[C++] enum classの要素数を取得する方法

#include <iostream>
enum class Color {
    Red,
    Green,
    Blue,
    Count // 要素数を表すダミーの要素
};
int main() {
    std::cout << "Color enum class has " << static_cast<int>(Color::Count) << " elements." << std::endl;
    return 0;
}

Color enum class has 3 elements.

#include <iostream>
#include <type_traits>
template <typename E>
constexpr auto to_underlying(E e) noexcept {
    return static_cast<std::underlying_type_t<E>>(e);
}
template <typename E>
constexpr size_t enum_size() {
    return to_underlying(E::Count);
}
enum class Fruit {
    Apple,
    Banana,
    Cherry,
    Count // 要素数を表すダミーの要素
};
int main() {
    std::cout << "Fruit enum class has " << enum_size<Fruit>() << " elements."
              << std::endl;
    return 0;
}

Fruit enum class has 3 elements.

#include <array>
#include <iostream>
enum class Animal {
    Dog,
    Cat,
    Bird,
    Count // 要素数を表すダミーの要素
};
int main() {
    constexpr std::array<Animal, static_cast<size_t>(Animal::Count)> animals = {
        Animal::Dog, Animal::Cat, Animal::Bird};
    std::cout << "Animal enum class has " << std::size(animals) << " elements."
              << std::endl;
    return 0;
}

Animal enum class has 3 elements.

#include <iostream>
enum class Day {
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday,
    Count // 要素数を表すダミーの要素
};
int main() {
    for (int i = 0; i < static_cast<int>(Day::Count); ++i) {
        std::cout << "Day " << i << std::endl;
    }
    return 0;
}

Day 0
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6

#include <iostream>
#include <array>
enum class Status {
    Active,
    Inactive,
    Pending,
    Count // 要素数を表すダミーの要素
};
int main() {
    std::array<int, static_cast<size_t>(Status::Count)> statusArray = {1, 0, -1};
    for (size_t i = 0; i < statusArray.size(); ++i) {
        std::cout << "Status " << i << ": " << statusArray[i] << std::endl;
    }
    return 0;
}

Status 0: 1
Status 1: 0
Status 2: -1

#include <iostream>
enum class Level {
    Low,
    Medium,
    High,
    Count // 要素数を表すダミーの要素
};
bool isValidLevel(int level) {
    return level >= 0 && level < static_cast<int>(Level::Count);
}
int main() {
    int inputLevel = 2; // ユーザーからの入力値を想定
    if (isValidLevel(inputLevel)) {
        std::cout << "Valid level: " << inputLevel << std::endl;
    } else {
        std::cout << "Invalid level: " << inputLevel << std::endl;
    }
    return 0;
}

Valid level: 2