Intelligent 'enum's in C++ Applications

Monday Dec 29th 2003 by Lloyd Williamsen

Representing Enums as C++ classes.

Environment: C++
Keywords: Enumerations, strings, integers, automatic defaults.

On several occasions in the past I have found C++ enumerations lacking. Enums need an automatic default and Enums need string functionality along with the integer value, particularily in applications that interact with a user either on a GUI or in an error message.

I thus concieved the idea to represent Enums as C++ classes which provide all the standard functionality of an enum, by overiding the relevant operators. And then adding the extra functionality desired.

Rather than writing these classes, a utility which translates standard Enum declerations to such classes would be great. Along with the idea, I have supplied a utility EC (enum compiler) that will do the job on Microsoft platforms.

In other words if I supply the following:

  enum EState
    Unknown = 0,
    Solid = 1,  // Solid Matter
    Liquid = 2, // "Liquid Matter "
    Gas,        /* Vapour */
One could generate a class as follows:
  class EState
   // EState::Unknown,Solid,Liquid,Gas,
   enum Enum
     Unknown = 0,
     Solid   = 1,  // "Solid Matter"
     Liquid  = 2,  // "Liquid Matter "
     Gas,          // "Vapour"

   Enum operator=(int i);
   operator int () const;

   Enum operator=(const char* sz);
   bool operator==(const char* sz);
   operator const char* () const;


  EState::Map_t EState::m_Map[] =
      {Unknown, "Unknown"},
      {Solid,   "Solid Matter"},
      {Liquid,  "Liquid Matter "},
      {Gas,     "Vapour"}
which could then be used as an "intelligent" Enum.

These "intelligent" Enums can be used as follows:

  int X;
  EState eState;
  eState = X;
  if(eState == EState::Unknown) {...}
  printf("eState is '%s' [%d]", (const char*)eState, eState);
  eState = "Text String";
  if(eState == EState::Unknown) ...
making some parts of coding simpler and more understandable.


Download EnumCompiler utility(Microsoft) and demo project - 16 Kb
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