C++ compile-time enum to string, iteration, in a single header file


Better Enums   Try online Travis status AppVeyor status

Reflective compile-time enum library with clean syntax, in a single header file, and without dependencies.

Better Enums code overview

In C++11, everything can be used at compile time. You can convert your enums, loop over them, find their max, statically enforce conventions, and pass along the results as template arguments or to constexpr functions. All the reflection is available for your metaprogramming needs.

The interface is the same for C++98 — you just have to use most of it at run time only. This library does provide scoped and sized enums, something not built into C++98.

See the project page for full documentation.


Simply add enum.h to your project.

Additional features

  • Uses only standard C++, though, for C++98, variadic macro support is required (major compilers have it).
  • Supported and tested on clang, gcc, and msvc.
  • Fast compilation. You have to declare a few dozen enums to slow down your compiler as much as only including iostream does.
  • Use any initializers and sparse ranges, just like with a built-in enum.
  • Control over size and alignment — you choose the representation type.
  • Stream operators.
  • Does not use the heap and can be compiled with exceptions disabled, for use in minimal freestanding environments.


  1. The biggest limitation is that the BETTER_ENUM macro can't be used inside a class. This seems difficult to remove. There is a workaround with typedef (or C++11 using):

    BETTER_ENUM(SomePrefix_Color, uint8_t, Red, Green, Blue)
    struct triplet {
        typedef SomePrefix_Color    Color;
        Color                       r, g, b;
    triplet::Color  color;

    You can, however, use BETTER_ENUM inside a namespace.

  2. The macro has a soft limit of 64 declared constants. You can extend it by following these instructions. Ultimately, the number of constants is limited by your compiler's maximum macro argument count.

  3. In some cases, it is necessary to prefix constants such as Channel::Red with a + to explicitly promote them to type Channel. For example, if you are doing a comparison:

    channel == +Channel::Red
  4. On msvc, you may need to enable warning C4062 to get switch case exhaustiveness checking.


The original version of the library was developed by the author in the winter of 2012-2013 at Hudson River Trading, as a replacement for an older generator called BETTER_ENUM.

  • Added travis.yml

    Added travis.yml

    Your CONTRIBUTING.md states that you are looking for a third-party service to run your tests on. Travis is a continous integration service that builds every commit and even pull requests for you. You can log in using your github account and add your repository. Every time you push a new commit or someone submits a pull request, travis will build the commit and notify you if it failed. You can learn more about travis here.

    This PR adds a .travis.yml so that travis knows how to run your tests. It currently tests clang 3.4 and g++ 4.8. For an example how this might look see https://travis-ci.org/UnrealQuester/better-enums/builds/68665505

    opened by UnrealQuester 28
  • Usage inside a class

    Usage inside a class

    You can do something like this:

    // Make sure it's possible to compare string correctly
    constexpr bool static_strequal_helper(const char * a, const char * b, unsigned len) {
       return (len == 0) ? true : ((*a == *b) ? static_strequal_helper(a + 1, b + 1, len - 1) : false);
    // This is the base class using CRTP for capturing the enum' class type
    // With the macro trick below, it allow auto registration even in classes of your enum, and 
    // also O(1) runtime string lookup-to-value matching
    template <typename T>
    struct CatalogEnum
         typedef T ClassType;
         static std::map<const char *, int> enumToValue; 
         static void registerField(const char * name, int value) { enumToValue[name] = value; }
         static int fromStringImpl(const char * name) { return enumToValue[name]; }
    /* This is the basic block. Because your enum derives from CatalogEnum, it has a registerField member, so it can be registered at run time (before any usage)
    Also, I've provided a basic constexpr trick to match against an enum value, but not the code 
    for complete lookup. 
    It should not be difficult to iterate over all the RegisterEnum entries at compile time to perform O(N) lookup for a fromString method. 
    Please notice that even if you enum as same value for 2 field, it'll generate two different instance of this
    template, and will still work correctly, since the pointer to _get_field_name is different */ 
    template <typename Class, int value, typename const char* (*enumName)()>
    struct RegisterEnum
          // Compile-time version
          template<size_t N>
          constexpr bool match_string(const char (&a)[N]) const { return static_strequal_helper(a, (*enumName)(), N); }
          // Run-time version
          bool match_string(const char* a) const { return strcmp(a, (*enumName)()) == 0; }
          RegisterEnum() { CatalogEnum<Class>::registerField((*enumName)(), value); }
    // Basic macro trick, it declares a static function, and uses its address as a templated differentiator
    // Then the templated object constructor takes care of calling the Catalog::registerField method to register 
    // the enum field
    #define DeclMember(A) \
           static const char *__get##A() { return #A; } \
           RegisterEnum<ClassType, A, &__get##A> __##A;
    // And some of your code:
    #define ENUM(Name, type, A, B, C) \
        struct Name : CatalogEnum<Name> { enum Type : type { A, B, C }; \
           DeclMember(A) \
           DeclMember(B) \
           DeclMember(C) \
           static Type fromString(const char * name) { return (Type)fromStringImpl(name); } \
           template <size_t N>
           static constexpr fromString(const char (&a)[N]); // Should iterate through all RegisterEnum  and call match_string(a) on them  
       [your actual code here]
    // Usage:
    struct A
          ENUM(Color, int, Blue, Red, Green); // OMG, it works!
         void exampleMethod() { Color::Type c = Color::fromString("RED"); }
    opened by X-Ryl669 20
  • Visual Studio 2015 constexpr status

    Visual Studio 2015 constexpr status

    Visual Studio 2015 added support for constexpr, but the implementation seems too buggy to get it working with Better Enums without a bunch of workarounds. Progress is in the branch vs2015-constexpr. Internal compiler errors can be seen here – search for "error" in the log.

    opened by aantron 14
  • Enum type should be default constructible

    Enum type should be default constructible

    Normal scoped enumerations are default constructible:

    enum class Fubar { One, Two, Three };
    auto myinstance = Fubar{};

    However, your ENUM macro does not yield a struct that matches these semantics:

    ENUM(Fubar, int, One, Two, Three);
    auto myinstance = Fubar{}; // compiler error on MSVC12

    The error I get is:

    error C2248: 'Fubar' : cannot access private member declared in class 'Fubar'

    These semantics are extremely important for template metaprogramming. Example test case:

    template<typename T>
    void DeserializeEnum(T& enumerator, T const& default_value = T{});

    Internally, the method above will attempt to stream in a string and map it to a proper enumerator. If the string does not map to a valid enumerator, it will instead set it to the value of default_value. This template works just fine for true scoped enumerations, but not with your struct declared by the ENUM macro.

    opened by rcdailey 13
  • Increase compiler warning levels and associated code changes

    Increase compiler warning levels and associated code changes

    Thanks for Better Enums. It's incredibly useful.

    Some projects wishing to include enum.h might be following the advice of enabling all available compiler warning flags (eg C++ Coding Standards by Herb Sutter and Andrei Alexandrescu, Item #1, "Compile cleanly at high warning levels"). Such projects currently need to either modify enum.h or use #pragm directives to disable warnings for that file.

    This PR modifies the example and test Makefile to enable all available warning flags, along with associated code changes to comply with the resulting compiler warnings. This allows enum.h to be directly used in projects without editing or #pragma directives. The test cases pass and the examples execute without error.

    opened by benalexau 12
  • Recommend magic_enum?

    Recommend magic_enum?

    See https://github.com/Neargye/magic_enum#readme.

    If someone tries both Better Enums and magic_enum, and there is a reason to prefer Better Enums, please leave a comment here.

    Otherwise, I think we should recommend magic_enum and move Better Enums toward deprecation.

    cc @Neargye

    opened by aantron 11
  • Are there guarantees on size with better enums?

    Are there guarantees on size with better enums?

    I'm in a weird situation where, because of std::vector<bool> bit packing and a need to interface with a C API I need to make my own boolean type (the other alternative being using a non-standard container, like boost::container::vector).

    Because of that C API I need a guarantee that sizeof(BETTER_ENUM(foo, char)) == sizeof(char), does Better Enums provide such a guarantee?

    Using a simple test code (below) this seems to be true, but the actual implementation is somewhere so deep among the macros it's difficult to analyze.

    Test code:

    #include <iostream>
    #include <better-enums/enum.h>
    BETTER_ENUM(mbool, char, mfalse = 0, mtrue = 1)
    int main() {
        std::cout << sizeof(mbool) << ' ' << sizeof(char) << std::endl;
        std::cout << std::boolalpha << (sizeof(mbool) == sizeof(char)) << std::endl;
        return 0;

    Edit: I'm aware that enum class mbool : char would work for this use case, but Better Enums are, well, better.

    opened by jaskij 10
  • constexpr not working in Visual Studio 2017?

    constexpr not working in Visual Studio 2017?

    Hello @aantron & co.,

    Trying to compile with BETTER_ENUM in Visual Studio 2017 produces the following error:

    E0028 expression must have a constant value attempt to access run-time storage

    The error occurs at the assignment of _value_array.

    Here are a few test cases of the compiler behavior:

        //These compile
        constexpr const int example0[] = {
        constexpr const MyEnum example1[] = {
        constexpr const int myEnumValue = MyEnum::MyEnumValue;
        constexpr const int example2[] = {
        //These array assignments all produce error E0028
        constexpr const MyEnum example3[] = {
          ((::better_enums::_eat_assign<MyEnum>)MyEnum::MyEnumValue = 0)
        constexpr const MyEnum example4[] = {
        constexpr ::better_enums::_eat_assign<MyEnum> myEat(MyEnum::MyEnumValue);
        constexpr const MyEnum example5[] = {

    This is in Visual Studio 2017 (v15.4.5), and happens using any of the ISO C++14, ISO C++17, and Latest Draft compilers.

    I know this is intended to work (apropos the recent commit to support constexpr in VS2017). What's likely to be the issue?

    ❤️ , dan

    opened by dgant 10
  • Support using better-enum as key in dictionaries and maps.

    Support using better-enum as key in dictionaries and maps.

    Thanks for better-enum. It is awesome. However I was missing a feature to use the enum values in unordered_map. I have extended it for this use case. Please review and accept my PR.

    int main()
    	Channel channel = Channel::Red;
    	std::unordered_map<Channel, int> u = {
    		{Channel::Red, 1},
    		{Channel::Blue, 3},
    	printf("Red %d\n", u[Channel::Red]);
    	printf("Blue %d\n", u[Channel::Blue]);
    	return 0;
    opened by svnscha 9
  • Fix name resolution errors

    Fix name resolution errors

    1. Global stream I/O operators were sometimes not found in my code. I didn't have enough patience to detect the exact cause of this and to reproduce the error using a small example, but this is apparently due to some complex ADL rules. I moved the operators to the enum namespace scope as I think it's more appropriate, the lookup is more reliable now. It also allowed to get rid of the hacky "traits" class.
    2. Using better_enums as a name for both global and nested namespaces is pretty error-prone as the nested one will be chosen by default, unless ::better_enums is specified explicitly. I concatenated the nested namespace names to produce a unique one and prevent the name clash.
    opened by cheparukhin 9
  • Appveyor and Travis badge

    Appveyor and Travis badge

    Now that we have ci, you might want to add the travis status image and the appveyor status badge. This way users can immediately see that you project has automated tests and feel a little more comfortable in using it. And potential contributors can be confident that their contributions are automatically tested.

    opened by UnrealQuester 9
  • How to reflect to enum with type and value strings?

    How to reflect to enum with type and value strings?

    Hi, this is a great work you’v made. But how to reflect from strings of enum value and name?

    I have,

    enum Type
       A = 1,
       B = 2

    and text content

    enum name : Type ; value: A

    How to reflect the strings into Type with A?

    I know there is no reflection in c++, but can we build that system just with help of this better-enum project?

    opened by WorstCodeWay 4
  • Compile-time name trimming and binary size

    Compile-time name trimming and binary size

    I've added better-enums to an embedded project with limited binary size. After converting a single existing enum to BETTER_ENUM the binary size increased by ~5 kB which is not acceptable for such a project. I was able to trim this to less than 1 kB by enabling the compile-time name trimming feature so it seems that the runtime code is pulling in many dependencies or generating much code.

    In such a case using the compile-time name trimming feature is definitely preferred, so I suggest to add a small note about that to the documentation for other users.

    opened by Christian-Sander 0
  • enums stops being enums

    enums stops being enums

    There doesn't really seem to be much gained from wrapping everything in a class, but perhaps I'm missing something? For one it's not possible to forward declare the enum any longer since it's nested. If you try to retrofit it into an existing code base you run into a myriad of problems because suddenly your enums aren't really enums any longer. Enums are strongly typed from the get go, so it would seem most if not all the functionality could be had from generating function overloads anyway?

    opened by Sairony 1
  • Compiling example code: 5-map.cc fail

    Compiling example code: 5-map.cc fail


    This is a wonderful library I am looking for. However, when I am trying to compile the example code from the master branch, It fails with an error message:

    5-map.cc:44:1: error: body of ‘constexpr’ function ‘constexpr const char* describe(Channel)’ not a return-statement
       44 | }
          | ^
    make: *** [Makefile:20: 5-map.exe] Error 1

    The g++ version I am using:

    g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
    Copyright (C) 2019 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO



    opened by YuxinxinChen 1
  • Use in a packed struct

    Use in a packed struct

    BETTER_ENUM(address_t, uint8_t, one = 0x01, two = 0x02);
    struct query_t {
        address_t address;
    } __attribute__((packed, aligned(1)));

    Gives a warning: ignoring packed attribute because of unpacked non-POD field 'address_t query_t::address'

    opened by vervaekejonathan 1
  • Static functions for enum types

    Static functions for enum types

    I'm trying to emulate java's ability to add a static function to an enum class but using better enums.

    `namespace playground { BETTER_ENUM(Vegetable, int, potato, brocolli, carrot )

    std::string getColor(Vegetable toGet) {
        switch (toGet) {
            case Vegetable::potato:
                return "brown";
            case Vegetable::brocolli:
                return "green";
            case Vegetable::carrot:
                return "orange";
                return "unknown";


    I'd like to be able to simply call Vegetable::getColor(Vegetable::carrot), for example. Is there any way to add functions to the class generated by better enums?

    opened by reddigfabian 1
  • 0.11.3(Oct 19, 2020)


    Bugs fixed

    • -Wold-style-cast on Clang (#74, Felipe Lema).
    • Don't trigger compiler bug with -Wattributes on GCC ≥ 7 (#79, CJ Smith).
    • Missing BETTER_ENUMS_IGNORE_ATTRIBUTES_* definitions on Clang (#81, Jan-Gerd Tenberge).
    Source code(tar.gz)
    Source code(zip)
  • 0.11.2(Apr 2, 2019)


    • Enable constexpr support on clang-cl (#26, Zsolt Parragi).
    • Enable constexpr support on VS 2017 (#47, Zsolt Parragi).
    • _to_index, _from_index, and related functions (#59, Piotr Kosek).
    • Specialize maps for descriptions of type wchar_t* (#44, @codercheny).

    Bugs fixed

    • Move stream I/O operators out of the global namespace (#22, Alex Cheparukhin).
    • Internal namespaces used by Better Enums cause name clashes (#22, Alex Cheparukhin).
    • Unused function warnings on comparison operators (#27, Alex Cheparukhin).
    • Unused variables with names cause warnings on MSVC (#41, Anuradha Dissanayake).
    • VS 2015 warns when not using enum class (#41, Anuradha Dissanayake).
    • Docs: note strongly that warning C4062 has to be enabled on MSVC for exhaustiveness checking (#49).
    • Identifiers that begin with an underscore followed by a capital letter are reserved (#61, Felix Dombek).
    • Internal values array initialization not accepted as constexpr by VS 2017 (#53, @D4koon).


    • Syntax-highlight the code in the README (#67, Wojciech Bartnik).
    • Remove tabs that have crept into enum.h (#72, @Xeverous).
    Source code(tar.gz)
    Source code(zip)
  • 0.11.1(Mar 14, 2016)

    • Removed double underscores in internal names (by Mikhail Ovchinnikov).
    • Fixed some warnings (some by Mitsutaka Takeda).
    • Various build, testing, and documentation fixes.
    Source code(tar.gz)
    Source code(zip)
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