C++ how to reach 'stack' behaviour in this code? - c++

Question

I would like to ask 2 question about this code. Where I just try to simulate a stack.
Stack.h
#pragma once
namespace stackandqueue {
class Stack
{
private:
int index;
int *stackdata;
public:
Stack();
~Stack();
void push(int val);
int pop();
int top();
bool isEmpty();
};
}
Stack.cpp
#include "stdafx.h"
#include "Stack.h"
namespace stackandqueue {
Stack::Stack() : index{ 0 }
{
stackdata = new int[index];
}
Stack::~Stack()
{
delete[] &stackdata;
}
void Stack::push(int val) {
stackdata[index] = val;
index++;
}
int Stack::pop() {
int val = stackdata[index];
index--;
return val;
}
int Stack::top() {
return stackdata[index];
}
bool Stack::isEmpty() {
return index == 0;
}
}
Meaning is to let me create
Stack stack;
And then it initilizes a dynamic array with 0 as first index and that let me push, pop, top values.
First question:
Why am I having unresolved symbols for method definitions?
Second question:
About 'stackdata', you find is the right way if I want to declare an "array" with dynamic size for this behaviour?
I'm open for improvements and best practices. Im used to programming languagesbut I've never delved into c ++ and I don't want to have bad practices. So you see I am taking it from the begining.
Thanks.
I post solution reached with your help that maybe helps someone.
class Stack
{
private:
int index;
int* stackdata;
public:
Stack(int size);
~Stack();
void push(int val);
int pop();
int top();
bool isEmpty();
};
Stack::Stack(int size)
: index {0}, stackdata{new int[size]}
{
}
Stack::~Stack()
{
delete[] stackdata;
}
void Stack::push(int val) {
stackdata[index] = val;
index++;
}
int Stack::pop() {
index--;
return stackdata[index];
}
int Stack::top() {
return stackdata[index-1];
}
bool Stack::isEmpty() {
return index == 0;
}

Answer 1

There are several problems with this.
An array, dynamically allocated or otherwise, is not a stack/queue/vector. You're creating literally 0 ints. All of your element accesses after that have undefined behaviour. You need your array to grow, i.e. be a vector, e.g. std::vector.
delete[] &stackdata has the wrong level of indirection. You meant delete[] stackdata. You were trying to delete the pointer which was not dynamically allocated.
You're missing copy/move constructors and copy/move assignment operators so as soon as you transport a Stack anywhere it will explode. (The original instance will do a delete[] on the same pointer that the copied/moved instances will!) Read about the rule of three/five/zero.
Other than that, it looks like a stack.
The problem you don't have here is an undefined reference, which is funny because that's the only one you asked about. :) If you do indeed have such a thing, it's likely a problem with your build system (failing to compile that source file), which we cannot see.