print out an pointer array from a double pointer function in main

Question

This is from my .hpp file.

struct Item{
    std::string todo;};
const int MAX_STACK_SIZE = 5;
class StackArray
{
    public:
        StackArray();
        bool isEmpty();
        bool isFull();
        void push(std::string Item);
        void pop();
        Item* peek();
        int getStackTop() { return stackTop; }
        Item** getStack() { return stack; }
    private:
        int stackTop;
        Item* stack[MAX_STACK_SIZE];
};
#endif

And the following is part function from my .cpp file.

void StackArray::push(std::string Item)
{
    if (isFull())
    {
        cout<<"Stack full, cannot add new todo item."<<endl;
    }
    else
    {
        stackTop++;
        Item* newStack = new Item[MAX_STACK_SIZE];
        newStack[stackTop].todo = Item;
    }
}

I really confused about printing out the stack array in main.cpp file. How can I do that? Here is now I got, but can only print out the address.

int main()
{
    StackArray stackArray;
    if (stackArray.isEmpty())
        cout<< "Empty stack." <<endl;
    stackArray.push("25");
    stackArray.push("20");
    stackArray.push("15");
    stackArray.push("10");

    Item**stack1=new Item*[5];
    *stack1=new Item;
    stack1=stackArray.getStack();
    for(int i=0;i<5;i++)
    {
        cout<<*(stack1+i)<<endl;
    }
}

You're never saving newStack anywhere permanent, so you're leaking memory. — Barmar
– Barmar, Commented Oct 13, 2017 at 22:26
cout<<stack1[i]->todo; Except that it'll probably crash, because you never in fact initialize the contents of StackArray::stack; it contains random garbage. — Igor Tandetnik
– Igor Tandetnik, Commented Oct 13, 2017 at 22:28
Do I need to delete old stack after I assigned newStack in that function? — Justin w
– Justin w, Commented Oct 13, 2017 at 22:33

Barmar · Accepted Answer · 2017-10-13 22:32:46Z

1

Your push method is never actually adding anything to the stack. It's allocating an entirely new array of pointers, but it's only assigned to a local variable, which goes away when the function ends. It should be adding the item to stack.

void TodoStackArray::push(std::string Item)
{
    if (isFull())
    {
        cout<<"Stack full, cannot add new todo item."<<endl;
    }
    else
    {
        stackTop++;
        stack[stackTop] = new Item;
        stack[stackTop]->todo = Item;
    }
}

To print out the items, you need to indirect through the pointers.

for (int i = 0; i < 5; i++) {
    cout << stack1[i]->todo << '\n';
}

answered Oct 13, 2017 at 22:32

Barmar

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