Object has type qualifiers that are not compatible

问题:

My class Game has a member EntityManager entityManager_.

The class EntityManager has a private member Player player_ and the public getter function Player &EntityManager::getPlayer() which returns player_.

The class Player has for example the functions void startMoving() and sf::Vector2f getPosition() const.

Now, I can without problems call entityManager_.getPlayer().startMoving(); from within my Game class, but when I try for example the following code to get the player's position:

sf::Vector2f playerPosition = entityManager_.getPlayer().getPosition();

I get the following error:

IntelliSense:

EntityManager Game::entityManager_

Error: the object has type qualifiers that are not compatible with the member function

object type is: const EntityManager

Output:

game.cpp(261): error C2662: 'EntityManager::getPlayer' : cannot convert 'this' pointer from 'const EntityManager' to 'EntityManager &'
          Conversion loses qualifiers

I tried removing the const from the player's getPosition function but nothing changed.

I know it probably has something to do with the const but I can't figure out what to change! Could someone please help me?

回答1:

The error message is quite explicit:

game.cpp(261): error C2662: 'EntityManager::getPlayer' : 
               cannot convert 'this' pointer from 'const EntityManager' to 
                                                  'EntityManager &'
          Conversion loses qualifiers

In the context where you are calling getPlayer the object/reference is const. You cannot call a non-const member function on a const object or through a const reference or pointer to const.

Because the error refers to this, the most likely reason is that this code is inside a member function that is const.