C# 中长值的枚举

发布于 2024-11-30 07:24:53 字数 473 浏览 0 评论 0原文

为什么这个声明

public enum ECountry : long
{
    None,
    Canada,
    UnitedStates
}

需要对其任何值进行强制转换？

long ID = ECountry.Canada;
// Error Cannot implicitly convert type 'ECountry' to 'long'.
// An explicit conversion exists (are you missing a cast?)

除了强制转换之外，还有其他方法可以直接从枚举中获取 long 值吗？

这也行不通，例如：

public enum ECountry : long
{
    None = 0L,
    Canada = 1L,
    UnitedStates=2L
}

原文

Why does this declaration,

public enum ECountry : long
{
    None,
    Canada,
    UnitedStates
}

require a cast for any of its values?

long ID = ECountry.Canada;
// Error Cannot implicitly convert type 'ECountry' to 'long'.
// An explicit conversion exists (are you missing a cast?)

And is there a way to get a long value directly from the enum, besides casting?

This would not work either, for example:

public enum ECountry : long
{
    None = 0L,
    Canada = 1L,
    UnitedStates=2L
}

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最好是你 2024-12-07 07:24:54

AFAIK，你必须铸造。

MSDN 文章说：

“但是，需要显式转换才能从枚举类型转换为整型”（int 或 long）

您可以查看：

枚举类型（C# 参考）

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热血少△年 2024-12-07 07:24:53

问题是不底层类型仍然是int。它是 long，您可以为成员分配 long 值。但是，您永远不能只将枚举值分配给整型而不进行强制转换。这应该有效：

public enum ECountry : long
{
    None,
    Canada,
    UnitedStates = (long)int.MaxValue + 1;
}

// val will be equal to the *long* value int.MaxValue + 1
long val = (long)ECountry.UnitedStates;

The issue is not that the underlying type is still int. It's long, and you can assign long values to the members. However, you can never just assign an enum value to an integral type without a cast. This should work:

public enum ECountry : long
{
    None,
    Canada,
    UnitedStates = (long)int.MaxValue + 1;
}

// val will be equal to the *long* value int.MaxValue + 1
long val = (long)ECountry.UnitedStates;

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金橙橙 2024-12-07 07:24:53

enum 的默认基础类型是 int。 enum 可以是除 char 之外的任何整型。

如果您希望它很长，您可以执行以下操作：

// Using long enumerators
using System;
public class EnumTest 
{
    enum Range :long {Max = 2147483648L, Min = 255L};
    static void Main() 
    {
        long x = (long)Range.Max;
        long y = (long)Range.Min;
        Console.WriteLine("Max = {0}", x);
        Console.WriteLine("Min = {0}", y);
    }
}

这里最重要的是强制转换。正如 @dlev 所说，在 enum 中使用 long 的目的是支持大量标志（超过 32 个，因为 2^32 是 4294967296，并且 >long 可以容纳超过 2^32)。

The default underlying type of enum is int. An enum can be any integral type except char.

If you want it to be long, you can do something like this:

// Using long enumerators
using System;
public class EnumTest 
{
    enum Range :long {Max = 2147483648L, Min = 255L};
    static void Main() 
    {
        long x = (long)Range.Max;
        long y = (long)Range.Min;
        Console.WriteLine("Max = {0}", x);
        Console.WriteLine("Min = {0}", y);
    }
}

The cast is what is important here. And as @dlev says, the purpose of using long in an enum is to support a large number of flags (more than 32 since 2^32 is 4294967296 and a long can hold more than 2^32).

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旧时模样 2024-12-07 07:24:53

您必须强制转换枚举以从中获取值，否则它将保留枚举类型。

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<逆流佳人身旁 2024-12-07 07:24:53

MSDN：

来自在本例中，基类型选项用于声明一个成员为 long 类型的枚举。请注意，即使枚举的基础类型是 long，枚举成员仍然必须使用强制转换显式转换为 long 类型。

// keyword_enum2.cs
// Using long enumerators
using System;
public class EnumTest
{
    enum Range :long {Max = 2147483648L, Min = 255L};
    static void Main()
    {
        long x = (long)Range.Max;
        long y = (long)Range.Min;
        Console.WriteLine("Max = {0}", x);
        Console.WriteLine("Min = {0}", y);
    }
}

输出
最大值 = 2147483648 最小值 = 255

From MSDN:

In this example, the base-type option is used to declare an enum whose members are of the type long. Notice that even though the underlying type of the enumeration is long, the enumeration members must still be explicitly converted to type long using a cast.

// keyword_enum2.cs
// Using long enumerators
using System;
public class EnumTest
{
    enum Range :long {Max = 2147483648L, Min = 255L};
    static void Main()
    {
        long x = (long)Range.Max;
        long y = (long)Range.Min;
        Console.WriteLine("Max = {0}", x);
        Console.WriteLine("Min = {0}", y);
    }
}