c++ - union 和类(Class)

Question

我有很多空闲时间(圣诞节假期也快到了!)所以，我试图将我的两种爱好结合起来，视频游戏和 C++。它不是真正的视频游戏项目，只是一些使用类的控制台脚本。那么，问题来了；

#include <stdafx.h>
#include <iostream>

class m4a1 {
    public:
        int Damage = 12;
        int Mag = 30;
};

class ak47 {
    public: 
        int Damage = 14;
        int Mag = 24;
};

union Gun_Union {
    m4a1 M4A1_Union;
    ak47 Ak47_Union;
};

class Player {
    public:
        Gun_Union Gun_Player;
        int Health = 200;
};

template <typename Type> 
void Shot(Type* Player_Obj) {
    Player_Obj->Gun_Player->AK47_Union->Mag--;
    Player_Obj->Health = Player_Obj->Health - Player_Obj->Gun_Player->AK47_Union->Damage;
}   
int main() {

    Player Player_Obj;
    Player_Obj.Gun_Player;
    Shot <Player> (&Player_Obj);
    std::cout << Player_Obj.Health;
}

在第 35 行，它给了我错误Player::Player(void) 试图引用消除函数。我发现用 Player 类(第 25 行)中的任何其他类型更改 Gun_Union 不会给我错误。

我也想问一下Player_Obj.Gun_Player = Ak47_Union命令是否可行；抱歉英语不好。

Answer 1

要回答您的原始 问题，您的union 具有非平凡的成员(因为初始值设定项)，但没有构造函数。您需要告诉编译器您最初想要 union 的哪些成员，因为编译器必须构造一个或另一个。这可以通过给 union 一个构造函数来实现。

然后您将混合使用 . 和 -> 运算符。

这是一个可以编译的版本(虽然我不敢称之为“固定”):

#include <iostream>

class m4a1 {
public:
  int Damage = 12;
  int Mag = 30;
};

class ak47 {
public:
  int Damage = 14;
  int Mag = 24;
};

union Gun_Union {
  m4a1 M4A1_Union;
  ak47 Ak47_Union;
  Gun_Union() : Ak47_Union() {}   // <=== the initial state is ak47
};

class Player {
public:
  union Gun_Union Gun_Player;
  int Health = 200;
};

template <typename Type>
void Shot(Type* Player_Obj) {
  Player_Obj->Gun_Player.Ak47_Union.Mag--;
  Player_Obj->Health = Player_Obj->Health - Player_Obj->Gun_Player.Ak47_Union.Damage;
}
int main() {

  Player Player_Obj;
  Player_Obj.Gun_Player;
  Shot <Player>(&Player_Obj);
  std::cout << Player_Obj.Health;
}