enum to string in modern C++11 / C++14 / C++17 and future C++20

Question

Contrary to all other similar questions, this question is about using the new C++ features.

• 2008 c Is there a simple way to convert C++ enum to string?
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Answer 1

Well, yet another option. A typical use case is where you need constants for the HTTP verbs as well as using its string version values.

The example:

int main () {

  VERB a = VERB::GET;
  VERB b = VERB::GET;
  VERB c = VERB::POST;
  VERB d = VERB::PUT;
  VERB e = VERB::DELETE;


  std::cout << a.toString() << std::endl;

  std::cout << a << std::endl;

  if ( a == VERB::GET ) {
    std::cout << "yes" << std::endl;
  }

  if ( a == b ) {
    std::cout << "yes" << std::endl;
  }

  if ( a != c ) {
    std::cout << "no" << std::endl;
  }

}

The VERB class:

// -----------------------------------------------------------
// -----------------------------------------------------------
class VERB {

private:

  // private constants
  enum Verb {GET_=0, POST_, PUT_, DELETE_};

  // private string values
  static const std::string theStrings[];

  // private value
  const Verb value;
  const std::string text;

  // private constructor
  VERB (Verb v) :
  value(v), text (theStrings[v])
  {
    // std::cout << " constructor \n";
  }

public:

  operator const char * ()  const { return text.c_str(); }

  operator const std::string ()  const { return text; }

  const std::string toString () const { return text; }

  bool operator == (const VERB & other) const { return (*this).value == other.value; }

  bool operator != (const VERB & other) const { return ! ( (*this) == other); }

  // ---

  static const VERB GET;
  static const VERB POST;
  static const VERB PUT;
  static const VERB DELETE;

};

const std::string VERB::theStrings[] = {"GET", "POST", "PUT", "DELETE"};

const VERB VERB::GET = VERB ( VERB::Verb::GET_ );
const VERB VERB::POST = VERB ( VERB::Verb::POST_ );
const VERB VERB::PUT = VERB ( VERB::Verb::PUT_ );
const VERB VERB::DELETE = VERB ( VERB::Verb::DELETE_ );
// end of file