CODEWITHSUNDEEP
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Reputation: 2402

enum with value 0x0001?

I have an enum declaration like this:

public enum Filter
{
  a = 0x0001;
  b = 0x0002;
}

What does that mean? They are using this to filter an array.

Upvotes: 7

Views: 16605

Answers (9)

JP Alioto
JP Alioto

Reputation: 45117

Those are literal hexadecimal numbers. Hex is used often times in this situation because it's easier to "see" when used as a bitmask with operations like bitwise and (&) as well as or (|).

Upvotes: 2

Antoine Meltzheim
Antoine Meltzheim

Reputation: 9924

Main reason is :

It is easyer to read hex notation when writing numbers such as : "2 to the power of x" is needed.

To use enum type as bit flag, we need to increment enum values by power of 2 ... 1,2,4,8,16,32,64, etc. To keep it readable, hex notation is used.

Ex : 2^10 is 0x10000 in hex (neat and clean), but it is written 65536 in classical decimal notation ... Same for 0x200 (hex notation) and 512. (2^9)

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500785

It means they're the integer values assigned to those names. Enums are basically just named numbers. You can cast between the underlying type of an enum and the enum value.

For example:

public enum Colour
{
    Red = 1,
    Blue = 2,
    Green = 3
}

Colour green = (Colour) 3;
int three = (int) Colour.Green;

By default an enum's underlying type is int, but you can use any of byte, sbyte, short, ushort, int, uint, long or ulong:

public enum BigEnum : long
{
    BigValue = 0x5000000000 // Couldn't fit this in an int
}

Upvotes: 10

Guffa
Guffa

Reputation: 700362

It's not clear what it is that you find unclear, so let's discuss it all:

The enum values have been given explicit numerical values. Each enum value is always represented as a numerical value for the underlying storage, but if you want to be sure what that numerical value is you have to specify it.

The numbers are written in hexadecimal notation, this is often used when you want the numerical values to contain a single set bit for masking. It's easier to see that the value has only one bit set when it's written as 0x8000 than when it's written as 32768.

In your example it's not as obvious as you have only two values, but for bit filtering each value represents a single bit so that each value is twice as large as the previous:

public enum Filter {
   First = 0x0001,
   Second = 0x0002,
   Third = 0x0004,
   Fourth = 0x0008
}

You can use such an enum to filter out single bits in a value:

If ((num & Filter.First) != 0 && (num & Filter.Third) != 0) {
   Console.WriteLine("First and third bits are set.");
}

Upvotes: 5

Ankur
Ankur

Reputation: 161

Well we can use integers infact we can avoid any as the default nature of enum assigns 0 to its first member and an incremented value to the next available member. Many developers use this to hit two targets with one bow.

  • Complicate the code making it difficult to understand
  • Faster the performance as hex codes are nearer to binary one

my view is if we are still using why we are in fourth generation language just move to binary again

but its quite better technique to play with bits and encryption/decryption process

Upvotes: 0

foobarfuzzbizz
foobarfuzzbizz

Reputation: 58657

It just means that if you do Filter->a, you get 1. Filter->b is 2.

The weird hex notation is just that, notation.

EDIT: Since this is a 'filter' the hex notation makes a little more sense.

By writing 0x1, you specify the following bit pattern:

0000 0001

And 0x2 is:

0000 0010

This makes it clearer on how to use a filter.

So for example, if you wanted to filter out data that has the lower 2 bits set, you could do:

Filter->a | Filter->b

which would correspond to:

0000 0011

The hex notation makes the concept of a filter clearer (for some people). For example, it's relatively easy to figure out the binary of 0x83F0 by looking at it, but much more difficult for 33776 (the same number in base 10).

Upvotes: 9

Brian
Brian

Reputation: 2261

Using Hexidecimal notation like that usually indicates that there may be some bit manipulation. I've used this notation often when dealing with this very thing, for the very reason you asked this question - this notation sort of pops out at you and says "Pay attention to me I'm important!"

Upvotes: 0

Kredns
Kredns

Reputation: 37211

It could mean anything. We need to see more code then that to be able to understand what it's doing.

0x001 is the number 1. Anytime you see the 0x it means the programmer has entered the number in hexadecimal.

Upvotes: 2

DigitalZebra
DigitalZebra

Reputation: 41503

Those look like they are bit masks of some sort. But their actual values are 1 and 2...

You can assign values to enums such as:

enum Example {
    a = 10,
    b = 23,
    c = 0x00FF
}

etc...

Upvotes: 0

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