C++ Pop Function Linked List - c++

Question

I am writing a program that implements stacks as linked lists. The program complies but when I run it, it crashes. I ran the debugger and says unhandled exception when it gets inside the Pop() function and to the line "topPtr = topPtr->next". I was wondering if anyone noticed something in there that is causing this error. I attached the portion of main and the pop function that I believe i sbeing affected. thanks
template<class ItemType>
struct NodeType
{
ItemType info;
NodeType* next;
};
template<class ItemType>
class Stack
{
private:
int stacklength;
NodeType<ItemType>* topPtr; // It points to a singly-linked list
public:
void Pop(ItemType &x);
template<class ItemType>
void Stack<ItemType>::Pop(ItemType &x)
{
NodeType<ItemType>* tempPtr;
tempPtr = topPtr;
topPtr = topPtr->next;
delete tempPtr;
stacklength--;
}
int main()
{
Stack <int> IntStack;
int x;
IntStack.Pop(x);
}

Answer 1

First off, you don't initialize your pointers.
template<class ItemType>
struct NodeType
{
//...
NodeType() : next(nullptr) {} ///Initialize next so we can check for null
};
template<class ItemType>
class Stack
{
public:
Stack() : topPtr(nullptr), stacklength(0) { } ///initialize
//...
Then, in your Pop, you need to check for an empty stack (you can't pop if there are no elements).
template<class ItemType>
void Stack<ItemType>::Pop(ItemType &x)
{
if (!topPtr)
{
//Here, we need to decide how to handle this.
//One way would be to throw an exception,
//another way would be to change the method signature
//and return a bool.
}
///...
}