the line, the debugger is showing me the following values:

Visual Studio 2013 debug values at breakpoint

Why are you use C library calls such as `malloc` in C++ ? – Paul R Sep 15 '14 at 14:34 — Paul R, Sep 15 '14 at 14:34
http://stackoverflow.com/a/127404/487892 – drescherjm Sep 15 '14 at 15:37 — drescherjm, Sep 15 '14 at 15:37

Piotr Skotnicki · Accepted Answer · 2015-06-27T20:45:59.653

Change:

ISingleNode *temp1 = (ISingleNode *)malloc(sizeof(SingleList));

into:

ISingleNode *temp1 = new SingleList;

You are accessing a NULL pointer:

head = NULL; // set to NULL
temp1->setValue(value);
temp1->setNext(head->getNext()); // oops!

you probably meant:

void SingleList::addHead(int value)
{
    ISingleNode *temp1 = new SingleList;
    temp1->setValue(value);
    temp1->setNext(head);
    head = temp1;
}

Access violation reading location 0xCDCDCDD1

1 Answers1