Question

Requirements:

• Must be able to use C strings as well as C++ strings
• Fast
• No maps
• No templates
• No direct lookup, i.e. index might be out of bounds.
• Index is not consecutive
• Enums and strings contained in one header file
• Only instantiate what you use.

This is what I have come up with so far:

- test.hh -  // Generic mapper //  // The idea here is to create a map between an integer and a string. // By including it inside a class we prevent every module which // includes this include file from creating their own instance. // struct Mapper_s {    int Idx;    const char *pStr; };  // Status enum State_t {    Running = 1,    Jumping = 6,     Singing = 12 };  struct State_s {    static const Mapper_s *GetpMap(void)    {        static Mapper_s Map[] =         {             { Running,   'Running' },             { Jumping,   'Jumping' },             { Singing,   'Singing' },             { 0,   0}         };         return Map;     }; };  - test.cc - // This is a generic function  const char *MapEnum2Str(int Idx, const Mapper_s *pMap) {     int i;     static const char UnknownStr[] = 'Unknown';      for (i = 0; pMap[i].pStr != 0; i++)     {         if (Idx == pMap[i].Idx)         {             return pMap[i].pStr;         }     }      return UnknownStr; }  int main() {    cout << 'State: ' << MapEnum2Str(State, State_s::GetpMap()) << endl;    return 0; } 

Any suggestions on how to improve this ?

I feel that the header file looks slightly cluttered…

Answer 1

Here is what I settled on. Using this technique all you need to do is to include a header file. You will only instantiate what you use. You could also store a perfect hash table instead of just Idx & pStr. This approach does not work in C.

file: e2str.hh

struct Mapper_s {     int Idx;     const char *pStr; };  #define ENUM2STR_BEGIN(x) struct x { static const Mapper_s *GetpMap(void) {  static const Enum2StrMap_s Map[] =  #define ENUM2STR_END      return Map; }; }  const char *MapEnum2Str(int Idx, const Mapper_s *pMap); 

file: mapper.hh

#include 'e2str.hh'  ENUM2STR_BEGIN(State_s)  {         { Running,   'Running' },         { Singing,   'Singing' },         { Jumping,   'Jumping' },         { 0, 0} }; ENUM2STR_END; 

file: test.cc

#include 'mapper.hh' int main() {    cout << 'State: ' << MapEnum2Str(State, State_s::GetpMap()) << endl;    return 0; }