My struct type is not recognized within my class

Question

Guys, I’m implementing a stack with C++ pointers and have the following code for now:

template <class T>
struct Node {
    T item;
    Node *prox;
};

class Pilha {
    private:
    int tamanho;
    Node *topo;

    public:
    Pilha() {
    this->topo=NULL;
    this->tamanho=0;    
}

In the private attribute top, the guy Node is not being recognized within my class Stack. The eclipse returns the following error: Type 'Node' could not be resolved.

What can it be? Thank you!

Answer 1

The problem is that its structure Node has a template, which will be used to create a Node of any kind, so you must also use this pattern in the class Pilha for the compiler to know what type of Node may vary:

template <class T>
struct Node {
    T item;
    Node *prox;
};

template <class T> // indicação que esta classe tambem usa template
class Pilha {
private:
    int tamanho;
    Node<T> *topo; //aqui o Node é indicado com <T> 

public:
    Pilha() {
        this->topo=NULL;
        this->tamanho=0;
    }
};

In the code above, I only commented on the places I changed.

Note that when instantiating a node you have to use the template notation. Example:

Node<T> *novoNo = new Node<T>();

In c++ also has a better alternative to NULL that is nullptr and which is a pointer literal and avoids some implicit conversions that in certain situations generate problems.