InStack.cpp

#include <iostream>

struct Point
{
    double x, y, z;
    Point* next;
};

// WARNING: not thread safe
template <typename T> class InStack
{
private:
    T* stack;

public:
    InStack () : stack(0) {}
    ~InStack ()
    {
        clear();
    }

    void push (T* item)
    {
        item->next = stack;
        stack = item;
    }
    T* pop ()
    {
        T* temp = stack;
        stack = stack->next;
        return temp;
    }
    void clear ()
    {
        while (stack)
        {
            T* temp = stack;
            stack = stack->next;
            delete temp; // Can we assume that new was always used?
        }
    }
    T* top ()
    {
        return stack;
    }
    T* next (T* item)
    {
        return item ? item->next : 0;
    }
    unsigned getLength ()
    {
        unsigned length = 0;
        T* temp = stack;
        while (temp)
        {
            ++length;
            temp = temp->next;
        }
        return length;
    }
};

int main(int argc, char *argv[])
{
    InStack<Point> stack;
    Point* a = new Point;
    Point* b = new Point;
    Point* c = new Point;
    a->x = 10;
    b->x = 20;
    c->x = 30;
    stack.push(&a);
    stack.push(&b);
    stack.push(&c);
    std::cout << "Length: " << stack.getLength() << "\n";
    std::cout << "Top: " << stack.top()->x << "\n";
    std::cout << "next: " << stack.next(stack.top())->x << "\n";
    std::cout << "null.next: " << stack.next(0) << "\n";
    std::cout << "pop: " << stack.pop()->x << "\n";
    std::cout << "pop: " << stack.pop()->x << "\n";
    std::cout << "Length: " << stack.getLength() << "\n";
    stack.push(&c);
    std::cout << "Top: " << stack.top()->x << "\n";
    std::cout << "Length: " << stack.getLength() << "\n";
    stack.clear();
    std::cout << "Length: " << stack.getLength() << "\n";
    return 0;
}