c++ pointer never initialized still outputs as initialized

Question

All I am doing is declaring a pointer and then checking if its pointing to anything:

#pragma once

#include <Node.h>
#include <stdio.h>

template <class NodeDataType>
class LinkedList
{
typedef Node<NodeDataType>* pNode;

private:    
pNode pHead;


pNode pTail;



public:

void Add(NodeDataType* pNodeTypeData)
{


    if(pHead)
    {
        printf("phead is initialized\n");
    }
    else
    {
        printf("phead is not initialized\n");

    }               
}


};

then, in main(), I am making a new LinkedList object, and calling Add but when i run it, it outputs pHead is initialized ? but i never initialized it?

can someone explain it to me?

thanks

(main)

#include <stdio.h>
#include <LinkedList.h>
#include <GameObject.h>

int main(int argc, char** argv)
{

LinkedList<GameObject> meList;


meList.Add(new GameObject());


return 0;
}

There can be several things wrong here, please post the code in main also so that we can see the error for ourselves — Curious, Jun 15 '17 at 08:24
look at this https://stackoverflow.com/questions/1910832/why-arent-pointers-initialized-with-null-by-default — Andrew Kashpur, Jun 15 '17 at 08:25
Does it ouputs `initialized` or `uninitialized`. Because you never initialize `pHead` but checking it in `if (pHead)`. — Andre Kampling, Jun 15 '17 at 08:32
just outputs: phead is initialized. nothing else, but i after reading what andrew linked it seems to be because c++ apparently just doesn't initialize pointers to null when they are declared, so ill have to do it myself i guess — , Jun 15 '17 at 08:35
Ah sorry I thought you are talking about compiler output, I didn't read it accurately... Now I see it is your output... If you do **not** initialize variables they are uninitialized which means they contain the value that lie at the memory address where the variable lie. It does **not** get overridden by zeroes. This applies for POD types because they don't have a standard constructor like classes. The comment of Andrew Kashpur is pointing also in that direction! — Andre Kampling, Jun 15 '17 at 08:38

nakiya · Accepted Answer · 2017-06-15T08:46:50.093

1

You do not initialise pHead or pTail in constructor or in place. So, these members will have arbitrary values when you create a LinkedList object. So, either write the constructor:

LinkedList()
    :pHead(NULL), pTail(NULL)
{
}

Or initialize them in-place if you are using c++11:

private:    
    pNode pHead = nullptr;
    pNode pTail = nullptr;

edited Jun 15 '17 at 08:46

answered Jun 15 '17 at 08:41

nakiya

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I would also use `nullptr` in the initializer list `:pHead(nullptr), pTail(nullptr)`. – Andre Kampling Jun 15 '17 at 08:43
@AndreKampling : If OP is using C++11, yes. – nakiya Jun 15 '17 at 08:44
1

Yes sure you're right but using at least the `NULL` macro would be more clear then. But he could also provide an own `nullptr` type [see here at SO](https://stackoverflow.com/a/44517878/8051589) if his compiler doesn't support it. – Andre Kampling Jun 15 '17 at 08:46

c++ pointer never initialized still outputs as initialized

1 Answers1