二进制“==”：未找到采用“Enemy”类型左侧操作数的运算符（或没有可接受的转换）

Question

I'm making a game and I'm trying to find enemies with the bool shouldDie == true. I have an Enemy std::list and personally I have no idea what's wrong with the code. If an enemy has shouldDie == true I'll just have an animation playing. Hopefully you can help me understand why I get the error.

Also I have no overloaded == operator, I've searched online and I'm not sure if it's necessary...

bool foundEnemy(Enemy& enemy)
{
    return enemy.shouldDie == true;
}

void Enemy::PlayDeathAnimation(std::list<Enemy>& enemies)
{
    dead = true;

    auto it = std::find_if(enemies.begin(), enemies.end(), foundEnemy); // where I think the error is
    auto enemy = std::next(it, 0);

    if (animationClock.getElapsedTime().asSeconds() >= 0.05f)
    {
        enemy->icon.setTextureRect(animationFrames[animationCounter]);
        if (animationCounter >= 8)
        {
            enemies.remove(*enemy);
        }
        animationCounter++;
        animationClock.restart();

    }
}

class Enemy : public Entity
{
public:
    Enemy() {}
    Enemy(sf::Vector2f position, sf::Texture* texture,Player* target);
    ~Enemy();

    void Update(sf::RenderWindow* window, float tElapsedTime);
    void Draw(sf::RenderWindow* window);
    void Fire(float tElapsedTime);
    void CheckBullets();
    void CheckEnemyBullets();
    void CheckHealth();

    void SetPosition(float x, float y);

    bool shouldDie = false;

    void PlayDeathAnimation(std::list<Enemy>& enemies);



private:

    bool dead = false;

    sf::Texture* deathSpriteSheet;
    std::vector<sf::IntRect> animationFrames;

    std::vector<Bullet> bullets;
    sf::RectangleShape origin;
    sf::RectangleShape aim;
    Player* target;

    int animationCounter = 0;
    sf::Clock animationClock;

};

Answer 1

The error is actually not where you think it is, but few lines below.

if (animationCounter >= 8)
{
    enemies.remove(*enemy); // here
}

You are using std::list::remove function, which will search for any elements of the list matching given element and removes those. To know which element is the same as given, it needs to know how to compare them, thus the need for operator ==

Use std::list::erase() instead - this function accepts an iterator and will remove exact element you point to.

if (animationCounter >= 8)
{
    enemies.erase(enemy); // no dereference of the iterator
}

---

Side note - compiler is very useful tool. If it detects an error, it will point you to a direct line and column where it occurred, although sometimes this piece of information is very well hidden in a ton of other (less useful) prints.

If you don't understand the language of the compiler (yet), you can copy and paste the whole error message into your SO question, this will help us diagnose error faster.