What does "<<" stand for in C#?

Question

What does << do in this piece of code?

[Serializable]
[Flags]
public enum SiteRoles
{
    User = 1 << 0,
    Admin = 1 << 1,
    Helpdesk = 1 << 2
}

http://msdn.microsoft.com/en-us/library/6a71f45d%28VS.71%29.aspx — UpTheCreek, Jan 26 '10 at 09:10
and here: http://stackoverflow.com/questions/2134204/multiple-ways-to-define-c-enums-with-flags-attribute/ — Sergey Teplyakov, Jan 26 '10 at 09:12

score 8 · Answer 1 · answered Jan 26 '10 at 09:12

8

It means bitshift left, so:

int i = 1 << 2;

// 0000 0001 (1)
// shifted left twice
// 0000 0100 (4)

A left bitshift is analogous to multiplying by two, and a right bitshift acts as a divide by two.

Bitshifts are useful because they convey semantics better when working with bitmasks and they are (on x86 at least) faster than multiplication

answered Jan 26 '10 at 09:12

+1, for the commented example! – KMån Jan 26 '10 at 10:28
Shouldn't the decision whether to shift, multiply or add be left to the JITter? – Joey Dec 22 '11 at 10:18

score 7 · Accepted Answer · answered Jan 26 '10 at 09:08

7

answered Jan 26 '10 at 09:08

unwind

score 5 · Answer 3 · answered Jan 26 '10 at 09:08

5

Bitshifting Just like in C++

answered Jan 26 '10 at 09:08

RvdK

I think the confusion stems from `std::ostream` ... – Travis Gockel Jan 26 '10 at 09:09

score 1 · Answer 4 · answered Jan 26 '10 at 09:10

1

answered Jan 26 '10 at 09:10

AutomatedTester

score 1 · Answer 5 · edited Jul 16 '14 at 18:50

1

It is a Bitwise shift.

Admin = 1 << 1 means one's binary value move to left one bit.

The result is

Admin = 2

edited Jul 16 '14 at 18:50

Code Maverick

answered Jan 26 '10 at 09:13

carl

5 Answers5