Convert a string to an enum in C

Question

What s the best way to convert a string to an enumeration value in C   I have an HTML select tag containing the values of an enumeration  When the page is posted  I want to pick up the value  which will be in the form of a string  and convert it to the corresponding enumeration value  In an ideal world  I could do something like this  StatusEnum MyStatus   StatusEnum Parse  quot Active quot     but that isn t a valid code

User · Answer

You have to use Enum Parse to get the object value from Enum  after that you have to change the object value to specific enum value  Casting to enum value can be do by using Convert ChangeType  Please have a look on following code snippet  public T ConvertStringValueToEnum lt T gt  string valueToParse       return Convert ChangeType Enum Parse typeof T   valueToParse  true   typeof T

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If the property name is different from what you want to call it  i e  language differences  you can do like this   MyType cs  using System  using System Runtime Serialization  using Newtonsoft Json  using Newtonsoft Json Converters    JsonConverter typeof StringEnumConverter    public enum MyType        EnumMember Value    person        Person       EnumMember Value    annan deltagare        OtherPerson       EnumMember Value    regel        Rule      EnumExtensions cs  using System  using Newtonsoft Json  using Newtonsoft Json Converters   public static class EnumExtensions       public static TEnum ToEnum lt TEnum gt  this string value  where TEnum   Enum               var jsonString       value ToLower               return JsonConvert DeserializeObject lt TEnum gt  jsonString  new StringEnumConverter                public static bool EqualsTo lt TEnum gt  this string strA  TEnum enumB  where TEnum   Enum               TEnum enumA          try                       enumA   strA ToEnum lt TEnum gt                       catch                       return false                    return enumA Equals enumB             Program cs  public class Program       static public void Main String   args                  var myString    annan deltagare           var myType   myString ToEnum lt MyType gt             var isEqual   myString EqualsTo MyType OtherPerson             Output  true

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For performance this might help       private static Dictionary lt Type  Dictionary lt string  object gt  gt  dicEnum   new Dictionary lt Type  Dictionary lt string  object gt  gt         public static T ToEnum lt T gt  this string value  T defaultValue                var t   typeof T           Dictionary lt string  object gt  dic          if   dicEnum ContainsKey t                         dic   new Dictionary lt string  object gt                 dicEnum Add t  dic               foreach  var en in Enum GetValues t                   dic Add en ToString    en                     else             dic   dicEnum t           if   dic ContainsKey value               return defaultValue          else             return  T dic value

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Super simple code using TryParse   var value    Active    StatusEnum status  if   Enum TryParse lt StatusEnum gt  value  out status       status   StatusEnum Unknown

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Not sure when this was added but on the Enum class there is now a   Parse lt TEnum gt  stringValue   Used like so with example in question   var MyStatus   Enum Parse lt StatusEnum  gt   Active    or ignoring casing by   var MyStatus   Enum Parse lt StatusEnum  gt   active   true   Here is the decompiled methods this uses        NullableContext 0       public static TEnum Parse lt TEnum gt   Nullable 1   string value  where TEnum   struct             return Enum Parse lt TEnum gt  value  false               NullableContext 0       public static TEnum Parse lt TEnum gt   Nullable 1   string value  bool ignoreCase  where TEnum   struct             TEnum result        Enum TryParse lt TEnum gt  value  ignoreCase  true  out result         return result

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public TEnum ToEnum lt TEnum gt  this string value  TEnum defaultValue   if  string IsNullOrEmpty value       return defaultValue   return Enum Parse typeof TEnum   value  true

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lt Extension   gt      Public Function ToEnum Of TEnum  ByVal value As String  ByVal defaultValue As TEnum  As TEnum         If String IsNullOrEmpty value  Then             Return defaultValue         End If          Return  Enum  Parse GetType TEnum   value  True      End Function

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str ToEnum lt EnumType gt    T static ToEnum lt T gt  this string str          return  T  Enum Parse typeof T   str

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object Enum Parse System Type enumType  string value  bool ignoreCase     So if you had an enum named mood it would look like this      enum Mood            Angry        Happy        Sad                     Mood m    Mood  Enum Parse typeof Mood    Happy   true      Console WriteLine  My mood is   0    m ToString

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public static T ParseEnum lt T gt  string value               function declaration         return  T  Enum Parse typeof T   value      Importance imp   EnumUtil ParseEnum lt Importance gt   Active        function call                       A Complete Program                      using System   class Program       enum PetType           None      Cat   1      Dog   2            static void Main                 Possible user input      string value    Dog           Try to convert the string to an enum      PetType pet    PetType Enum Parse typeof PetType   value           See if the conversion succeeded      if  pet    PetType Dog                Console WriteLine  Equals dog                   ------------- Output  Equals dog

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Parses string to TEnum without try catch and without TryParse   method from  NET 4 5       lt summary gt      Parses string to TEnum without try catch and  NET 4 5 TryParse        lt  summary gt  public static bool TryParseToEnum lt TEnum gt  string probablyEnumAsString   out TEnum enumValue   where TEnum   struct       enumValue     TEnum Enum GetValues typeof TEnum   GetValue 0       if  Enum IsDefined typeof TEnum   probablyEnumAsString            return false       enumValue     TEnum  Enum Parse typeof TEnum   probablyEnumAsString        return true

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We couldn t assume perfectly valid input  and went with this variation of  Keith s answer   public static TEnum ParseEnum lt TEnum gt  string value  where TEnum   struct       TEnum tmp       if   Enum TryParse lt TEnum gt  value  true  out tmp                 tmp   new TEnum              return tmp

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BEWARE   enum Example       One   1      Two   2      Three   3     Enum  Try Parse   accepts multiple  comma-separated arguments  and combines them with binary  or     You cannot disable this and in my opinion you almost never want it   var x   Enum Parse  One Two       x is now Three   Even if Three was not defined  x would still get int value 3  That s even worse  Enum Parse   can give you a value that is not even defined for the enum   I would not want to experience the consequences of users  willingly or unwillingly  triggering this behavior   Additionally  as mentioned by others  performance is less than ideal for large enums  namely linear in the number of possible values   I suggest the following       public static bool TryParse lt T gt  string value  out T result          where T   struct               var cacheKey    Enum     typeof T  FullName               Use MemoryCache to retrieve or create amp store a dictionary for this enum  permanently or temporarily              Implementation off-topic           var enumDictionary   CacheHelper GetCacheItem cacheKey  CreateEnumDictionary lt T gt   EnumCacheExpiration            return enumDictionary TryGetValue value Trim    out result              private static Dictionary lt string  T gt  CreateEnumDictionary lt T gt                  return Enum GetValues typeof T                Cast lt T gt                 ToDictionary value   gt  value ToString    value   gt  value  StringComparer OrdinalIgnoreCase

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Enum Parse is your friend   StatusEnum MyStatus    StatusEnum Enum Parse typeof StatusEnum    Active

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Note that the performance of Enum Parse   is awful  because it is implemented via reflection   The same is true of Enum ToString  which goes the other way     If you need to convert strings to Enums in performance-sensitive code  your best bet is to create a Dictionary lt String YourEnum gt  at startup and use that to do your conversions

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You re looking for Enum Parse   SomeEnum enum    SomeEnum Enum Parse typeof SomeEnum    EnumValue

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Use Enum TryParse lt T gt  String  T      NET 4 0    StatusEnum myStatus  Enum TryParse  Active   out myStatus     It can be simplified even further with C  7 0 s parameter type inlining   Enum TryParse  Active   out StatusEnum myStatus

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Try this sample    public static T GetEnum lt T gt  string model                var newModel   GetStringForEnum model            if   Enum IsDefined typeof T   newModel                         return  T Enum Parse typeof T    None   true                      return  T Enum Parse typeof T   newModel Result  true              private static Task lt string gt  GetStringForEnum string model                return Task Run      gt                        Regex rgx   new Regex    a-zA-Z0-9 -                 var nonAlphanumericData   rgx Matches model               if  nonAlphanumericData Count  lt  1                                return model                            foreach  var item in nonAlphanumericData                                model   model Replace  string item                                 return model                      In this sample you can send every string  and set your Enum  If your Enum had data that you wanted  return that as your Enum type

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I like the extension method solution    namespace System       public static class StringExtensions                public static bool TryParseAsEnum lt T gt  this string value  out T output  where T   struct                       T result               var isEnum   Enum TryParse value  out result                output   isEnum   result   default T                return isEnum                      Here below my implementation with tests   using static Microsoft VisualStudio TestTools UnitTesting Assert  using static System Console   private enum Countries               NorthAmerica          Europe          Rusia          Brasil          China          Asia          Australia            TestMethod          public void StringExtensions On TryParseAsEnum                         var countryName    Rusia                Countries country              var isCountry   countryName TryParseAsEnum out country                WriteLine country                IsTrue isCountry               AreEqual Countries Rusia  country                countryName    Don t exist                isCountry   countryName TryParseAsEnum out country                WriteLine country                IsFalse isCountry               AreEqual Countries NorthAmerica  country      the 1rst one in the enumeration

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I used class  strongly-typed version of Enum with parsing and performance improvements   I found it on GitHub  and it should work for  NET 3 5 too  It has some memory overhead since it buffers a dictionary   StatusEnum MyStatus   Enum lt StatusEnum gt  Parse  Active      The blogpost is Enums     Better syntax  improved performance and TryParse in NET 3 5   And code  https   github com damieng DamienGKit blob master CSharp DamienG Library System EnumT cs

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You can use extension methods now   public static T ToEnum lt T gt  this string value  bool ignoreCase   true        return  T  Enum Parse typeof  T   value  ignoreCase       And you can call them by the below code  here  FilterType is an enum type    FilterType filterType   type ToEnum lt FilterType gt

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In  NET Core and  NET Framework  4 0 there is a generic parse method  Enum TryParse  quot Active quot   out StatusEnum myStatus    This also includes C 7 s new inline out variables  so this does the try-parse  conversion to the explicit enum type and initialises populates the myStatus variable  If you have access to C 7 and the latest  NET this is the best way  Original Answer In  NET it s rather ugly  until 4 or above   StatusEnum MyStatus    StatusEnum  Enum Parse typeof StatusEnum    quot Active quot   true    I tend to simplify this with  public static T ParseEnum lt T gt  string value        return  T  Enum Parse typeof T   value  true      Then I can do  StatusEnum MyStatus   EnumUtil ParseEnum lt StatusEnum gt   quot Active quot     One option suggested in the comments is to add an extension  which is simple enough  public static T ToEnum lt T gt  this string value        return  T  Enum Parse typeof T   value  true      StatusEnum MyStatus    quot Active quot  ToEnum lt StatusEnum gt      Finally  you may want to have a default enum to use if the string cannot be parsed  public static T ToEnum lt T gt  this string value  T defaultValue         if  string IsNullOrEmpty value                 return defaultValue             T result      return Enum TryParse lt T gt  value  true  out result    result   defaultValue     Which makes this the call  StatusEnum MyStatus    quot Active quot  ToEnum StatusEnum None    However  I would be careful adding an extension method like this to string as  without namespace control  it will appear on all instances of string whether they hold an enum or not  so 1234 ToString   ToEnum StatusEnum None  would be valid but nonsensical    It s often be best to avoid cluttering Microsoft s core classes with extra methods that only apply in very specific contexts unless your entire development team has a very good understanding of what those extensions do

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You can extend the accepted answer with a default value to avoid exceptions   public static T ParseEnum lt T gt  string value  T defaultValue  where T   struct       try               T enumValue          if   Enum TryParse value  true  out enumValue                         return defaultValue                    return enumValue            catch  Exception                return defaultValue            Then you call it like   StatusEnum MyStatus   EnumUtil ParseEnum  Active   StatusEnum None     If the default value is not an enum the Enum TryParse would fail and throw an exception which is catched   After years of using this function in our code on many places maybe it s good to add the information that this operation costs performance

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I found that here the case with enum values that have EnumMember value was not considered  So here we go   using System Runtime Serialization   public static TEnum ToEnum lt TEnum gt  this string value  TEnum defaultValue  where TEnum   struct       if  string IsNullOrEmpty value                 return defaultValue             TEnum result      var enumType   typeof TEnum       foreach  var enumName in Enum GetNames enumType                 var fieldInfo   enumType GetField enumName           var enumMemberAttribute     EnumMemberAttribute    fieldInfo GetCustomAttributes typeof EnumMemberAttribute   true   FirstOrDefault            if  enumMemberAttribute  Value    value                        return Enum TryParse enumName  true  out result    result   defaultValue                       return Enum TryParse value  true  out result    result   defaultValue      And example of that enum   public enum OracleInstanceStatus       Unknown   -1      Started   1      Mounted   2      Open   3       EnumMember Value    OPEN MIGRATE        OpenMigrate   4

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If you want to use a default value when null or empty  e g  when retrieving from config file and the value does not exist  and throw an exception when the string or number does not match any of the enum values  Beware of caveat in Timo s answer though  https   stackoverflow com a 34267134 2454604        public static T ParseEnum lt T gt  this string s  T defaultValue  bool ignoreCase   false           where T   struct  IComparable  IConvertible  IFormattable  If C   gt  7 3  struct  System Enum                if   s  Length    0     0                        return defaultValue                     var valid   Enum TryParse lt T gt  s  ignoreCase  out T res            if   valid     Enum IsDefined typeof T   res                         throw new InvalidOperationException                      s   is not a valid value of enum   typeof T  FullName                         return res

[c#] Convert a string to an enum in C#

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