枚举中的整数溢出，仅循环命名整数

问题描述

我怎样才能实现这种行为？

enum week {
    sunday=0,monday,tuesday,wednesday,thursday,friday,saturday
};

enum week day = saturday; // 6
// ++day => 0

enum week day = sunday; // 0
// --day => 6

解决方法

您可以使用枚举类并为其重载运算符（如@NathanOliver 所建议的那样）。 @Thomas Matthews 建议的公式可用于避免处理负数：

枚举 + 运算符实现

week 被重命名为 day 以避免混淆（一个枚举值不代表一整周，只代表一天）

enum class day : unsigned char {
    sunday = 0,monday,tuesday,wednesday,thursday,friday,saturday
};

// preincrement
day& operator++(day& d)
{
    d = static_cast<day>((static_cast<unsigned char>(d) + 1) % 7);
    return d;
}

// postincrement
day operator++(day& d,int)
{
    day res = d;
    d = static_cast<day>((static_cast<unsigned char>(d) + 1) % 7);
    return res;
}

// predecrement
day& operator--(day& d)
{
    d = static_cast<day>((static_cast<unsigned char>(d) + 6) % 7);
    return d;
}

// postdecrement
day operator--(day& d,int)
{
    day res = d;
    d = static_cast<day>((static_cast<unsigned char>(d) + 6) % 7);
    return res;
}

测试代码

std::ostream& operator<<(std::ostream& s,day d)
{
    switch (d)
    {
    case day::monday:
        s << "Monday";
        break;
    case day::tuesday:
        s << "Tuesday";
        break;
    case day::wednesday:
        s << "Wednesday";
        break;
    case day::thursday:
        s << "Thursday";
        break;
    case day::friday:
        s << "Friday";
        break;
    case day::saturday:
        s << "Saturday";
        break;
    case day::sunday:
        s << "Sunday";
        break;
    }
    return s; 
}

int main() {
    day d1 = day::sunday;
    --d1;

    day d2 = day::saturday;
    ++d2;

    day d3 = day::wednesday;
    --d3;

    day d4 = day::wednesday;
    ++d4;

    std::cout << d1 << '\n'
        << d2 << '\n'
        << d3 << '\n'
        << d4 << '\n';


    return 0;
}

输出：

Saturday
Sunday
Tuesday
Thursday