How to Efficiently Map C Enums to Strings?

How to Easily Map C Enums to Strings

When utilizing enums defined in third-party library headers, it becomes necessary to establish a mechanism for converting enum values to user-defined strings and vice versa.

Standard Approach

A straightforward approach involves creating a series of functions:

enum MyEnum {VAL1, VAL2,VAL3};

String getStringFromEnum(MyEnum e)
{
  switch e
  {
  case VAL1: return "Value 1";
  case VAL2: return "Value 2";
  case VAL1: return "Value 3";
  default: throw Exception("Bad MyEnum");
  }
}

This method, however, lacks elegance and resembles a C-style approach.

Template-Based Solution

A more sophisticated approach utilizes templates:

std::map<MyEnum, char const*> MyMap;
//...
MyMap.insert(std::make_pair(VAL1, "Value 1"));
//...
char const* enumString = MyMap[e];

This method provides a clean and efficient mapping mechanism.

map_init Helper Class

For syntactic convenience, the following helper class can be used:

template<typename T> struct map_init_helper
{
    map_init_helper(T&amp; d) : data(d) {}
    T&amp; data;
    map_init_helper&amp; operator() (typename T::key_type const&amp; key, typename T::mapped_type const&amp; value)
    {
        data[key] = value;
        return *this;
    }
};

template<typename T> map_init_helper<T> map_init(T&amp; item)
{
    return map_init_helper<T>(item);
}

With this helper, the mapping can be accomplished as follows:

std::map<MyEnum, char const*> MyMap;
map_init(MyMap)
    (VAL1, "Value 1")
    (VAL2, "Value 2")
    (VAL3, "Value 3");

This simplified syntax eliminates the need for verbose insert statements.

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