class Program
{
static void Main(string[] args)
{
String value = "Two";
Type enumType = typeof(Numbers);
Numbers number = (Numbers)Enum.Parse(enumType, value);
Console.WriteLine(Enum.Parse(enumType, value));
}
public enum Numbers : int
{
One,
Two,
Three,
Four,
FirstValue = 1
}
}
This is a simplified version of an enum I use in an application. The reason to why some of the enum names doesn't have a value is because I do Enum.Parse with their names as argument, while the ones with a value is parsed from an int.
If you would step through the code above and investigate the 'number' variable, you would see that it in fact is 'Two', but the output in console is 'FirstValue'. At this point I can't see why, do you?
Okay, the solution is simple - just give the valueless enums a value. But I'm still curious.
I suspect that both FirstValue and Two have an internal value of 1, so the system doesn't know which string to output.
public enum Numbers : int
{
One, // defaults to 0
Two, // defaults to 1
Three, // defaults to 2
Four, // defaults to 3
FirstValue = 1 // forced to 1
}
There is a unique integer value for every enum value, but there is not a unique enum value for every integer value.
When you parse "two", it gets stored internally as the integer 1. Then when you try and convert it back to a string, depending on the technique used to lookup that name, you could get either "Two" or "FirstValue". As you stated, the solution is to give every enum value a defined integer value.
Here is an interesting twist to your problem, try the following Enum...
public enum Numbers : int
{
One,
Two,
Four,
FirstValue = 1
}
The console.WriteLine(...) will now print "Two"!
Both Two and FirstValue represent the same number 1 but the actual value seen depends on how the number was converted to its string representation and vice-versa.
The Enum class uses reflection to get the names of the numbers and then stores them in arrays but it sorts the the whole thing before it does so. Then Enum.ToString() does a binary search on the sorted values to get the string representation. Due to the way this is done you may get a different result depending on the number of elements you have in the enumeration!
Now as for the value "seen" in VS I suspect the debugger visualizer for enums uses an algorithm of its own which corrects(?) this bug.
Related
Assume I have this enum defined, where several members have the same underlying value:
enum Number
{
One = 1,
Eins = 1,
Uno = 1
}
According to MSDN documentation:
If multiple enumeration members have the same underlying value and you attempt to retrieve the string representation of an enumeration member's name based on its underlying value, your code should not make any assumptions about which name the method will return.
So for example,
var number = Number.One;
Console.WriteLine(number);
gives me the following output:
Eins
Printing all enum members,
Console.WriteLine($"{Number.One} {Number.Eins} {Number.Uno}");
yields the following output:
Eins Eins Eins
However, taking the nameof of each member,
Console.WriteLine($"{nameof(Number.One)} {nameof(Number.Eins)} {nameof(Number.Uno)}");
gives the following result:
One Eins Uno
So apparently the enum members are separable. Can I take advantage of this separation, i.e. is there any way I can assign a specific Number member to a variable and consistently have that same member returned whenever the variable is accessed?
So apparently the enum members are separable
Well, that's not entirely true... They are only separable at compile time.
You see, nameof is actually an expression evaluated at compile time. It is a constant expression. This can be proved by assigning a nameof expression to a const:
const string a = nameof(Number.One);
It compiles.
Trying to get the string representation of a enum value using string interpolation on the other hand, is evaluated at runtime, so this does not compile:
const string a = $"{Number.One}";
At runtime, the enum cases are not separable, so the answer to:
is there any way I can assign a specific Number member to a variable and consistently have that same member returned whenever the variable is accessed?
is "no".
The only possibility I see to always return an expected enum name is to create a 2nd enum next to your first of the underlying type and with the same values but limit the members to those that you expect (and make sure there are no shared values). Then you can cast from one to the other and use the new enum in your refactored code that relies on specific/expected members.
SomeMethod
Console.WriteLine("{0:G}", (KnownNumber)Number.Eins); // > One
Console.WriteLine("{0:G}", (KnownNumber)Number.Uno); // > One
Console.WriteLine("{0:G}", (KnownNumber)Number.One); // > One
Enums.cs
public enum Number
{
One = 1,
Eins = 1,
Uno = 1
}
public enum KnownNumber
{
One = 1,
Two = 2,
Three = 3
}
Fiddle
I wrote something that should get it work
public static class NumberExtension
{
private static Dictionary<int, string> pointers = new Dictionary<int, string>();
public static unsafe void SetValue(this Number source, string value)
{
if (pointers.ContainsKey((int)&source))
pointers[(int)&source] = value;
else
pointers.Add((int)&source, value);
}
public static unsafe string GetValue(this Number source)
{
if (pointers.ContainsKey((int)&source))
return pointers[(int)&source];
return source.ToString();
}
}
And to use:
Number num = default(Number);
num.SetValue(nameof(Number.Uno));
Console.WriteLine(num.GetValue());
However, it looks like a kind of 'hack' and I do NOT recommend it. It would be better if you look for a better solution.
I've got a enum type defined in my C# code that corresponds to all possible values for the NetConnectionStatus field in Win32_NetworkAdapter WMI table, as documented here.
The documentation shows that the integers 0 through 12 each have a unique status name, but then all integers between 13 and 65,535 are lumped into one bucket called "Other." So here's my code:
[Serializable]
public enum NetConnectionStatus
{
Disconnected = 0,
Connecting = 1,
Connected = 2,
Disconnecting = 3,
HardwareNotPresent = 4,
HardwareDisabled = 5,
HardwareMalfunction = 6,
MediaDisconnected = 7,
Authenticating = 8,
AuthenticationSucceeded = 9,
AuthenticationFailed = 10,
InvalidAddress = 11,
CredentialsRequired = 12,
Other
}
This works fine for the values that are not Other. For instance, I can do this:
var result = (NetConnectionStatus) 2;
Assert.AreEqual(NetConnectionStatus.Connected, result);
But for anything in that higher numeric range, it doesn't work so great. I would like it if I could do this:
var result = (NetConnectionStatus) 20;
Assert.AreEqual(NetConnectionStatus.Other, result);
But right now that result variable gets assigned the literal value 20 instead of Other. Is there some out-of-the-box way of accomplishing this, something akin to Parse() but for integers instead of strings, or perhaps some special attribute I'm unaware of? I would prefer to not write my own wrapper method for this if there is already a good way to accomplish this.
If you have a string value, then the closest thing I can think of is to use Enum.TryParse:
NetConnectionStatus result;
if (Enum.TryParse(stringValue, out result) == false)
result = NetConnectionStatus.Other;
For an integer value that you're casting, you can use:
result = (NetConnectionStatus)integerValue;
if (Enum.GetValues(typeof(NetConnectionStatus)).Contains(result) == false)
result = NetConnectionStatus.Other;
Not really ideal, but in C# enums aren't much more than fancy names for integral values, so it's valid to stuff an integer value not in the defined values of the enums into a value of that enum type.
This solution will handle negative numbers, or cases where you have gaps in your enum values more elegantly than doing numerical comparisons.
it would be nice but no. How about
var result = (NetConnectionStatus) 20;
Assert.IsTrue(result >= (int)NetConnectionStatus.Other);
.NET does not such thing as a "any other" enumeration value bucket. Technically, enumeration (enum) is a pretty set of named constants of some underlying type (which is one of following: sbyte, short, int, long and their unsigned counterparts). You can cast an enum value to/from a corresponding type without any losses, as in this example:
enum TestEnum:int // Explicitly stating a type.
{
OnlyElement=0
}
class Program
{
static void Main(string[] args)
{
// Console.WriteLine implicitly calls ToString of the TestEnum.OnlyElement.
Console.WriteLine("OnlyElement == {0}", TestEnum.OnlyElement);
//TestEnum.OnlyElement equals to 0, as demonstrated by this casting:
Console.WriteLine("(int)OnlyElement == {0}", (int)TestEnum.OnlyElement);
//We can do it in reverse...
Console.WriteLine("(TestEnum)0 == ",(TestEnum)0);
// But what happens when we try to cast a value, which is not
// representable by any of enum's named constants,
// into value of enum in question? No exception is thrown
// whatsoever: enum variable simply holds that value, and,
// having no named constant to associate it with, simply returns
// that value when attempting to "ToString"ify it:
Console.WriteLine("(TestEnum)5 == {0}", (TestEnum)5); //prints "(TestEnum)5 == 5".
Console.ReadKey();
}
}
I'd like to repeat it again, enum in .NET is simply a value of the underlying type with some nice decorations like overriden ToString method and flags checking (look here or here if you want to know more about flags). You cannot have an integer with only 14 values like "0..12 and everything else", and so you cannot have such enum. In your example, NetConnectionStatus.Other simply receives single literal value (I assume it would most probably be '13', as the next available positive value of underlying type - however it actually depends on the compiler) as any other enumeration constant would do if not specified explicitly - and, obviously, it does not become a bucket.
However, there are options to achieve simple equation checks for integers/bytes/shorts/longs - and enums alike. Consider this extension method:
static bool IsOther(this NetConnectionStatus A)
{
return (A < (NetConnectionStatus)0) || (A > (NetConnectionStatus)12);
}
Now you can have a simple assertion like this:
var result = (NetConnectionStatus)10;
Trace.Assert(result.IsOther()); //No assertion is triggered; result is NetConnectionStatus.AuthenticationFailed
and
var result = (NetConnectionStatus)20;
Trace.Assert(result.IsOther()); //Assertion failed; result is undefined!
(Of course you can replace IsOther method with IsNotOther, overload it and pretty much anything else you could do with a method.)
Now there is one more thing. Enum class itself contains a method called IsDefined, which allows you to avoid checks for specific enum's value boundaries (<0, >12), therefore preventing unwanted bugs in case enum values would ever be added/removed, at the small performance cost of unboxing and checking each value in enum for a match (I'm not sure how this works under the hood though, I hope these checks are optimized). So your method would look like this:
static bool IsOther(NetConnectionStatus A)
{
return !Enum.IsDefined(typeof(NetConnectionStatus), A);
}
(However, concluding from enum's name, it seems like you want to make a network application/server, and for these performance might be of very great importance - but most probably I'm just being paranoid and this will not be your application's bottleneck. Stability is much more of concern, and, unless you experience real troubles with performance, it is considered to be much better practice to enable as much stability&safety&portability as possible. Enum.IsDefined is much more understandable, portable and stable than the explicit boundaries checking.)
Hope that helps!
Thanks everyone for the replies. As confirmed by all of you, there is indeed no way to do this out-of-the-box. For the benefit of others I thought I'd post the (custom) code I ended up writing. I wrote an extension method that utilizes a custom attribute on the enum value that I called [CatchAll].
public class CatchAll : Attribute { }
public static class EnumExtensions
{
public static T ToEnum<T, U>(this U value) where T : struct, IConvertible where U : struct, IComparable, IConvertible, IFormattable, IComparable<U>, IEquatable<U>
{
var result = (T)Enum.ToObject(typeof(T), value);
var values = Enum.GetValues(typeof(T)).Cast<T>().ToList();
if (!values.Contains(result))
{
foreach (var enumVal in from enumVal in values
let info = typeof(T).GetField(enumVal.ToString())
let attrs = info.GetCustomAttributes(typeof(CatchAll), false)
where attrs.Length == 1
select enumVal)
{
result = enumVal;
break;
}
}
return result;
}
}
So then I just have to apply that [CatchAll] attribute to the Other value in the enum definition. Then I can do things like this:
int value = 13;
var result = value.ToEnum<NetConnectionStatus, int>();
Assert.AreEqual(NetConnectionStatus.Other, result);
And this:
ushort value = 20;
result = value.ToEnum<NetConnectionStatus, ushort>();
Assert.AreEqual(NetConnectionStatus.Other, result);
What is main use of Enumeration in c#?
Edited:-
suppose I want to compare the string variable with the any enumeration item then how i can do this in c# ?
The definition in MSDN is a good place to start.
An enumeration type (also named an
enumeration or an enum) provides an
efficient way to define a set of named
integral constants that may be
assigned to a variable.
The main benefit of this is that constants can be referred to in a consistent, expressive and type safe way.
Take for example this very simple Employee class with a constructor:
You could do it like this:
public class Employee
{
private string _sex;
public Employee(string sex)
{
_sex = sex;
}
}
But now you are relying upon users to enter just the right value for that string.
Using enums, you can instead have:
public enum Sex
{
Male = 10,
Female = 20
}
public class Employee
{
private Sex _sex;
public Employee(Sex sex)
{
_sex = sex;
}
}
This suddenly allows consumers of the Employee class to use it much more easily:
Employee employee = new Employee("Male");
Becomes:
Employee employee = new Employee(Sex.Male);
Often you find you have something - data, a classification, whatever - which is best expressed as one of several discrete states which can be represented with integers. The classic example is months of the year. We would like the months of the year to be representable as both strings ("August 19, 2010") and as numbers ("8/19/2010"). Enum provides a concise way to assign names to a bunch of integers, so we can use simple loops through integers to move through months.
Enums are strongly typed constants. Enumerations are special sets of named values which all maps to a set of numbers, usually integers. They come in handy when you wish to be able to choose between a set of constant values, and with each possible value relating to a number, they can be used in a wide range of situations. As you will see in our example, enumerations are defined above classes, inside our namespace. This means we can use enumerations from all classes within the same namespace.
using System;
namespace ConsoleApplication1
{
public enum Days { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday }
class Program
{
static void Main(string[] args)
{
Days day = Days.Monday;
Console.WriteLine((int)day);
Console.ReadLine();
}
}
}
Enumeration (Enum) is a variable type. We can find this variable type in C, C# and many other languages.
Basic Idea for Enum is that if we have a group of variable of integer type (by default) then instead of using too much int values just use a Enum. It is efficient way. Let suppose you want to write rainbow colours then you may write like this:
const int Red = 1;
const int Orange = 2;
const int Yellow = 3;
const int Green = 4;
const int Blue = 5;
const int Indigo = 6;
const int Violet = 7;
here you can see that too many int declarations. If you or your program by mistake change the value of any integer varialbe i.e. Violet = 115 instead of 7 then it will very hard to debug.
So, here comes Enum. You can define Enum for any group of variables type integers. For Enum you may write your code like this:
enum rainBowColors
{
red=1,
orange=2,
yellow=3,
green,
blue=8,
indigo=8,
violet=16)
};
rainBowColors is a type and only other variables of the same type can be assigned to this. In C#/C++ you need to type casting while in C you do not to type cast.
Now, if you want to declare a variable of type rainBowColors then in C
enum rainBowColors variableOne = red;
And in C# / C++ you can do this as:
rainBowColors variableOne = red;
There are two meanings of enumeration in C#.
An enumeration (noun) is a set of named values. Example:
public enum Result {
True,
False,
FileNotFound
}
Enumeration (noun form of the verb enumerate) is when you step through the items in a collection.
The IEnumerable<T> interface is used by classes that provide the ability to be enumerated. An array is a simple example of such a class. Another example is how LINQ uses it to return results as enumerable collections.
Edit:
If you want to compare a string to an enum value, you either have to parse the string to the enum type:
if ((Result)Enum.Parse(typeof(Result), theString) == Result.True) ...
or convert the enum value to a string:
if (theString == Result.True.ToString()) ...
(Be careful how you compare the values, depending on whether you want a case sensetive match or not.)
If you want to enumerate a collection and look for a string, you can use the foreach command:
foreach (string s in theCollection) {
if (s == theString) {
// found
}
}
Another advantage of using Enum is that in case of any of the integer value needs to be changed, we need to change only Enum definition and we can avoid changing code all over the place.
An enumeration type (also named an enumeration or an enum) provides an efficient way to define a set of named integral constants that may be assigned to a variable.
http://msdn.microsoft.com/en-us/library/cc138362.aspx
Enumeration (ENUM)
An enum is a value type with a set of related named constants often referred to as an enumerator list. The enum keyword is used to declare an enumeration. It is a primitive data type, which is user defined.
Enums type can be integer (float, int, byte, double etc.). But if you used beside int it has to be cast.
enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
enum Months : byte { Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec };
Lets Take an Example we are taking normal constant in a class like
int a=10;
by mistakely we assign new value to that variable in that same class like
a=20;
then we will get wrong data when we want access them.
enum provide secure way of accessing constant.
Also if we have many feild constant in a class we had to memorize them if we want to use them in a class.
but enum contains group of related name constant, if we want to access the constant then only we had to memorize enum name.
Enumerations in my experience have worked in very specific cases and should be used when you absolutely need to maintain this in your application. Problems come into play with Enums when you are working with multiple developers and some new developer comes on to a project and can adds a enum to the application no errors everything builds but then you have another full stack developer that maintains this same list in a lookup table in a different order. Kaboom!!!!
Burned way to many times with that one even if not intentional. Rule of thumb don't maintain a list of enums in a app over 5 or 6 items. If higher you might as well store them in a lookup table in the DB of your choice.
considering the following enum:
public enum LeadStatus
{
Cold = 1,
Warm = 2,
Hot = 3,
Quote = 5,
Convert = 6
}
How can I convert the integer value back to string when I pull the value from a database. I've tried:
DomainModel.LeadStatus status = (DomainModel.LeadStatus)Model.Status;
but all I seem to get is "status = 0"
What you are looking for is Enum.Parse.
"Converts the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object."
Here is the MSDN page: http://msdn.microsoft.com/en-us/library/essfb559.aspx
Example:
enum Colour
{
Red,
Green,
Blue
}
// ...
Colour c = (Colour) Enum.Parse(typeof(Colour), "Red", true);
Courtesy of http://blogs.msdn.com/tims/archive/2004/04/02/106310.aspx
Between Enum.Parse and Enum.ToString, you should be able to do everything you need.
Given "Model.Status" is the integer from the database, it can be restored to the Enum string value with:
string status = Enum.GetName(typeof(DomainModel.LeadStatus), Model.Status);
Just use ToString() on the enum object
An enumeration in C# is used to provide names for some known values but ANY integer value is permissible in that enumeration, whether it has a named equivalent or not.
In your example, you have not named a zero value, but your status variable initialises to zero. I suspect that it has not changed from this initial value at the point you read it. Therefore, it's string representation is also 0 and you will parse out zero when you parse it.
If I have an enum that's marked with [Flags], is there a way in .NET to test a value of this type to see if it only contains a single value? I can get the result I want using bit-counting, but I'd rather use built-in functions if possible.
When looping through the enum values dynamically, Enum.GetValues() returns the combination flags as well. Calling that function on the enum in the following example returns 4 values. However, I don't want the value combinations included in the inner algorithm. Testing individual enum values for equality is out, since the enum could potentially contain many values, and it also requires extra maintenance when the values in the enum change.
[Flags]
enum MyEnum
{
One = 1,
Two = 2,
Four = 4,
Seven = One | Two | Four,
}
void MyFunction()
{
foreach (MyEnum enumValue in Enum.GetValues(typeof(MyEnum)))
{
if (!_HasSingleValue(enumValue)) continue;
// Guaranteed that enumValue is either One, Two, or Four
}
}
private bool _HasSingleValue(MyEnum value)
{
// ???
}
Related: StackOverflow: Enum.IsDefined on combined flags
You can cast it to int and use the techniques from Bit Twiddling Hacks to check if it's a power of two.
int v = (int)enumValue;
return v != 0 && (v & (v - 1)) == 0;
You can use a combination of IsDefined and checking for powers of 2.
You could you Enum.GetValues and count only those items that are a power of 2 (evenly divisible by 2 with no remainder).