Virtual methods and overriding [duplicate] - c++

Question

This question already has answers here:
What is object slicing?
(18 answers)
Range based loop: get item by value or reference to const?
(5 answers)
Closed 10 months ago.
What am I doing?
I'm trying to do some basic inheritance for the game I'm working on. The idea is to have a base Entity class that the Player will inherit from. The Entity class has a virtual update or think method that each child will override to fit it's needs.
This is how the engine handles the update loop:
void Engine::update() {
for (Entity entity : entities) {
entity.update(deltaTime);
}
}
The code:
Entity.hpp
#pragma once
#include "Position.hpp"
#include "AssetManager.hpp"
#include "Logger.hpp"
#define SPATIAL 1
#define VISUAL 1 << 1
class Entity {
public:
Entity(Position *position, const char *visualPath);
int flags;
const char *visualPath;
Position position;
virtual void update(float deltaTime);
};
Entity.cpp
#include "Entity.hpp"
Entity::Entity(Position *position, const char *visualPath) {
flags = 0;
if (position) {
flags |= SPATIAL;
this->position = *position;
}
if (visualPath) {
flags |= VISUAL;
this->visualPath = visualPath;
}
}
void Entity::update(float deltaTime){
Logger::log("No update method");
};
Player.hpp
#pragma once
#include "../Entity.hpp"
#include "../Logger.hpp"
class Player : public Entity {
public:
Player();
void update(float deltaTime) override;
};
Player.cpp
#include "Player.hpp"
Player::Player() : Entity(new Position(0, 0), "assets/player.png") {}
void Player::update(float deltaTime) {
this->position.x += 10;
Logger::log("Player says hi");
}
What's the issue?
Even tho I have overridden the update method on the Entity within Player, Player still prints "No update method". It seems the override didn't do anything.

Answer 1

Change this:
void Engine::update() {
for (Entity entity : entities) {
entity.update(deltaTime);
}
}
To this:
void Engine::update() {
for (Entity& entity : entities) {
entity.update(deltaTime);
}
}
In the original implementation, your for loop makes a copy of the item in entities. You probably didn't want that, but more importantly, entity is just a copy of the base class, so the derived class information is lost. Pass by reference to avoid this issue and other bugs.