Why are flag enums usually defined with hexadecimal values

c# .net enums enum-flags
Adi Lester picture Adi Lester · Nov 4, 2012 · Viewed 34.9k times · Source

A lot of times I see flag enum declarations that use hexadecimal values. For example:

[Flags]
public enum MyEnum
{
    None  = 0x0,
    Flag1 = 0x1,
    Flag2 = 0x2,
    Flag3 = 0x4,
    Flag4 = 0x8,
    Flag5 = 0x10
}

When I declare an enum, I usually declare it like this:

[Flags]
public enum MyEnum
{
    None  = 0,
    Flag1 = 1,
    Flag2 = 2,
    Flag3 = 4,
    Flag4 = 8,
    Flag5 = 16
}

Is there a reason or rationale to why some people choose to write the value in hexadecimal rather than decimal? The way I see it, it's easier to get confused when using hex values and accidentally write Flag5 = 0x16 instead of Flag5 = 0x10.

Answer

exists-forall picture exists-forall · Nov 4, 2012

Rationales may differ, but an advantage I see is that hexadecimal reminds you: "Okay, we're not dealing with numbers in the arbitrary human-invented world of base ten anymore. We're dealing with bits - the machine's world - and we're gonna play by its rules." Hexadecimal is rarely used unless you're dealing with relatively low-level topics where the memory layout of data matters. Using it hints at the fact that that's the situation we're in now.

Also, i'm not sure about C#, but I know that in C x << y is a valid compile-time constant. Using bit shifts seems the most clear:

[Flags]
public enum MyEnum
{
    None  = 0,
    Flag1 = 1 << 0,
    Flag2 = 1 << 1,
    Flag3 = 1 << 2,
    Flag4 = 1 << 3,
    Flag5 = 1 << 4
}

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