error in implementing stack using linked list

Question

I'm trying to implement a stack using linked list in cpp. I'm using class to make the linked list but I'm getting the following error and I dont understand why

#include <bits/stdc++.h>
using namespace std;

class Stack{
    public:
    int top;
    Stack* next;
    Stack(int data){ //constructor
        top = data;
        next = NULL;
    }
    void push(Stack* &head, int data);
    int pop(Stack* &head);
    bool empty(Stack* &head);
};

void Stack::push(Stack* &head, int data){
    Stack* s = new Stack(data);
    s->next = head;
    head = s;
}

int pop(Stack* &head){
    int x = head->top;
    head = head->next;
    return x;
}

bool empty(Stack* &head){
    if(head == NULL)
        return true;
    return false;
}

int main() {
        class Stack* s = new Stack(1);
        s.push(2);
        s.push(3);
        cout << s.empty(s) << endl;
        cout << s.pop(s) << endl;
        cout << s.pop(s) << endl;
        cout << s.pop(s) << endl;
        cout << s.empty(s) << endl;
}

ERROR: request for member 'push' in 's', which is of pointer type 'Stack*' (maybe you meant to use '->' ?)

request for member 'empty' in 's', which is of pointer type 'Stack*' (maybe you meant to use '->' ?)

request for member 'pop' in 's', which is of pointer type 'Stack*' (maybe you meant to use '->' ?)

When I used -> instead of . it said undefined reference to Stack::empty(Stack*&) and undefined reference to Stack::pop(Stack*&)

EDIT: I used -> instead of . and added Stack:: to pop and empty function and it worked but the constructor isn't working

The first set of errors are typos that you've fixed. Why are you asking about them? They do not belong in a [mre]. The second issue (undefined reference) is a common dup, because you've defniied `pop` and `empty` as global functions (and not members, like `push` is). — 1201ProgramAlarm, May 25 '20 at 16:03

score 1 · Answer 1 · answered May 25 '20 at 15:56

As the error message says, when you have a Stack*, you need to use ->, and not ., like this:

s->push(s, 42);
s->empty(s);
// etc

However, you probably don't need a Stack* here at all, and could just use a regular Stack object.

Also, your member functions that are defined outside the class, need to be qualified with the name of the class. So you need:

bool Stack::empty(Stack* &head){

instead of:

bool empty(Stack* &head){

like you have already done for the Stack::push method.

score 0 · Answer 2 · answered May 25 '20 at 15:56

0

You 'accidentally' declared a pointer. Change your code like this

int main()
{
    Stack s(1);
    s.push(2);
    ...

answered May 25 '20 at 15:56

john

85,011
4
57
81

score 0 · Accepted Answer · answered May 25 '20 at 16:00

0

Use -> whenever you are accessing data member of structure pointed by a Pointer. In your case, try using -> instead of . on s in the main function () So, either do

Stack s; 
s.push(1);

Or

Stack* s;
s->push(s,1);

answered May 25 '20 at 16:00

Abhishek Bhagate

5,583
3
15
32

`Stack* s; s->push(s,1);` — This is undefined behavior. – Daniel Langr May 25 '20 at 16:04

error in implementing stack using linked list

3 Answers3