Convert objective-c typedef to its string equivalent

Question

Assuming that I have a typedef declared in my  h file as such   typedef enum     JSON    XML    Atom    RSS   FormatType    I would like to build a function that converts the numeric value of the typedef to a string   For example  if the message  self toString JSON  was sent  it would return  JSON    The function would look something like this   - NSString    toString  FormatType formatType       need help here   return         Incidentally  if I try this syntax    self toString FormatType JSON     to pass the typedef value to the method  I get an error   What am I missing

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I combined several approaches here  I like the idea of the preprocessor and the indexed list   There s no extra dynamic allocation  and because of the inlining the compiler might be able to optimize the lookup   typedef NS ENUM NSUInteger  FormatType    FormatTypeJSON   0  FormatTypeXML  FormatTypeAtom  FormatTypeRSS  FormatTypeCount     NS INLINE NSString  FormatTypeToString FormatType t      if  t  gt   FormatTypeCount      return nil    define FormatTypeMapping value   value      value    NSString  table FormatTypeCount     FormatTypeMapping FormatTypeJSON                                         FormatTypeMapping FormatTypeXML                                         FormatTypeMapping FormatTypeAtom                                         FormatTypeMapping FormatTypeRSS      undef FormatTypeMapping    return table t

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the following provides a solution such that to add a new enum requires only a one-line edit  similar work to adding a single line in an enum    list     ------------------------------------------------------------------------------    enum to string example  define FOR EACH GENDER tbd            tbd GENDER MALE            tbd GENDER FEMALE            tbd GENDER INTERSEX      define ONE GENDER ENUM name  name  enum       FOR EACH GENDER ONE GENDER ENUM      MAX GENDER      define ONE GENDER name   name  static const char  enumGENDER TO STRING            FOR EACH GENDER ONE GENDER         access string name with enumGENDER TO STRING value     or  to be safe converting from a untrustworthy caller static const char  enumGenderToString unsigned int value        if  value  lt  MAX GENDER                return enumGENDER TO STRING value             return NULL     static void printAllGenders void        for  int ii   0   ii  lt  MAX GENDER   ii                  printf   d  gender  s n   ii  enumGENDER TO STRING ii               ------------------------------------------------------------------------------    you can assign an arbitrary value and or information to each enum   define FOR EACH PERSON tbd            tbd 2  PERSON FRED       Fred        Weasley   GENDER MALE    12            tbd 4  PERSON GEORGE     George      Weasley   GENDER MALE    12            tbd 6  PERSON HARRY      Harry       Potter    GENDER MALE    10            tbd 8  PERSON HERMIONE   Hermione    Granger   GENDER FEMALE  10      define ONE PERSON ENUM value  ename  first  last  gender  age  ename   value  enum       FOR EACH PERSON ONE PERSON ENUM      typedef struct PersonInfoRec       int value      const char  ename      const char  first      const char  last      int gender      int age    PersonInfo    define ONE PERSON INFO value  ename  first  last  gender  age                           ename   ename  first  last  gender  age    static const PersonInfo personInfo            FOR EACH PERSON ONE PERSON INFO        0  NULL  NULL  NULL  0  0         note  if the enum values are not sequential  you need another way to lookup    the information besides personInfo ENUM NAME   static void printAllPersons void        for  int ii   0      ii                  const PersonInfo  pPI    amp personInfo ii           if   pPI- gt ename                        break                    printf   d  enum  -15s   8s  -8s  13s  2d n               pPI- gt value  pPI- gt ename  pPI- gt first  pPI- gt last              enumGenderToString pPI- gt gender   pPI- gt age

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This is really a C question  not specific to Objective-C  which is a superset of the C language   Enums in C are represented as integers  So you need to write a function that returns a string given an enum value  There are many ways to do this  An array of strings such that the enum value can be used as an index into the array or a map structure  e g  an NSDictionary  that maps an enum value to a string work  but I find that these approaches are not as clear as a function that makes the conversion explicit  and the array approach  although the classic C way is dangerous if your enum values are not continguous from 0   Something like this would work   -  NSString  formatTypeToString  FormatType formatType       NSString  result   nil       switch formatType            case JSON              result     JSON               break          case XML              result     XML               break          case Atom              result     Atom               break          case RSS              result     RSS               break          default               NSException raise NSGenericException format   Unexpected FormatType                return result      Your related question about the correct syntax for an enum value is that you use just the value  e g  JSON   not the FormatType JSON sytax  FormatType is a type and the enum values  e g  JSON  XML  etc   are values that you can assign to that type

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Improved  yar1vn answer by dropping string dependency    define VariableName arg       arg   typedef NS ENUM NSUInteger  UserType        UserTypeParent   0      UserTypeStudent   1      UserTypeTutor   2      UserTypeUnknown   NSUIntegerMax        property  nonatomic  UserType type      NSDictionary   typeDisplayNames       return     UserTypeParent    VariableName UserTypeParent                  UserTypeStudent    VariableName UserTypeStudent                  UserTypeTutor    VariableName UserTypeTutor                  UserTypeUnknown    VariableName UserTypeUnknown       -  NSString   typeDisplayName       return   self class  typeDisplayNames    self type        Thus when you ll change enum entry name corresponding string will be changed  Useful in case if you are not going to show this string to user

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Many answers all fairly good   If you are after a generic  Objective C solution that uses some macros     Key feature is it uses the enum as an index into a static array of NSString constants  the array itself is wrapped into a function to make it more like the suite of NSStringFromXXX functions prevalent in the Apple APIs   you will need to  import  NSStringFromEnum h  found here http   pastebin com u83RR3Vk   EDIT  also needs  import  SW Variadic h  found here http   pastebin com UEqTzYLf  Example 1   completely define a NEW enum typedef  with string converters   in myfile h      import  NSStringFromEnum h     define define Dispatch chain cmd enum    enum chain done  0    enum chain entry    enum chain bg    enum chain mt    enum chain alt    enum chain for c    enum chain while    enum chain continue for    enum chain continue while    enum chain break for    enum chain break while    enum chain previous    enum chain if    enum chain else     interface NSString Enum DefinitionAndConverters Dispatch chain cmd      in myfile m       import  myfile h    implementation NSString Enum Converters Dispatch chain cmd      to use     NSString  NSStringFromEnumDispatch chain cmd enum Dispatch chain cmd value     NSStringFromEnumDispatch chain cmd chain for c  returns   chain for c     enum Dispatch chain cmd enumDispatch chain cmdFromNSString NSString  value     enumDispatch chain cmdFromNSString   chain previous   returns chain previous  Example 2  provide conversion routines for an existing enum   also demonstrates using a settings string  and renaming the typename used in the functions   in myfile h      import  NSStringFromEnum h      define CAEdgeAntialiasingMask SETTINGS PARAMS CAEdgeAntialiasingMask mask EdgeMask edgeMask   interface NSString Enum Converters CAEdgeAntialiasingMask SETTINGS PARAMS      in myfile m         we can put this in the  m file as we are not defining a typedef  just the strings    define define CAEdgeAntialiasingMask enum    enum kCALayerLeftEdge    enum kCALayerRightEdge    enum kCALayerBottomEdge    enum kCALayerTopEdge      implementation NSString Enum Converters CAEdgeAntialiasingMask SETTINGS PARAMS

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I had a large enumerated type I wanted to convert it into an NSDictionary lookup  I ended up using sed from OSX terminal as     sed -E  s     space    1      alnum    1            1       1   g  ObservationType h   which can be read as   capture the first word on the line and output   word      word     This regex converts the enum in a header file named  ObservationType h  which contains   typedef enum   int        ObservationTypePulse   1      ObservationTypeRespRate   2      ObservationTypeTemperature   3                  into something like         ObservationTypePulse      ObservationTypePulse         ObservationTypeRespRate      ObservationTypeRespRate         ObservationTypeTemperature      ObservationTypeTemperature                 which can then be wrapped in a method using modern objective-c syntax       as explained by  yar1vn above  to create a NSDictionary lookup    - NSDictionary   observationDictionary       static NSDictionary  observationDictionary      static dispatch once t onceToken      dispatch once  amp onceToken             observationDictionary     NSDictionary alloc  initWithDictionary                                       ObservationTypePulse      ObservationTypePulse                                      ObservationTypeRespRate      ObservationTypeRespRate                                                                                                                          return observationDictionary      The dispatch once boiler-plate is just to ensure that the static variable is initialised in a thread-safe manner   Note  I found the sed regex expression on OSX odd - when I tried to use   to match  one or more  it didn t work and had to resort to using  1   as a replacement

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define typedef enum in class header   typedef enum       IngredientType text    0      IngredientType audio   1      IngredientType video   2      IngredientType image   3   IngredientType    write a method like this in class      NSString  typeStringForType  IngredientType  type      NSString  key    NSString stringWithFormat   IngredientType  i    type      return NSLocalizedString key  nil       have the strings inside Localizable strings file      IngredientType text     IngredientType 0     Text      IngredientType audio     IngredientType 1     Audio      IngredientType video     IngredientType 2     Video      IngredientType image     IngredientType 3     Image

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I use a variation on Barry Walk s answer  that in order of importance    Allows the compiler to check for missing case clauses  it can t if you have a default clause   Uses an Objective-C typical name  rather than a Java like name   Raises a specific exception  Is shorter    EG   -  NSString  describeFormatType  FormatType formatType           switch formatType            case JSON              return   JSON           case XML              return   XML           case Atom              return   Atom           case RSS              return   RSS              NSException raise NSInvalidArgumentException format   The given format type number   ld  is not known    formatType       return nil     Keep the compiler happy - does not understand above line never returns

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Another solution   typedef enum BollettinoMavRavTypes       AMZCartServiceOperationCreate      AMZCartServiceOperationAdd      AMZCartServiceOperationGet      AMZCartServiceOperationModify   AMZCartServiceOperation    define AMZCartServiceOperationValue operation     NSArray alloc  initWithObjects    CartCreate     CartAdd     CartGet     CartModify   nil  objectAtIndex  operation     In your method you can use   NSString  operationCheck   AMZCartServiceOperationValue operation

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Here is working -  https   github com ndpiparava ObjcEnumString    1st Approach  define enumString arg       arg     2nd Approach    NSString   secondApproach convertEnumToString  StudentProgressReport status        char  str   calloc sizeof kgood  1  sizeof char        int  goodsASInteger   NSSwapInt  unsigned int kgood       memcpy str   const void   amp goodsASInteger  sizeof goodsASInteger        NSLog    s   str       NSString  enumString    NSString stringWithUTF8String str       free str        return enumString       Third Approcah to enum to string NSString  const kNitin     Nitin   NSString  const kSara     Sara     typedef NS ENUM NSUInteger  Name        NameNitin      NameSara         NSString   thirdApproach convertEnumToString   Name weekday          strong NSString   pointer    NSString     amp kNitin      pointer   weekday      return  pointer

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pixel added the most brilliant answer here  https   stackoverflow com a 24255387 1364257 Please  upvote him   He uses the neat X macro from the 1960 s   I ve changed his code a bit for the modern ObjC    define X a  b  c  a b  enum ZZObjectType       XXOBJECTTYPE TABLE    typedef NSUInteger TPObjectType   undef X   define XXOBJECTTYPE TABLE   X ZZObjectTypeZero    0    ZZObjectTypeZero     X ZZObjectTypeOne      ZZObjectTypeOne     X ZZObjectTypeTwo      ZZObjectTypeTwo     X ZZObjectTypeThree      ZZObjectTypeThree       NSString  nameForObjectType  ZZObjectType objectType    define X a  b  c    a  c       NSDictionary  dict     XXOBJECTTYPE TABLE    undef X     return dict objectType       That s it  Clean and neat  Thanks to  pixel  https   stackoverflow com users 21804 pixel

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Combining  AdamRosenfield answer   Christoph comment and another trick to handle plain C enums I suggest      In a header file typedef enum     JSON   0             explicitly indicate starting index   XML    Atom    RSS     FormatTypeCount      keep track of the enum size automatically   FormatType  extern NSString  const FormatTypeName FormatTypeCount        In a source file NSString  const FormatTypeName FormatTypeCount         JSON      JSON      XML      XML      Atom      Atom      RSS      RSS           Usage NSLog        FormatTypeName XML      In the worst case - like if you change the enum but forget to change the names array - it will return nil for this key

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I would use the compiler s   string token  along with macros to make it all more compact     define ENUM START                            NSString  ret                     switch value      define ENUM CASE evalue                      case evalue                           ret     evalue                    break    define ENUM END                                                                return ret   NSString   CvtCBCentralManagerStateToString CBCentralManagerState value        ENUM START         ENUM CASE CBCentralManagerStateUnknown          ENUM CASE CBCentralManagerStateResetting          ENUM CASE CBCentralManagerStateUnsupported          ENUM CASE CBCentralManagerStateUnauthorized          ENUM CASE CBCentralManagerStatePoweredOff          ENUM CASE CBCentralManagerStatePoweredOn      ENUM END

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I made a sort of mix of all solutions found on this page to create mine  it s a kind of object oriented enum extension or  something   In fact if you need more than just constants  i e  integers   you probably need a model object  We re all talking about MVC  right    Just ask yourself the question before using this  am I right  don t you  in fact  need a real model object  initialized from a webservice  a plist  an SQLite database or CoreData    Anyway here comes the code  MPI is for  My Project Initials   everybody use this or their name  it seems     MyWonderfulType h    typedef NS ENUM NSUInteger  MPIMyWonderfulType        MPIMyWonderfulTypeOne   1      MPIMyWonderfulTypeTwo   2      MPIMyWonderfulTypeGreen   3      MPIMyWonderfulTypeYellow   4      MPIMyWonderfulTypePumpkin   5      import  lt Foundation Foundation h gt    interface MyWonderfulType   NSObject     NSString   displayNameForWonderfulType  MPIMyWonderfulType wonderfulType     NSString   urlForWonderfulType  MPIMyWonderfulType wonderfulType    end   And MyWonderfulType m     import  MyWonderfulType h    implementation MyWonderfulType     NSDictionary   myWonderfulTypeTitles       return                   MPIMyWonderfulTypeOne      One                  MPIMyWonderfulTypeTwo      Two                  MPIMyWonderfulTypeGreen      Green                  MPIMyWonderfulTypeYellow      Yellow                  MPIMyWonderfulTypePumpkin      Pumpkin                        NSDictionary   myWonderfulTypeURLs       return                   MPIMyWonderfulTypeOne      http   www theone com                  MPIMyWonderfulTypeTwo      http   www thetwo com                  MPIMyWonderfulTypeGreen      http   www thegreen com                  MPIMyWonderfulTypeYellow      http   www theyellow com                  MPIMyWonderfulTypePumpkin      http   www thepumpkin com                        NSString   displayNameForWonderfulType  MPIMyWonderfulType wonderfulType       return  MPIMyWonderfulType myWonderfulTypeTitles    wonderfulType          NSString   urlForWonderfulType  MPIMyWonderfulType wonderfulType       return  MPIMyWonderfulType myWonderfulTypeURLs    wonderfulType         end

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Given an enum definition like   typedef NS ENUM NSInteger  AssetIdentifier        Isabella      William      Olivia      We can define a macro to convert an enum value to its corresponding string  as shown below    define AssetIdentifier asset      AssetIdentifier identifier      switch  identifier      case asset    default    return   asset          asset    The switch statement used in the block is for type checking  and also to get the auto-complete support in Xcode

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First of all  with regards to FormatType JSON  JSON is not a member of FormatType  it s a possible value of the type  FormatType isn t even a composite type     it s a scalar   Second  the only way to do this is to create a mapping table  The more common way to do this in Objective-C is to create a series of constants referring to your  symbols   so you d have NSString  FormatTypeJSON     JSON  and so on

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My solution    edit  I ve added even a better solution at the end  using Modern Obj-C   1 Put names as keys in an array   Make sure the indexes are the appropriate enums  and in the right order  otherwise exception    note  names is a property synthesized as   names    code was not checked for compilation  but I used the same technique in my app   typedef enum     JSON    XML    Atom    RSS   FormatType      NSArray   names       static NSMutableArray    names   nil      static dispatch once t onceToken      dispatch once  amp onceToken              names    NSMutableArray arrayWithCapacity 4             names insertObject   JSON  atIndex JSON             names insertObject   XML  atIndex XML             names insertObject   Atom  atIndex Atom             names insertObject   RSS  atIndex RSS                return  names        NSString   nameForType  FormatType type       return   self names  objectAtIndex type          2 Using Modern Obj-C you we can use a dictionary to tie descriptions to keys in the enum Order DOES NOT matter    typedef NS ENUM NSUInteger  UserType        UserTypeParent   0      UserTypeStudent   1      UserTypeTutor   2      UserTypeUnknown   NSUIntegerMax        property  nonatomic  UserType type      NSDictionary   typeDisplayNames       return     UserTypeParent      Parent                  UserTypeStudent      Student                  UserTypeTutor      Tutor                  UserTypeUnknown      Unknown       -  NSString   typeDisplayName       return   self class  typeDisplayNames    self type        Usage  in a class instance method    NSLog         self typeDisplayName

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I like the  define way of doing this      Place this in your  h file  outside the  interface block  typedef enum       JPG      PNG      GIF      PVR   kImageType   define kImageTypeArray   JPEG     PNG     GIF     PowerVR   nil     Place this in the  m file  inside the  implementation block    A method to convert an enum to string - NSString   imageTypeEnumToString  kImageType enumVal       NSArray  imageTypeArray     NSArray alloc  initWithObjects kImageTypeArray       return  imageTypeArray objectAtIndex enumVal       source  source no longer available

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You can t do it easily   In C and Objective-C  enums are really just glorified integer constants   You ll have to generate a table of names yourself  or with some preprocessor abuse    For example      In a header file typedef enum FormatType       JSON      XML      Atom      RSS   FormatType   extern NSString   const FormatType toString        In a source file    initialize arrays with explicit indices to make sure     the string match the enums properly NSString   const FormatType toString            JSON      JSON        XML      XML        Atom      Atom        RSS      RSS            To convert enum to string  NSString  str   FormatType toString theEnumValue     The danger of this approach is that if you ever change the enum  you have to remember to change the array of names   You can solve this problem with some preprocessor abuse  but it s tricky and ugly   Also note that this assumes you have a valid enum constant   If you have an integer value from an untrusted source  you additionally need to do a check that your constant is valid  e g  by including a  past max  value in your enum  or by checking if it s less than the array length  sizeof FormatType toString    sizeof FormatType toString 0

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Every answer here basically says the same thing  create a regular enum and then use a custom getter to switch between strings   I employ a much simpler solution that is faster  shorter  and cleaner   using Macros      define kNames allNames   NSArray  lt NSString   gt        Alice     Bob     Eve     define kNames alice   NSString   kNames allNames 0    define kNames bob   NSString   kNames allNames 1    define kNames eve   NSString   kNames allNames 2     Then you can simply start to type kNam    and autocomplete will display the lists you desire   Additionally  if you want to handle logic for all the names at once you can simply fast enumerate the literal array in order  as follows   for  NSString  kName in kNames allNames      Lastly  the NSString casting in the macros ensures behavior similar to typedef     Enjoy

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Depending on your needs  you could alternatively use compiler directives to simulate the behaviour you are looking for     define JSON   JSON    define XML   XML    define Atom   Atom    define RSS   RSS    Just remember the usual compiler shortcomings   not type safe  direct copy-paste makes source file larger

[c] Convert objective-c typedef to its string equivalent

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