How to get the Enum Index value in C

Question

In C  enums  internally equates to an integer  Therefore we can treat data types of enum as integer also   How to achieve the same with C

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Use simple casting   int value    int  enum item      Refer to enum  C  Reference

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using System  public class EnumTest        enum Days  Sat 1  Sun  Mon  Tue  Wed  Thu  Fri        static void Main                   int x    int Days Sun          int y    int Days Fri          Console WriteLine  Sun    0    x           Console WriteLine  Fri    0    y

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By default the underlying type of each element in the enum is integer   enum Values      A     B     C     You can also specify custom value for each item   enum Values      A   10     B   11     C   12   int x    int Values A     x will be 10    Note  By default  the first enumerator has the value 0

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One reason that the designers c  might have chosen to NOT have enums auto convert was to prevent accidentally mixing different enum types      e g  this is bad code followed by a good version enum ParkingLevel   GroundLevel  FirstFloor   enum ParkingFacing   North  East  South  West   void Test         var parking   ParkingFacing North     NOT A LEVEL        WHOOPS at least warning in editor compile on calls     WhichLevel parking            BAD  wrong type of index  no warning     var info   ParkinglevelArray   int parking           however you can write this  looks complicated     but avoids using casts every time AND stops miss-use void Test       ParkingLevelManager levels   new ParkingLevelManager         assign info to each level   var parking   ParkingFacing North        Next line wrong mixing type       but great you get warning in editor or at compile time         var info levels parking         and     no cast needed for correct use   var pl   ParkingLevel GroundLevel    var infoCorrect levels pl      class ParkingLevelInfo             class ParkingLevelManager       List lt ParkingLevelInfo gt  m list      public ParkingLevelInfo this ParkingLevel x      get  return m list  int x

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Use a cast   public enum MyEnum   int          A   0      B   1      AB   2      int val    int MyEnum A

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Firstly  there could be two values that you re referring to  Underlying Value If you are asking about the underlying value  which could be any of these types  byte  sbyte  short  ushort  int  uint  long or ulong Then you can simply cast it to it s underlying type  Assuming it s an int  you can do it like this  int eValue    int enumValue   However  also be aware of each items default value  first item is 0  second is 1 and so on  and the fact that each item could have been assigned a new value  which may not necessarily be in any order particular order   Credit to  JohnStock for the poke to clarify   This example assigns each a new value  and show the value returned  public enum MyEnum       MyValue1   34      MyValue2   27     int MyEnum MyValue2    27     True  Index Value The above is generally the most commonly required value  and is what your question detail suggests you need  however each value also has an index value  which you refer to in the title   If you require this then please see other answers below for details

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Another way to convert an Enum-Type to an int   enum E       A   1       index 0        B   2       index 1        C   4       index 2        D   4       index 3  duplicate use of 4       void Main         E e   E C      int index   Array IndexOf Enum GetValues e GetType     e          index is 2      E f    E  Enum GetValues e GetType     GetValue index          f is  E C     More complex but independent from the INT values assigned to the enum values

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In answering this question I define  value  as the value of the enum item  and index as is positional location in the Enum definition  which is sorted by value   The OP s question asks for  index  and various answer have interpreted this as either  index  or  value   by my definitions   Sometimes the index is equal to numerical value  No answer has specifically addressed the case of finding the index  not value  where the Enum is an Enum flag  Enum Flag       none   0          not a flag  thus index  -1     A   1  lt  lt  0       index should be 0     B   1  lt  lt  1       index should be 1      C   1  lt  lt  2       index should be 2      D   1  lt  lt  3       index should be 3      AandB   A   B    index is composite  thus index   -1 indicating undefined     All   -1        index is composite  thus index   -1 indicating undefined    In the case of Flag Enums  the index is simply given by var index    int  Math Log2  int flag      Shows the maths  but is inefficient  However  the above solution is  a  Inefficient as pointed out by  phuclv  Math Log2   is floating point and costly  and  b  Does not address the Flag none case  nor any composite flags - flags that are composed of other flags  eg the  AandB  flag as in my example   DotNetCore If using dot net core we can address both a  and b  above as follows  int setbits   BitOperations PopCount  uint flag     get number of set bits if  setbits    1    Finds ECalFlags none  and all composite flags     return -1      undefined index int index   BitOperations TrailingZeroCount  uint flag     Efficient bit operation  Not DotNetCore The BitOperations only work in dot net core   See  phuclv answer here for some efficient suggestions  https   stackoverflow com a 63582586 6630192   user1027167 answer will not work if composite flags are used  as per my comment on his answer Thankyou to  phuclv for suggestions on improving efficiency

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You can directly cast it   enum MyMonthEnum   January   1  February  March  April  May  June  July  August  September  October  November  December     public static string GetMyMonthName int MonthIndex      MyMonthEnum MonthName    MyMonthEnum MonthIndex    return MonthName ToString        For Example   string MySelectedMonthName GetMyMonthName 8      then MySelectedMonthName value will be August

[c#] How to get the Enum Index value in C#

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