Test that only a single bit is set in Flags Enum [duplicate]

Question

So I have a flags Enum

public Enum test { test1 = 1, test2 = 2, test3 = 4, etc. }

How can I test that one bit, and only one bit is set?

I've 100% done this before but my mind is not working this am!

spender · Accepted Answer · 2013-10-15 09:02:54Z

13

To check that only a single bit is set in a number, the number must (by definition) be a power of two. As such, you can use the following to test:

int intVal = ((int)myEnumFlags); bool singleBitIsSet = intVal != 0 && (intVal & (intVal-1)) == 0;

My favorite reference for this kind of thing:

http://aggregate.org/MAGIC

edited Oct 15, 2013 at 9:02

answered Oct 15, 2013 at 8:49

spender

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4 Comments

Ahmed KRAIEM Over a year ago

Please note that this won't work when intVal == 0. 0 has no bit set but 0 & -1 == 0

Ahmed KRAIEM Over a year ago

"To check that only a single bit is set in a number, the number must (by definition) be a power of two." Unless it's 0 wich isn't a power of 2 but has not bit set.

spender Over a year ago

@AhmedKRAIEM : you are right. Updated my answer. It might be more efficient to swap the order of the test, depending on which values are more likely.

Cee McSharpface Over a year ago

made an extension using the code from this answer. can now write enumvalue.IsSingleFlag (in addition to enumvalue.HasFlag, which Comes with the framework)

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