How can I cast int to enum?

Question

How can an int be cast to an enum in C#?

Solution 1

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Solution 2

Just cast it:

MyEnum e = (MyEnum)3;

You can check if it's in range using Enum.IsDefined:

if (Enum.IsDefined(typeof(MyEnum), 3)) { ... }

Solution 3

Alternatively, use an extension method instead of a one-liner:

public static T ToEnum<T>(this string enumString)
{
    return (T) Enum.Parse(typeof (T), enumString);
}

Usage:

Color colorEnum = "Red".ToEnum<Color>();

OR

string color = "Red";
var colorEnum = color.ToEnum<Color>();

Solution 4

I think to get a complete answer, people have to know how enums work internally in .NET.

How stuff works

An enum in .NET is a structure that maps a set of values (fields) to a basic type (the default is int). However, you can actually choose the integral type that your enum maps to:

public enum Foo : short

In this case the enum is mapped to the short data type, which means it will be stored in memory as a short and will behave as a short when you cast and use it.

If you look at it from a IL point of view, a (normal, int) enum looks like this:

.class public auto ansi serializable sealed BarFlag extends System.Enum
{
    .custom instance void System.FlagsAttribute::.ctor()
    .custom instance void ComVisibleAttribute::.ctor(bool) = { bool(true) }

    .field public static literal valuetype BarFlag AllFlags = int32(0x3fff)
    .field public static literal valuetype BarFlag Foo1 = int32(1)
    .field public static literal valuetype BarFlag Foo2 = int32(0x2000)

    // and so on for all flags or enum values

    .field public specialname rtspecialname int32 value__
}

What should get your attention here is that the value__ is stored separately from the enum values. In the case of the enum Foo above, the type of value__ is int16. This basically means that you can store whatever you want in an enum, as long as the types match.

At this point I'd like to point out that System.Enum is a value type, which basically means that BarFlag will take up 4 bytes in memory and Foo will take up 2 -- e.g. the size of the underlying type (it's actually more complicated than that, but hey...).

The answer

So, if you have an integer that you want to map to an enum, the runtime only has to do 2 things: copy the 4 bytes and name it something else (the name of the enum). Copying is implicit because the data is stored as value type - this basically means that if you use unmanaged code, you can simply interchange enums and integers without copying data.

To make it safe, I think it's a best practice to know that the underlying types are the same or implicitly convertible and to ensure the enum values exist (they aren't checked by default!).

To see how this works, try the following code:

public enum MyEnum : int
{
    Foo = 1,
    Bar = 2,
    Mek = 5
}

static void Main(string[] args)
{
    var e1 = (MyEnum)5;
    var e2 = (MyEnum)6;

    Console.WriteLine("{0} {1}", e1, e2);
    Console.ReadLine();
}

Note that casting to e2 also works! From the compiler perspective above this makes sense: the value__ field is simply filled with either 5 or 6 and when Console.WriteLine calls ToString(), the name of e1 is resolved while the name of e2 is not.

If that's not what you intended, use Enum.IsDefined(typeof(MyEnum), 6) to check if the value you are casting maps to a defined enum.

Also note that I'm explicit about the underlying type of the enum, even though the compiler actually checks this. I'm doing this to ensure I don't run into any surprises down the road. To see these surprises in action, you can use the following code (actually I've seen this happen a lot in database code):

public enum MyEnum : short
{
    Mek = 5
}

static void Main(string[] args)
{
    var e1 = (MyEnum)32769; // will not compile, out of bounds for a short

    object o = 5;
    var e2 = (MyEnum)o;     // will throw at runtime, because o is of type int

    Console.WriteLine("{0} {1}", e1, e2);
    Console.ReadLine();
}

Solution 5

Take the following example:

int one = 1;
MyEnum e = (MyEnum)one;

View more solutions

Comments

[dtroy]

Beware you can't use Enum.IsDefined if you use the Flags attribute and the value is a combination of flags for example: Keys.L | Keys.Control

[CodesInChaos]

That's useful when converting from a string. But not when converting from an int.

[Tathagat Verma]

That correct it should be: YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString) OR YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourInt) -- As applicable.

[Shimmy Weitzhandler]

@FlySwat, what if YourEnum is dynamic and will only be known at runtime, and what I want is to convert to Enum?

[Olivier Jacot-Descombes]

@Shimmy. If the enum is only known at runtime, keep it dynamic. Type safety (strong typing) can only be guaranteed by the compiler anyway. You cannot strongly type an object at runtime. The closest you can come to it is by using generics, but the generic type must be known at compile time. T ToEnum<T>(int x) { return (T)x; } but there is no real advantage over casting directly.

[Logan]

Quick question, if you were to go back from YourEnum foo to int anInt type: anInt = (int)foo; would that work?

[Jeppe Stig Nielsen]

@Logan Sure, it works. (If the underlying integer type of the enum is not int, cast to that underlying integer type instead. But it is extremely rare that the underlying type should be something else than simply int.)

[jropella]

Be aware that Enum.Parse will NOT work if your code is obfuscated. At run time after obfuscation the string is compared to the enum names, and at this point the names of the enums aren't what you would expect them to be. Your parse will fail where they succeeded before as a result.

[BrainSlugs83]

For processing user input, it's probably a good idea to call the overload of Enum.Parse that is allows you to specify that the comparison NOT be case sensitive (i.e. a user typing "red" (lowercase) would crash the above code without this change.)

[JoeCool]

BEWARE If you use the "from a string" syntax above and pass in an invalid string that is a number (e.g. "2342342" -- assuming that's not a value of your enum), it will actually allow that without throwing an error! Your enum will have that value (2342342) even though it's not a valid choice in the enum itself.

[Justin T Conroy]

I think this answer is a bit dated now. For string, you should really be using var result = Enum.TryParse(yourString, out yourEnum) nowadays (and checking the result to determine if the conversion failed).

[adrian]

Regarding Enum.IsDefined, be aware that it can be dangerous: msdn.microsoft.com/en-us/library/ms229025(VS.90).aspx

[jackvsworld]

@JustinTConroy I don't know if I agree with that. In my programs, if the conversion fails it's often a non-recoverable error, so I want the exception to be thrown.

[Justin T Conroy]

The Parse function presents a classic example of a vexing exception. That is, an exception that is thrown in a completely non-exceptional circumstance, usually due to an unfortunate design decision. The developers of C# recognized this unfortunate design and later added TryParse to deal with this. TryParse returns a boolean that indicates if the parse succeeded or failed, so you should use that boolean instead of an exception handler. See Eric Lippert's blog post about vexing exceptions for more information.

[Erik Schierboom]

It is also possible to have Enum.Parse be case-insensitive by adding a true parameter value to the call: YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString, true);

[Pap]

I prefer this definition: "Returns an indication whether a constant with a specified value exists in a specified enumeration" from MSDN

[Pap]

...Because your definition can be misleading, because you are saying: "...check if it's in range..." which implies within a range of numbers with starting and ending limits...

[Paul Richards]

enums superseded the use of integer constants like this since they provide more type safety

[Ted]

Paul, this is a method of collecting together related int constants (e.g. Database id constants) so they can be used directly without having to cast them to int every time they're used. Their type is integer, not for example, DatabaseIdsEnum.

[Thierry]

There is at least one situation that I have found in which enum type safety can be unintentionally bypassed.

[Santhos]

Is it possible that the conversion from int works even if the int value is not present in the enum? I just tried it in .net 3.5 and it seems to work which is quite confusing.

[Colin]

Enum.ToObject was what I was looking for. This is exactly what you need when working with enums dynamically and you have a type that you know is an enum but can't prove it to the compiler, which won't allow you to cast from an int value to an arbitrary type.

[Thaoden]

@Santhos Yes, there is Enum.IsDefined() to check if the value you want to convert exists in your enum.

[BJury]

The question specifically asks about integers.

[BJury]

Handy, but the question specifically asks about ints.

[Aidiakapi]

@JustinTConroy Except that it's not. When you call Parse, you trust the input value to be correct, and when it isn't, it's a bug in the code (and there's an exception as there should be). If you're dealing with user input, you should always call TryParse, because invalid input isn't exceptional. The article you linked mentions this in "the 99% use case for this method is transforming strings input by the user", that's the bug, the method isn't designed to handle user input, TryParse is.

[Rolan]

I realize this is an old post, but how do you gain this level of knowledge in c#? Is this from reading through the C# specification?

[atlaste]

@Rolan I sometimes wish more people would ask that. :-) To be honest I don't really know; I try to understand how things work and get information wherever I can get it. I did read the C# standard, but I also regularly decompile code with Reflector (I even look at the x86 assembler code a lot) and do tons of little experiments. Also, knowing about other languages helps in this case; I've been doing CS for about 30 years now, and at some point certain things become 'logical' - f.ex. an enum should integral types, because otherwise interop will break (or your performance will go down the drain).

[atlaste]

I believe the key to doing software engineering properly is knowing how stuff works. For me that means that if you write a piece of code, you know how it roughly translates to f.ex. processor operations and memory fetches / writes. If you ask how to get to that level, I'd suggest building a ton of small test cases, making them tougher as you go, try to predict the outcome every time, and test them afterwards (incl. decompilation, etc). After figuring out all the details and all the characteristics, you can check if you got it right in the (dull) standard. At least, that would be my approach.

[orion elenzil]

this is good. i was surprised there's not an exception when casting an invalid value to an int-backed enum.

[JeremyWeir]

Will Yu please edit your answer to let everyone know Enum.TryParse will work on a string of the value or name of the enum (I couldn't resist)

[gravidThoughts]

Fantastic answer, thanks! In your last code sample, it throws an exception at runtime because o is an object. You can cast an int variable to a short as long as it falls within the short range.

[atlaste]

@gravidThoughts Thanks. Actually it's an unboxing operation, so it won't do any implicit conversions like the ones you describe. Casting is sometimes confusing in C# if you don't know the details... Anyhow, because int != short, it will throw (unboxing fails). If you do object o = (short)5;, it will work, because then the types will match. It's not about the range, it's really about the type.

[TruthOf42]

this also works if the string is an integer, e.g. "2"

[Justin]

This will throw an exception if enumString is null (had a similar issue yesterday). Consider using TryParse instead of Parse. TryParse will also check if T is an Enum Type

[Don Cheadle]

This actually is not so different than the top-rated answer. That answer also discusses using Enum.IsDefined after you've casted the string to the Enum type. So even if the string was casted without error, Enum.IsDefined will still catch it

[daniloquio]

Note that an Enum's value is int by default, but that can be changed which may make the cast dangerous. Check @atlastes's answer.

[crenshaw-dev]

@adrian can you provide a succinct example of a dangerous scenario? Having trouble wrapping my head around that doc.

[Scott]

This can now be improved with C# 7.3 by constraining to Enum instead of struct, meaning we don't have to rely on the runtime check!

[adrian]

@mac9416 I've tried to give a succinct example at gist.github.com/alowdon/f7354cda97bac70b44e1c04bc0991bcc - basically by using IsDefined to check input values, you leave yourself vulnerable to people adding new enum values later which would pass an IsDefined check (since the new value exists in the new code), but which might not work with the original code you wrote. It's therefore safer to explicitly specify the enum values that your code is able to handle.

[Mr Anderson]

This type of extension method on System.String seems like namespace pollution

[derHugo]

But enums also make sure the values are all unique, something this approach is also lacking

[Jimi]

In latest C#/.NET you can use E instead of T so you are sure that the method gets called on an Enum class

[MikeBeaton]

This is a nice answer. It's a shame it's so far down the page at the moment!

[qwerty]

If the cast worked, you wouldn't be able to store it as an int.

[Inam Abbas]

Please try to understand int to Enum I think is above answer to help you.

[Ε Г И І И О]

You return default(T) when it's not defined. How is that helping to identify the undefined ones?

[NDUF]

this is actually much better because if the int value is not a defined entry in the enum, you can use a else statement to set enumString to a default value. Thanks

[belka]

works in case of a string not an int for example

[Shah Zain]

Added case for int.