Enumerations are widely used and we often need to convert enum values to strings (typically for recording values in logs) but there is no option at the language level or a utility in the standard library to make it possible. Therefore, developers are usually handcrafting their own solutions.<\/p>\n\n\n\n
Let’s say we have the following enum:<\/p>\n\n\n\n
enum person\n{\n funny, \n smart, \n intelligent\n};<\/pre>\n\n\n\nThe simplest solution to convert the values to strings is to write a function such as this:<\/p>\n\n\n\n
const char* to_string(person p)\n{\n switch(p)\n {\n case person::funny: return \"funny\";\n case person::smart: return \"smart\";\n case person::intelligent: return \"intelligent\";\n }\n return \"<none>\"; \/\/ or an empty string\n \/\/ or throw an exception\n}<\/pre>\n\n\n\nThe problems with this solution include the following:<\/p>\n\n\n\n
It would be helpful to have a sort of automatic way to generate such functions from the definition of an enumeration. A possible approach is using macros.<\/p>\n\n\n\n
A solution for this is explained in the article Converting C++ enums to strings<\/a> by Marcos Cardoso. In consists of several steps:<\/p>\n\n\n\n In this approach, we could create a The source file The The benefit of this solution is that the serialization function is generated automatically; you don’t have to maintain it manually. Whenever a new enumerator is added or an existing one is changed, the changes are reflected immediately in the However, this solution has a significant problem: in practice, many enumerations have explicit values defined for the enumerators (or only for some of them). These macros do not support defining such enumerations. But nothing stops us from expanding them to support both. Therefore, I modified the solution to the following:<\/p>\n\n\n\n The header In this case, the There is no significant different than the original macros, except for the name and the curly braces that are now part of the begin and end macros. Also, an underlying type, in this case However, should the enumeration explicitly define values, then the definition of the enum would change to the following:<\/p>\n\n\n\n The macros are similar, but they are suffixed with The source file Every time you define a new enumeration using this macros, you must include its header in this source file.<\/p>\n\n\n\n There is a slight change in usage, as the But macros are evil! <\/strong><\/p>\n\n\n\n We have heard this mantra so many times. The good news, for those of you that want something different, is that solutions that don’t require macros also exist. Such a solution is the library called Magic Enum C++<\/a>.<\/p>\n\n\n\n With this library, you define the enum without any macros, and use The reason I couldn’t use Magic Enum was that it defines some global objects. And then, it was used from the initialization of another global in another translation unit. And since there is no order defined for the initialization of globals in different translation units I could not rely on it. <\/p>\n\n\n\n But global are evil!<\/strong><\/p>\n\n\n\n Yes. So stop using The macros approach only works for unscoped enums. Magic Enum also works with scoped enums.<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" Enumerations are widely used and we often need to convert enum values to strings (typically for recording values in logs) but there is no option at the language level or a utility in the standard library to make it possible. Therefore, developers are usually handcrafting their own solutions. Let’s say we have the following enum: … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7],"tags":[451,645,554],"class_list":["post-4676","post","type-post","status-publish","format-standard","hentry","category-c","tag-c","tag-enums","tag-macros"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\tperson.h<\/code> header, with the following content:<\/p>\n\n\n\n#if (!defined(PERSON_H) || defined(GENERATE_ENUM_STRINGS))\n\n#if (!defined(GENERATE_ENUM_STRINGS))\n #define PERSON_H\n#endif\n\n#include \"EnumToString.h\"\n\nBEGIN_ENUM(person)\n{\n DECL_ENUM_ELEMENT(funny)\n DECL_ENUM_ELEMENT(smart)\n DECL_ENUM_ELEMENT(intelligent)\n}\nEND_ENUM(person)\n\n#endif PERSON_H<\/pre>\n\n\n\nEnumToString.cpp<\/code> would contain the following:<\/p>\n\n\n\n#define GENERATE_ENUM_STRINGS \/\/ Start string generation\n#include \"person.h\" \n#undef GENERATE_ENUM_STRINGS \/\/ Stop string generation<\/pre>\n\n\n\n
person<\/code> enum can be used as follows:<\/p>\n\n\n\n#include <iostream>\n#include \"person.h\"\n\nint main()\n{\n person p = person::funny;\n std::cout << p << '\\n';\n std::cout << GetStringperson(p) << '\\n';\n}<\/pre>\n\n\n\nGetStringX<\/code> function. <\/p>\n\n\n\nstringified_enum.h<\/code> contains the following definitions:<\/p>\n\n\n\n#pragma once\n\n#undef DECL_ENUM_ELEMENT\n#undef BEGIN_ENUM\n#undef END_ENUM\n\n#ifndef GENERATE_ENUM_STRINGS\n\n #define DECLARE_ENUM_ELEMENT(element) element,\n #define BEGIN_ENUM(ENUM_NAME, TYPE) typedef enum tag##ENUM_NAME : TYPE {\n #define BEGIN_ENUM_INT(ENUM_NAME) BEGIN_ENUM(ENUM_NAME, int)\n #define END_ENUM(ENUM_NAME) } ENUM_NAME; const char* ENUM_NAME##_as_string(enum tag##ENUM_NAME index);\n\n #define DECLARE_ENUM_ELEMENT_WITH_VALUE(element, value) element = value,\n #define BEGIN_ENUM_WITH_VALUES(ENUM_NAME, TYPE) BEGIN_ENUM(ENUM_NAME, TYPE)\n #define BEGIN_ENUM_WITH_VALUES_INT(ENUM_NAME) BEGIN_ENUM(ENUM_NAME, int)\n #define END_ENUM_WITH_VALUES(ENUM_NAME) END_ENUM(ENUM_NAME)\n\n#else\n #define NO_VALUE \"<none>\"\n\n #define DECLARE_ENUM_ELEMENT(element) #element,\n\n #define BEGIN_ENUM(ENUM_NAME, TYPE) enum tag##ENUM_NAME : TYPE;\\\nconst char* ENUM_NAME##_as_string(enum tag##ENUM_NAME value) {\\\n std::size_t index = static_cast<std::size_t>(value);\\\n static const char* s_##ENUM_NAME[] = {\n\n #define BEGIN_ENUM_INT(ENUM_NAME) BEGIN_ENUM(ENUM_NAME, int)\n\n #define END_ENUM(ENUM_NAME) };\\\n static const std::size_t s_##ENUM_NAME_len = sizeof(s_##ENUM_NAME)\/sizeof(const char*);\\\n if(index >=0 && index < s_##ENUM_NAME_len)\\\n return s_##ENUM_NAME[index]; \\\n return NO_VALUE;\\\n}\n\n #define DECLARE_ENUM_ELEMENT_WITH_VALUE(element, value) {value, #element},\n\n #define BEGIN_ENUM_WITH_VALUES(ENUM_NAME, TYPE) enum tag##ENUM_NAME : TYPE;\\\nconst char* ENUM_NAME##_as_string(enum tag##ENUM_NAME value) {\\\n std::map<TYPE, const char*> sv = {\n\n #define BEGIN_ENUM_WITH_VALUES_INT(ENUM_NAME) BEGIN_ENUM_WITH_VALUES(ENUM_NAME, int)\n\n #define END_ENUM_WITH_VALUES(ENUM_NAME) };\\\n auto it = sv.find(value);\\\n if (it != sv.end())\\\n return it->second;\\\n return NO_VALUE;\\\n}\n\n#endif<\/pre>\n\n\n\nperson.h<\/code> header containing the person<\/code> enum definition changes to the following:<\/p>\n\n\n\n#if (!defined(PERSON_H) || defined(GENERATE_ENUM_STRINGS))\n\n#if (!defined(GENERATE_ENUM_STRINGS))\n #define PERSON_H\n#endif\n\n#include \"stringified_enum.h\"\n\nBEGIN_ENUM(person, int)\n DECLARE_ENUM_ELEMENT(funny)\n DECLARE_ENUM_ELEMENT(smart)\n DECLARE_ENUM_ELEMENT(intelligent)\nEND_ENUM(person)\n\n#endif PERSON_H<\/pre>\n\n\n\n
int<\/code>, is specified explicitly. There is a macro BEGIN_ENUM_INT<\/code> that implicitly uses int<\/code> for this purpose.<\/p>\n\n\n\nBEGIN_ENUM_WITH_VALUES(person, int)\n DECLARE_ENUM_ELEMENT_WITH_VALUE(funny, 1)\n DECLARE_ENUM_ELEMENT_WITH_VALUE(smart, 3)\n DECLARE_ENUM_ELEMENT_WITH_VALUE(intelligent, 7)\nEND_ENUM_WITH_VALUES(person)<\/pre>\n\n\n\n
_WITH_VALUE<\/code>\/_WITH_VALUES<\/code>. DECLARE_ENUM_ELEMENT_WITH_VALUE<\/code> requires specifying a value for the enumerator.<\/p>\n\n\n\nstringified_enum.cpp<\/code> must be compiled with the rest of the program and contains the following:<\/p>\n\n\n\n#define GENERATE_ENUM_STRINGS \/\/ Start string generation\n\n#include <map>\n\n#include \"person.h\"\n\n#undef GENERATE_ENUM_STRINGS \/\/ Stop string generation <\/pre>\n\n\n\n
GetStringX<\/code> serialization function is now called x_as_string<\/code>:<\/p>\n\n\n\n#include <iostream>\n#include \"person.h\"\n\nint main()\n{\n person p = person::funny;\n std::cout << p << '\\n';\n std::cout << person_as_string(p) << '\\n';\n}<\/pre>\n\n\n\nmagic_enum::enum_name()<\/code> to get the name of an enumerator:<\/p>\n\n\n\n#include <iostream>\n#include \"magicenum.h\"\n\nenum person\n{\n funny,\n smart,\n intelligent\n};\n\nint main()\n{\n person p = person::funny;\n std::cout << p << '\\n';\n std::cout << magic_enum::enum_name(p) << '\\n';\n}<\/pre>\n\n\n\nstd::cout<\/code>.<\/p>\n\n\n\n