C Print out enum value as text

Question

If i have an enum like this  enum Errors  ErrorA 0  ErrorB  ErrorC     Then i want to print out to console  Errors anError   ErrorA  cout lt  lt anError     0 will be printed   but what i want is the text  ErrorA   can i do it without using if switch  And what is your solution for this

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You could use a stl map container      typedef map lt Errors  string gt  ErrorMap   ErrorMap m  m insert ErrorMap  value type ErrorA   ErrorA     m insert ErrorMap  value type ErrorB   ErrorB     m insert ErrorMap  value type ErrorC   ErrorC      Errors error   ErrorA   cout  lt  lt  m error   lt  lt  endl

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How about this       enum class ErrorCodes   int            InvalidInput   0             std  cout  lt  lt    int error    0    InvalidInput         lt  lt  std  endl    etc    I know this is a highly contrived example but I think it has application where applicable and needed and is certainly shorter than writing a script for it

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You can use a simpler pre-processor trick if you are willing to list your enum entries in an external file      file  errors def       syntax  ERROR DEF name  value     ERROR DEF ErrorA  0x1  ERROR DEF ErrorB  0x2  ERROR DEF ErrorC  0x4    Then in a source file  you treat the file like an include file  but you define what you want the ERROR DEF to do   enum Errors    define ERROR DEF x y  x   y   include  errors def   undef ERROR DEF     static inline std  ostream  amp  operator  lt  lt   std  ostream  amp o  Errors e        switch  e         define ERROR DEF x y  case y  return o  lt  lt   x     lt  lt  y  lt  lt            include  errors def       undef ERROR DEF     default  return o  lt  lt   unknown    lt  lt  e  lt  lt                 If you use some source browsing tool  like cscope   you ll have to let it know about the external file

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This solution doesn t require you to use any data structures or make a different file   Basically  you define all your enum values in a  define  then use them in the operator  lt  lt   Very similar to  jxh s answer   ideone link for final iteration  http   ideone com hQTKQp  Full code    include  lt iostream gt    define ERROR VALUES ERROR VALUE NO ERROR   ERROR VALUE FILE NOT FOUND   ERROR VALUE LABEL UNINITIALISED   enum class Error    define ERROR VALUE NAME  NAME      ERROR VALUES  undef ERROR VALUE     inline std  ostream amp  operator lt  lt  std  ostream amp  os  Error err        int errVal   static cast lt int gt  err       switch  err         define ERROR VALUE NAME  case Error  NAME  return os  lt  lt       lt  lt  errVal  lt  lt       NAME      ERROR VALUES  undef ERROR VALUE     default             If the error value isn t found  shouldn t happen          return os  lt  lt  errVal           int main         std  cout  lt  lt   Error     lt  lt  Error  NO ERROR  lt  lt  std  endl      std  cout  lt  lt   Error     lt  lt  Error  FILE NOT FOUND  lt  lt  std  endl      std  cout  lt  lt   Error     lt  lt  Error  LABEL UNINITIALISED  lt  lt  std  endl      return 0      Output   Error   0 NO ERROR Error   1 FILE NOT FOUND Error   2 LABEL UNINITIALISED   A nice thing about doing it this way is that you can also specify your own custom messages for each error if you think you need them    include  lt iostream gt    define ERROR VALUES ERROR VALUE NO ERROR   Everything is fine    ERROR VALUE FILE NOT FOUND   File is not found    ERROR VALUE LABEL UNINITIALISED   A component tried to the label before it was initialised    enum class Error    define ERROR VALUE NAME DESCR  NAME      ERROR VALUES  undef ERROR VALUE     inline std  ostream amp  operator lt  lt  std  ostream amp  os  Error err        int errVal   static cast lt int gt  err       switch  err         define ERROR VALUE NAME DESCR  case Error  NAME  return os  lt  lt       lt  lt  errVal  lt  lt       NAME  lt  lt       lt  lt  DESCR      ERROR VALUES  undef ERROR VALUE     default          return os  lt  lt  errVal           int main         std  cout  lt  lt   Error     lt  lt  Error  NO ERROR  lt  lt  std  endl      std  cout  lt  lt   Error     lt  lt  Error  FILE NOT FOUND  lt  lt  std  endl      std  cout  lt  lt   Error     lt  lt  Error  LABEL UNINITIALISED  lt  lt  std  endl      return 0      Output   Error   0 NO ERROR  Everything is fine Error   1 FILE NOT FOUND  File is not found Error   2 LABEL UNINITIALISED  A component tried to the label before it was initialised   If you like making your error codes descriptions very descriptive  you might not want them in production builds  Turning them off so only the value is printed is easy   inline std  ostream amp  operator lt  lt  std  ostream amp  os  Error err        int errVal   static cast lt int gt  err       switch  err             ifndef PRODUCTION BUILD    Don t print out names in production builds      define ERROR VALUE NAME DESCR  case Error  NAME  return os  lt  lt       lt  lt  errVal  lt  lt       NAME  lt  lt       lt  lt  DESCR          ERROR VALUES      undef ERROR VALUE      endif     default          return os  lt  lt  errVal            Output   Error  0 Error  1 Error  2   If this is the case  finding error number 525 would be a PITA  We can manually specify the numbers in the initial enum like this    define ERROR VALUES ERROR VALUE NO ERROR  0   Everything is fine    ERROR VALUE FILE NOT FOUND  1   File is not found    ERROR VALUE LABEL UNINITIALISED  2   A component tried to the label before it was initialised    ERROR VALUE UKNOWN ERROR  -1   Uh oh    enum class Error    define ERROR VALUE NAME VALUE DESCR  NAME VALUE      ERROR VALUES  undef ERROR VALUE     inline std  ostream amp  operator lt  lt  std  ostream amp  os  Error err        int errVal   static cast lt int gt  err       switch  err         ifndef PRODUCTION BUILD    Don t print out names in production builds  define ERROR VALUE NAME VALUE DESCR  case Error  NAME  return os  lt  lt       VALUE       NAME  lt  lt       lt  lt  DESCR      ERROR VALUES  undef ERROR VALUE  endif     default          return os  lt  lt errVal              ERROR VALUES  undef ERROR VALUE  endif     default                   If the error value isn t found  shouldn t happen          return os  lt  lt  static cast lt int gt  err           break                  Output   Error   0 NO ERROR  Everything is fine Error   1 FILE NOT FOUND  File is not found Error   2 LABEL UNINITIALISED  A component tried to the label before it was initialised Error   -1 UKNOWN ERROR  Uh oh

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Using map    include  lt iostream gt   include  lt map gt   include  lt string gt   enum Errors  ErrorA 0  ErrorB  ErrorC    std  ostream amp  operator lt  lt  std  ostream amp  out  const Errors value       static std  map lt Errors  std  string gt  strings      if  strings size      0    define INSERT ELEMENT p  strings p     p         INSERT ELEMENT ErrorA                INSERT ELEMENT ErrorB                INSERT ELEMENT ErrorC                 undef INSERT ELEMENT               return out  lt  lt  strings value      int main int argc  char   argv       std  cout  lt  lt  ErrorA  lt  lt  std  endl  lt  lt  ErrorB  lt  lt  std  endl  lt  lt  ErrorC  lt  lt  std  endl      return 0         Using array of structures with linear search    include  lt iostream gt   include  lt string gt   enum Errors  ErrorA 0  ErrorB  ErrorC    std  ostream amp  operator lt  lt  std  ostream amp  out  const Errors value    define MAPENTRY p   p   p      const struct MapEntry          Errors value          const char  str        entries               MAPENTRY ErrorA           MAPENTRY ErrorB           MAPENTRY ErrorC            ErrorA  0   doesn t matter what is used instead of ErrorA here            undef MAPENTRY     const char  s   0      for  const MapEntry  i   entries  i- gt str  i             if  i- gt value    value               s   i- gt str              break                       return out  lt  lt  s     int main int argc  char   argv       std  cout  lt  lt  ErrorA  lt  lt  std  endl  lt  lt  ErrorB  lt  lt  std  endl  lt  lt  ErrorC  lt  lt  std  endl      return 0         Using switch case    include  lt iostream gt   include  lt string gt   enum Errors  ErrorA 0  ErrorB  ErrorC    std  ostream amp  operator lt  lt  std  ostream amp  out  const Errors value       const char  s   0   define PROCESS VAL p  case p   s    p  break      switch value           PROCESS VAL ErrorA                PROCESS VAL ErrorB                PROCESS VAL ErrorC          undef PROCESS VAL      return out  lt  lt  s     int main int argc  char   argv       std  cout  lt  lt  ErrorA  lt  lt  std  endl  lt  lt  ErrorB  lt  lt  std  endl  lt  lt  ErrorC  lt  lt  std  endl      return 0

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Here is an example based on Boost Preprocessor    include  lt iostream gt    include  lt boost preprocessor punctuation comma hpp gt   include  lt boost preprocessor control iif hpp gt   include  lt boost preprocessor comparison equal hpp gt   include  lt boost preprocessor stringize hpp gt   include  lt boost preprocessor seq for each hpp gt   include  lt boost preprocessor seq size hpp gt   include  lt boost preprocessor seq seq hpp gt     define DEFINE ENUM name  values                                    enum name                                                           BOOST PP SEQ FOR EACH DEFINE ENUM VALUE    values                                                                                 inline const char  format   name name val                           switch  val                                                         BOOST PP SEQ FOR EACH DEFINE ENUM FORMAT    values              default                                                               return 0                                                                                                                          define DEFINE ENUM VALUE r  data  elem                             BOOST PP SEQ HEAD elem                                            BOOST PP IIF BOOST PP EQUAL BOOST PP SEQ SIZE elem   2                           BOOST PP SEQ TAIL elem                             BOOST PP COMMA     define DEFINE ENUM FORMAT r  data  elem                  case BOOST PP SEQ HEAD elem                             return BOOST PP STRINGIZE BOOST PP SEQ HEAD elem      DEFINE ENUM Errors                ErrorA  0                 ErrorB                 ErrorC     int main       std  cout  lt  lt  format Errors ErrorB   lt  lt  std  endl

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There has been a discussion here which might help  Is there a simple way to convert C   enum to string   UPDATE  Here s a script for Lua which creates an operator lt  lt  for each named enum it encounters  This might need some work to make it work for the less simple cases  1    function make enum printers s      for n body in string gmatch s  enum s    w     s   b      do     print  ostream amp  operator lt  lt  ostream  amp o    n    n    switch n          for k in string gmatch body     w            do     print    case    k     return o lt  lt     k            end     print    default  return o lt  lt   invalid value             end end  local f io open arg 1   r   local s f read   a   make enum printers s    Given this input   enum Errors  ErrorA 0  ErrorB  ErrorC    enum Sec       X 1 Y X foo bar X 1 Z      It produces   ostream amp  operator lt  lt  ostream  amp o Errors n    switch n     case ErrorA  return o lt  lt  ErrorA     case ErrorB  return o lt  lt  ErrorB     case ErrorC  return o lt  lt  ErrorC     default  return o lt  lt   invalid value       ostream amp  operator lt  lt  ostream  amp o Sec n    switch n     case X  return o lt  lt  X     case Y  return o lt  lt  Y     case foo bar  return o lt  lt  foo bar     case Z  return o lt  lt  Z     default  return o lt  lt   invalid value         So that s probably a start for you    1  enums in different or non-namespace scopes  enums with initializer expressions which contain a komma  etc

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For this problem  I do a help function like this   const char  name Id id        struct Entry           Id id          const char  name             static const Entry entries                 ErrorA   ErrorA               ErrorB   ErrorB               0  0             for  int it   0  it  lt  gui  SiCount    it            if  entries it  id    id                return entries it  name                     return 0      Linear search is usually more efficient than std  map for small collections like this

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This is a good way   enum Rank   ACE   1  DEUCE  TREY  FOUR  FIVE  SIX  SEVEN  EIGHT  NINE  TEN  JACK  QUEEN  KING      Print it with an array of character arrays  const char  rank txt       Ace    Deuce    Trey    Four    Five    Six    Seven    Eight    Nine    Ten    Jack    Four    King        Like this  std  cout  lt  lt  rank txt m rank - 1

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Use an array or vector of strings with matching values   char  ErrorTypes            errorA        errorB        errorC      cout  lt  lt  ErrorTypes anError       EDIT  The solution above is applicable when the enum is contiguous  i e  starts from 0 and there are no assigned values  It will work perfectly with the enum in the question   To further proof it for the case that enum doesn t start from 0  use   cout  lt  lt  ErrorTypes anError - ErrorA

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Use the preprocessor    define VISIT ERROR FIRST  MIDDLE  LAST        FIRST ErrorA  MIDDLE ErrorB     MIDDLE ErrorB2     LAST ErrorC   enum Errors        define ENUMFIRST ERROR E   E 0       define ENUMMIDDLE ERROR E  E       define ENUMLAST ERROR E    E     VISIT ERROR ENUMFIRST ERROR  ENUMMIDDLE ERROR  ENUMLAST ERROR         you might undefine the 3 macros defined above     std  string toString Error e        switch e             define CASERETURN ERROR E   case E  return  E      VISIT ERROR CASERETURN ERROR  CASERETURN ERROR  CASERETURN ERROR         you might undefine the above macro         note that this will produce compile-time error for synonyms in enum         handle those  if you have any  in a distinct macro      default          throw my favourite exception              The advantage of this approach is that     - it s still simple to understand  yet    - it allows for various visitations  not just string   If you re willing to drop the first  craft yourself a FOREACH   macro  then  define ERROR VALUES    ErrorA  ErrorB  ErrorC  and write your visitors in terms of FOREACH    Then try to pass a code review

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I use a string array whenever I define an enum   Profile h   pragma once  struct Profile       enum Value               Profile1          Profile2              struct StringValueImplementation               const wchar t  operator   const Profile  Value profile                        switch  profile                            case Profile  Profile1  return L Profile1               case Profile  Profile2  return L Profile2               default  ASSERT false   return NULL                                      static StringValueImplementation StringValue       Profile cpp   include  Profile h   Profile  StringValueImplementation Profile  StringValue

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Please take a look at this post   enum to string in modern C  11   C  14   C  17 and future C  20  drz

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include  lt iostream gt  using std  cout  using std  endl   enum TEnum      EOne    ETwo    EThree    ELast      define VAR NAME HELPER name   name  define VAR NAME x  VAR NAME HELPER x    define CHECK STATE STR x  case x  return VAR NAME x    const char  State2Str const TEnum state      switch state          CHECK STATE STR EOne       CHECK STATE STR ETwo       CHECK STATE STR EThree       CHECK STATE STR ELast       default        return  Invalid          int main       int myInt 12345    cout  lt  lt  VAR NAME EOne       lt  lt  VAR NAME myInt   lt  lt  endl     for int i   -1  i  lt  5    i      cout  lt  lt  i  lt  lt       lt  lt  State2Str  TEnum i   lt  lt  endl    return 0

[c++] C++: Print out enum value as text

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