枚举类型没有作用域，更喜欢枚举类而不是枚举？

Question

我是 C++ 新手，我想知道是否有人可以帮助我理解为什么

enum difficulty { NOVICE, EASY, NORMAL, HARD, UNBEATABLE };
difficulty myDiffiuclty = EASY

和

enum shipCost { FIGHTER_COST = 25, BOMBER_COST, CRUISER_COST = 50 };
shipCost myShipCost = BOMBER_COST;

有绿色下划线吗？它说它更喜欢枚举类，但是当我将其更改为枚举类时

enum class difficulty { NOVICE, EASY, NORMAL, HARD, UNBEATABLE };
difficulty myDiffiuclty = EASY;

enum class shipCost { FIGHTER_COST = 25, BOMBER_COST, CRUISER_COST = 50 };
shipCost myShipCost = BOMBER_COST;

EASY 变为红色下划线，myShipCost 变为绿色下划线，BOMBER_COST 变为红色下划线，CRUISER_COST 变为红色下划线

const int ALIEN_POINTS = 150;
int aliensKilled = 10;
int score = aliensKilled * ALIEN_POINTS;
cout << "score: " << score << endl;

enum difficulty { NOVICE, EASY, NORMAL, HARD, UNBEATABLE };
difficulty myDifficulty = EASY;

enum shipCost { FIGHTER_COST = 25, BOMBER_COST, CRUISER_COST = 50 };
shipCost myShipCost = BOMBER_COST;
cout << "\nTo upgrade my ship to a cruiser will cost "
    << (CRUISER_COST - myShipCost) << " Resource Points.\n";

system("pause");
return 0;

Answer 1

enum class difficulty { NOVICE, EASY, NORMAL, HARD, UNBEATABLE };
difficulty myDiffiuclty = difficulty::EASY;

enum class shipCost { FIGHTER_COST = 25, BOMBER_COST, CRUISER_COST = 50 };
shipCost myShipCost = shipCost::BOMBER_COST;

使用enum class，删除了与整数的隐式转换，并且您必须确定其中常量的范围。

这被认为是一种改进。显式地将其转换回整数仍然有效，但这并不是偶然发生的。

std::cout << "\nTo upgrade my ship to a cruiser will cost "
    << (static_cast<int>(shipCost::CRUISER_COST) - static_cast<int>(myShipCost)) <<
    " Resource Points.\n";

system("pause");
return 0;

一旦你使用enum class，你应该重命名它们：

enum class difficulty { novice, easy, normal, hard, unbeatable };
difficulty myDiffiuclty = difficulty::easy;

enum class shipCost { fighter =25, bomber=30, cruiser = 50 };
shipCost myShipCost = shipCost::bomber;

由于ship名称的一部分现在位于 中enum，因此无需在常量中重复它。同样，由于名称是有范围的，因此您不必使用SHOUT它们。

但请注意，如果您只是使用它来创建常量而不打算创建类型，请考虑使用类似以下内容的内容：

namespace ship {
  namespace cost {
    constexpr int fighter = 25;
    constexpr int bomber = 30;
    constexpr int cruiser = 50;
  }
}

现在我们有ship::cost::fighter一个编译时计算的 an int，而不是一个enum class。