Queue Linked List based implementation in C++

Question

I wrote my implementation to Queue Linked List based. And I need a review for it to improve it and improve my coding skill. I also will put this implementation on my GitHub account.

//======================================================
// Author : Omar_Hafez
// Created : 30 July 2022 (Saturday) 8:02:31 AM
//======================================================
#include <iostream>
#include <memory>
template <class T>
class Queue {
 
 private:
 struct Node {
 T value;
 std::shared_ptr<Node> next;
 Node (T data, std::shared_ptr<Node> ptr) : value(data), next(ptr) {}
 };
 
 int size_value = 0;
 std::shared_ptr<Node> back;
 std::shared_ptr<Node> front;
 public:
 enum QueueOpStatus { FailedQueueEmpty = -1, FailedQueueFull = -2, OK = 1 };
 // this constructor is to keep the consistency with the array based implementation
 Queue(int MAX_SIZE = 1000000) {}
 QueueOpStatus push(T const& t) {
 if(full()) return FailedQueueFull;
 if(front) {
 back->next = std::make_shared<Node>(t, nullptr);
 back = back->next;
 } else {
 front = std::make_shared<Node>(t, nullptr);
 back = front;
 }
 size_value++;
 return OK;
 }
 QueueOpStatus pop() {
 if (empty()) return FailedQueueEmpty;
 front = front->next;
 size_value--;
 return OK;
 }
 bool empty() const { return size_value == 0; }
 bool full() const { return 0; }
 int size() const { return size_value; }
 T top() const { 
 if(empty()) {
 throw "Queue is empty";
 }
 return front->value; 
 }
 void clear() {
 while(!empty()) {
 pop();
 }
 }
};

Answer 1

• push could be streamlined: back will always point to the new node no matter what:

   auto new_node = make_shared<Node>(t, nullptr);
   if (front) {
   back->next = new_node;
   } else {
   front = new_node;
   }
   back = new_node;
  

• The emptiness of the queue is tested differently in push (which tests if (front)) versus pop/top (which tests empty() aka size_value == 0). Technically nothing is wrong, but it gives an uneasy feeling. Better use an uniform test.

• top throwing an exception could be an overkill. Consider returning a std::pair<bool, T>, or std::optional<T>.

• size_value shall be size_t.

• To repeat another review, enqueue/dequeue are far better than push/pop.