I have long been looking for an elegant, one-line solution to mapenum to strings automatically, for use with the<< and>> stream operators.

I know that a lot of macros have been proposed to achieve that, but I never found a really simple scheme, with only one macro call.

This is my attempt, and I would be interested to discuss the advantages and limitations of this approach...

Definitions:

#include <string>#include <iostream>#include <stdexcept>#include <algorithm>#include <iterator>#include <sstream>#include <vector>#define MAKE_STRING(str, ...) #str, MAKE_STRING1_(__VA_ARGS__)#define MAKE_STRING1_(str, ...) #str, MAKE_STRING2_(__VA_ARGS__)#define MAKE_STRING2_(str, ...) #str, MAKE_STRING3_(__VA_ARGS__)#define MAKE_STRING3_(str, ...) #str, MAKE_STRING4_(__VA_ARGS__)#define MAKE_STRING4_(str, ...) #str, MAKE_STRING5_(__VA_ARGS__)#define MAKE_STRING5_(str, ...) #str, MAKE_STRING6_(__VA_ARGS__)#define MAKE_STRING6_(str, ...) #str, MAKE_STRING7_(__VA_ARGS__)#define MAKE_STRING7_(str, ...) #str, MAKE_STRING8_(__VA_ARGS__)#define MAKE_STRING8_(str, ...) #str, MAKE_STRING9_(__VA_ARGS__)#define MAKE_STRING9_(str, ...) #str, MAKE_STRING10_(__VA_ARGS__)#define MAKE_STRING10_(str) #str#define MAKE_ENUM(name, ...) MAKE_ENUM_(, name, __VA_ARGS__)#define MAKE_CLASS_ENUM(name, ...) MAKE_ENUM_(friend, name, __VA_ARGS__)#define MAKE_ENUM_(attribute, name, ...) name { __VA_ARGS__ }; \    attribute std::istream& operator>>(std::istream& is, name& e) { \        const char* name##Str[] = { MAKE_STRING(__VA_ARGS__) }; \        std::string str; \        std::istream& r = is >> str; \        const size_t len = sizeof(name##Str)/sizeof(name##Str[0]); \        const std::vector<std::string> enumStr(name##Str, name##Str + len); \        const std::vector<std::string>::const_iterator it = std::find(enumStr.begin(), enumStr.end(), str); \        if (it != enumStr.end())\            e = name(it - enumStr.begin()); \        else \            throw std::runtime_error("Value \"" + str + "\" is not part of enum "#name); \        return r; \    }; \    attribute std::ostream& operator<<(std::ostream& os, const name& e) { \        const char* name##Str[] = { MAKE_STRING(__VA_ARGS__) }; \        return (os << name##Str[e]); \    }

Usage:

enum MAKE_ENUM(Test3, Item13, Item23, Item33, Itdsdgem43);class Essai {public:    enum MAKE_CLASS_ENUM(Test, Item1, Item2, Item3, Itdsdgem4);};int main() {    std::cout << Essai::Item1 << std::endl;    Essai::Test ddd = Essai::Item1;    std::cout << ddd << std::endl;    std::istringstream strm("Item2");    strm >> ddd;    std::cout << (int) ddd << std::endl;    std::cout << ddd << std::endl;}

• \$\begingroup\$Shouldn'tEssai just be astruct since its only member ispublic?\$\endgroup\$

  Jamal

  – Jamal

  2014-03-07 19:10:01 +00:00

  CommentedMar 7, 2014 at 19:10
• \$\begingroup\$You may want to see this template version I wrote.codereview.stackexchange.com/a/14315/507 It maps enum to strings and strings back to enums. All you need to do is define an array of strings for each enum and the template magic does the rest.\$\endgroup\$

  Loki Astari

  – Loki Astari

  2014-03-08 02:07:51 +00:00

  CommentedMar 8, 2014 at 2:07
• \$\begingroup\$There are only a few real uses for macros in C++ this is not one of them.\$\endgroup\$

  Loki Astari

  – Loki Astari

  2014-03-08 02:12:11 +00:00

  CommentedMar 8, 2014 at 2:12
• \$\begingroup\$@Jamal: it's just an example to show an usage within a class... @LokiAstari: your template version is really nice. But, it requires conversion functionsenumToString() andenumFromString(). The goal here was to provideenum directly with the stream serialization operators<< and>>.\$\endgroup\$

  OlivierB

  – OlivierB

  2014-03-08 10:13:53 +00:00

  CommentedMar 8, 2014 at 10:13

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