Question

I have an array of constant data like following:

enum Language {GERMAN=LANG_DE, ENGLISH=LANG_EN, ...};
struct LanguageName {
    ELanguage language;
    const char *name;
};

const Language[] languages = {
    GERMAN, "German",
    ENGLISH, "English",
    .
    .
    .
};

When I have a function which accesses the array and find the entry based on the Language enum parameter. Should I write a loop to find the specific entry in the array or are there better ways to do this.

I know I could add the LanguageName-objects to an std::map but wouldn’t this be overkill for such a simple problem? I do not have an object to store the std::map so the map would be constructed for every call of the function.

What way would you recommend?

Is it better to encapsulate this compile time constant array in a class which handles the lookup?

Answer 1

If the enum values are contiguous starting from 0, use an array with the enum as index.

If not, this is what I usually do:

const char* find_language(Language lang)
{
  typedef std::map<Language,const char*> lang_map_type;
  typedef lang_map_type::value_type lang_map_entry_type;

  static const lang_map_entry_type lang_map_entries[] = { /*...*/  }
  static const lang_map_type lang_map( lang_map_entries
                                     , lang_map_entries + sizeof(lang_map_entries)
                                                        / sizeof(lang_map_entries[0]) );
  lang_map_type::const_iterator it = lang_map.find(lang);
  if( it == lang_map.end() ) return NULL;
  return it->second;
}

If you consider a map for constants, always also consider using a vector.

Function-local statics are a nice way to get rid of a good part of the dependency problems of globals, but are dangerous in a multi-threaded environment. If you’re worried about that, you might rather want to use globals:

typedef std::map<Language,const char*> lang_map_type;
typedef lang_map_type::value_type lang_map_entry_type;

const lang_map_entry_type lang_map_entries[] = { /*...*/  }
const lang_map_type lang_map( lang_map_entries
                            , lang_map_entries + sizeof(lang_map_entries)
                                               / sizeof(lang_map_entries[0]) );

const char* find_language(Language lang)
{
  lang_map_type::const_iterator it = lang_map.find(lang);
  if( it == lang_map.end() ) return NULL;
  return it->second;
}