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

If your enum looks like

enum MyEnum
{
  AAA = -8,
  BBB = '8',
  CCC = AAA + BBB
};

You can move the content of the enum to a new file:

AAA = -8,
BBB = '8',
CCC = AAA + BBB

And then the values can be surrounded by a macro:

// default definition
#ifned ITEM(X,Y)
#define ITEM(X,Y)
#endif

// Items list
ITEM(AAA,-8)
ITEM(BBB,'8')
ITEM(CCC,AAA+BBB)

// clean up
#undef ITEM

Next step may be include the items in the enum again:

enum MyEnum
{
  #define ITEM(X,Y) X=Y,
  #include "enum_definition_file"
};

And finally you can generate utility functions about this enum:

std::string ToString(MyEnum value)
{
  switch( value )
  {
    #define ITEM(X,Y) case X: return #X;
    #include "enum_definition_file"
  }

  return "";
}

MyEnum FromString(std::string const& value)
{
  static std::map converter
  {
    #define ITEM(X,Y) { #X, X },
    #include "enum_definition_file"
  };

  auto it = converter.find(value);
  if( it != converter.end() )
    return it->second;
  else
    throw std::runtime_error("Value is missing");
}

The solution can be applied to older C++ standards and it does not use modern C++ elements but it can be used to generate lot of code without too much effort and maintenance.