the same addresses of different nodes - c++

Question

I try to write a bidirectional list. I must use overloaded operators([] and +=). [] - access to given node. += - add node to my list. I wrote these methods and it looks ok, but it doesn't work and I have no idea why.
here are core lines of my code:
//********************************************************
CLista::CNode* CLista::operator[](int i_index)
{
int i_help = 0;
CNode* c_result = &c_root;
while(i_help < i_index)
{
c_result = c_result->getNext();
i_help++;
}
return c_result;
}
//*********************************************************
void CLista::operator+=(void* pv_object)
{
if(i_numNodes == 0)
{
c_root = CNode(pv_object);
}
else
{
CNode c_new = CNode(pv_object);
CNode* c_help = this->operator[](i_numNodes - 1);
c_new.setPrevious(c_help);
(*c_help).setNext(&c_new);
}
i_numNodes++;
}
int _tmain(int argc, _TCHAR* argv[])
{
CLista list = CLista();
string s1 = string("first");
void* wsk1 = &s1;
string s2 = string("second");
void* wsk2 = &s2;
string s3 = string("third");
void* wsk3 = &s3;
list += wsk1;
list += wsk2;
list += wsk3;
void* res1 = (*list[0]).getObject();
void* res2 = (*list[1]).getObject();
void* res3 = (*list[2]).getObject();
cout << "res1: " << res1 << endl;
cout << "res2: " << res2 << endl;
cout << "res3: " << res3 << endl;
cout << "wsk1:" << wsk1 << endl;
cout << "wsk2:" << wsk2 << endl;
cout << "wsk3:" << wsk3 << endl;
}
and here is header:
class CLista
{
public:
class CNode
{
public:
CNode(void)
{
pc_next = NULL;
pc_previous = NULL;
}
CNode(void* pv_object)
{
pc_next = NULL;
pc_previous = NULL;
this->pv_object = pv_object;
}
CNode* getNext(){return pc_next;};
CNode* getPrevious(){return pc_previous;};
void* getObject(){return pv_object;};
void setNext(CNode* pc_next);
void setPrevious(CNode* pc_previous);
private:
CNode* pc_next;
CNode* pc_previous;
void* pv_object; // czy to jest dobrze?
};
CNode c_root;
int i_numNodes;
public:
CLista(void);
~CLista(void);
CNode* operator[](int index);
void operator+=(void* object);
};
When I add third element to list and then check it, it is strange problem: addresses of res2 and res3 are the same.

Answer 1

In your operator += function, you create a local CNode called c_new that you link into your linked list. When the scope ends (which happens before the function returns), that local is destructed, leaving the list dangling (pointing at a no longer valid CNode, whose memory is about to be reused for some other local variable, such as the next c_new created on the next call to the function).
Using/accessing an object after it has gone out of scope and been destroyed is undefined behavior, so will generally crash or otherwise misbehave.