How to clear a single bit in C#?

Question

I did it like that: How do you set, clear and toggle a single bit in C?.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1 << x);

That will clear bit x. You must invert the bit string with the bitwise NOT operator (~), then AND it.

It works fine with signed integer types, but doesn't work with unsigned integer (e.g. UInt32). Compiler says that it's impossible to do that kind of operation to unsigned types. How to deal with unsigned numbers to clear one bit then ?

score 2 · Accepted Answer · answered Jul 14 '13 at 09:48

2

It doesn't actually say that. It says "Cannot implicitly convert type 'int' to 'uint'. An explicit conversion exists (are you missing a cast?)"

That's because 1 << x will be of type int.

Try 1u << x.

answered Jul 14 '13 at 09:48

harold

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score 1 · Answer 2 · answered Jul 14 '13 at 09:47

1

UInt32 number = 40;
Int32 x = 5;
number &= ~((UInt32)1 << x);

answered Jul 14 '13 at 09:47

Tarik

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Yes, the shifter has to be signed, the shiftee can be unsigned. And `(UInt32)1` can be written `1U` – H H Jul 14 '13 at 12:39

pascalhein · Answer 3 · 2013-07-14T09:49:36.993

0

You can cast the result, which is a long, back to a uint if you replace the compound operator &= with a normal &:

uint number = /*...*/;
number = (uint)(number & ~(1 << x));

Another way would be to use the unchecked block:

uint number = /*...*/;
unchecked
{
    number &= (uint)~(1 << x);
}

edited Jul 14 '13 at 09:49

answered Jul 14 '13 at 09:40

pascalhein

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No (intermediate) result is `long`. – H H Jul 14 '13 at 12:39
@HenkHolterman: `(number & ~(1 << x)).GetType()` is `System.Int64` – pascalhein Jul 14 '13 at 13:07
To my surprise, yes. But `(number & ~(1U << x)).GetType()` is `System.Int32` – H H Jul 14 '13 at 15:18

How to clear a single bit in C#?

3 Answers3