根据OP的要求，这里有一个基于Boost preproessor和Variadic Macros的丑陋宏解决方案的精简版本。
它允许类似枚举元素语法的简单列表，并为特定元素设置值，以便
XXX_ENUM(foo,(a,b,(c,42)));
扩大到
enum foo {
a,
b,
c=42
};
与必要的函数一起输出并做一些转换。这个宏已经存在了很长时间，我不完全确定这是最有效的方式，或者它是一种一致的方式，但它一直以来都在工作
完整的代码可以在Ideone和Coliru中看到。
它的巨大丑陋在上面;如果我知道怎么做，我会把它放在剧透后面保护你的眼睛，但markdown不喜欢我。
库(合并在一个头文件中)
#include <boost/preprocessor.hpp>
#include <string>
#include <unordered_map>
namespace xxx
{
template<class T>
struct enum_cast_adl_helper { };
template<class E>
E enum_cast( const std::string& s )
{
return do_enum_cast(s,enum_cast_adl_helper<E>());
}
template<class E>
E enum_cast( const char* cs )
{
std::string s(cs);
return enum_cast<E>(s);
}
} // namespace xxx
#define XXX_PP_ARG_N( \
_1, _2, _3, _4, _5, _6, _7, _8, _9,_10, \
_11,_12,_13,_14,_15,_16,_17,_18,_19,_20, \
_21,_22,_23,_24,_25,_26,_27,_28,_29,_30, \
_31,_32,_33,_34,_35,_36,_37,_38,_39,_40, \
_41,_42,_43,_44,_45,_46,_47,_48,_49,_50, \
_51,_52,_53,_54,_55,_56,_57,_58,_59,_60, \
_61,_62,_63,N,...) N
#define XXX_PP_RSEQ_N() \
63,62,61,60, \
59,58,57,56,55,54,53,52,51,50, \
49,48,47,46,45,44,43,42,41,40, \
39,38,37,36,35,34,33,32,31,30, \
29,28,27,26,25,24,23,22,21,20, \
19,18,17,16,15,14,13,12,11,10, \
9,8,7,6,5,4,3,2,1,0
#define XXX_PP_NARG_(...) XXX_PP_ARG_N(__VA_ARGS__)
#define XXX_PP_NARG(...) XXX_PP_NARG_(__VA_ARGS__,XXX_PP_RSEQ_N())
#define XXX_TUPLE_SIZE_INTERNAL(TUPLE) XXX_PP_NARG TUPLE
#define XXX_TUPLE_CHOICE(i) \
BOOST_PP_APPLY( \
BOOST_PP_TUPLE_ELEM( \
25, i, ( \
(0), (1), (2), (3), (4), (5), (6), (7), (8), \
(9), (10), (11), (12), (13), (14), (15), (16), \
(17), (18), (19), (20), (21), (22), (23), (24) \
) ) )
#define BOOST_PP_BOOL_00 BOOST_PP_BOOL_0
#define BOOST_PP_BOOL_01 BOOST_PP_BOOL_1
#define BOOST_PP_BOOL_02 BOOST_PP_BOOL_2
#define BOOST_PP_BOOL_03 BOOST_PP_BOOL_3
#define BOOST_PP_BOOL_04 BOOST_PP_BOOL_4
#define BOOST_PP_BOOL_05 BOOST_PP_BOOL_5
#define BOOST_PP_BOOL_06 BOOST_PP_BOOL_6
#define BOOST_PP_BOOL_07 BOOST_PP_BOOL_7
#define BOOST_PP_BOOL_08 BOOST_PP_BOOL_8
#define BOOST_PP_BOOL_09 BOOST_PP_BOOL_9
#define BOOST_PP_BOOL_010 BOOST_PP_BOOL_10
#define BOOST_PP_BOOL_011 BOOST_PP_BOOL_11
#define BOOST_PP_BOOL_012 BOOST_PP_BOOL_12
#define BOOST_PP_BOOL_013 BOOST_PP_BOOL_13
#define BOOST_PP_BOOL_014 BOOST_PP_BOOL_14
#define BOOST_PP_BOOL_015 BOOST_PP_BOOL_15
#define BOOST_PP_BOOL_016 BOOST_PP_BOOL_16
#define BOOST_PP_BOOL_017 BOOST_PP_BOOL_17
#define BOOST_PP_BOOL_018 BOOST_PP_BOOL_18
#define BOOST_PP_BOOL_019 BOOST_PP_BOOL_19
#define BOOST_PP_BOOL_020 BOOST_PP_BOOL_20
#define BOOST_PP_BOOL_021 BOOST_PP_BOOL_21
#define BOOST_PP_BOOL_022 BOOST_PP_BOOL_22
#define BOOST_PP_BOOL_023 BOOST_PP_BOOL_23
#define BOOST_PP_BOOL_024 BOOST_PP_BOOL_24
#define BOOST_PP_BOOL_025 BOOST_PP_BOOL_25
#define BOOST_PP_BOOL_026 BOOST_PP_BOOL_26
#define BOOST_PP_BOOL_027 BOOST_PP_BOOL_27
#define BOOST_PP_BOOL_028 BOOST_PP_BOOL_28
#define BOOST_PP_BOOL_029 BOOST_PP_BOOL_29
#define BOOST_PP_BOOL_030 BOOST_PP_BOOL_30
#define BOOST_PP_BOOL_031 BOOST_PP_BOOL_31
#define BOOST_PP_BOOL_032 BOOST_PP_BOOL_32
#define BOOST_PP_BOOL_033 BOOST_PP_BOOL_33
#define BOOST_PP_BOOL_034 BOOST_PP_BOOL_34
#define BOOST_PP_BOOL_035 BOOST_PP_BOOL_35
#define BOOST_PP_BOOL_036 BOOST_PP_BOOL_36
#define BOOST_PP_BOOL_037 BOOST_PP_BOOL_37
#define BOOST_PP_BOOL_038 BOOST_PP_BOOL_38
#define BOOST_PP_BOOL_039 BOOST_PP_BOOL_39
#define BOOST_PP_BOOL_040 BOOST_PP_BOOL_40
#define BOOST_PP_BOOL_041 BOOST_PP_BOOL_41
#define BOOST_PP_BOOL_042 BOOST_PP_BOOL_42
#define BOOST_PP_BOOL_043 BOOST_PP_BOOL_43
#define BOOST_PP_BOOL_044 BOOST_PP_BOOL_44
#define BOOST_PP_BOOL_045 BOOST_PP_BOOL_45
#define BOOST_PP_BOOL_046 BOOST_PP_BOOL_46
#define BOOST_PP_BOOL_047 BOOST_PP_BOOL_47
#define BOOST_PP_BOOL_048 BOOST_PP_BOOL_48
#define BOOST_PP_BOOL_049 BOOST_PP_BOOL_49
#define BOOST_PP_BOOL_050 BOOST_PP_BOOL_50
#define BOOST_PP_BOOL_051 BOOST_PP_BOOL_51
#define BOOST_PP_BOOL_052 BOOST_PP_BOOL_52
#define BOOST_PP_BOOL_053 BOOST_PP_BOOL_53
#define BOOST_PP_BOOL_054 BOOST_PP_BOOL_54
#define BOOST_PP_BOOL_055 BOOST_PP_BOOL_55
#define BOOST_PP_BOOL_056 BOOST_PP_BOOL_56
#define BOOST_PP_BOOL_057 BOOST_PP_BOOL_57
#define BOOST_PP_BOOL_058 BOOST_PP_BOOL_58
#define BOOST_PP_BOOL_059 BOOST_PP_BOOL_59
#define BOOST_PP_BOOL_060 BOOST_PP_BOOL_60
#define BOOST_PP_BOOL_061 BOOST_PP_BOOL_61
#define BOOST_PP_BOOL_062 BOOST_PP_BOOL_62
#define BOOST_PP_BOOL_063 BOOST_PP_BOOL_63
#define BOOST_PP_DEC_00 BOOST_PP_DEC_0
#define BOOST_PP_DEC_01 BOOST_PP_DEC_1
#define BOOST_PP_DEC_02 BOOST_PP_DEC_2
#define BOOST_PP_DEC_03 BOOST_PP_DEC_3
#define BOOST_PP_DEC_04 BOOST_PP_DEC_4
#define BOOST_PP_DEC_05 BOOST_PP_DEC_5
#define BOOST_PP_DEC_06 BOOST_PP_DEC_6
#define BOOST_PP_DEC_07 BOOST_PP_DEC_7
#define BOOST_PP_DEC_08 BOOST_PP_DEC_8
#define BOOST_PP_DEC_09 BOOST_PP_DEC_9
#define BOOST_PP_DEC_010 BOOST_PP_DEC_10
#define BOOST_PP_DEC_011 BOOST_PP_DEC_11
#define BOOST_PP_DEC_012 BOOST_PP_DEC_12
#define BOOST_PP_DEC_013 BOOST_PP_DEC_13
#define BOOST_PP_DEC_014 BOOST_PP_DEC_14
#define BOOST_PP_DEC_015 BOOST_PP_DEC_15
#define BOOST_PP_DEC_016 BOOST_PP_DEC_16
#define BOOST_PP_DEC_017 BOOST_PP_DEC_17
#define BOOST_PP_DEC_018 BOOST_PP_DEC_18
#define BOOST_PP_DEC_019 BOOST_PP_DEC_19
#define BOOST_PP_DEC_020 BOOST_PP_DEC_20
#define BOOST_PP_DEC_021 BOOST_PP_DEC_21
#define BOOST_PP_DEC_022 BOOST_PP_DEC_22
#define BOOST_PP_DEC_023 BOOST_PP_DEC_23
#define BOOST_PP_DEC_024 BOOST_PP_DEC_24
#define BOOST_PP_DEC_025 BOOST_PP_DEC_25
#define BOOST_PP_DEC_026 BOOST_PP_DEC_26
#define BOOST_PP_DEC_027 BOOST_PP_DEC_27
#define BOOST_PP_DEC_028 BOOST_PP_DEC_28
#define BOOST_PP_DEC_029 BOOST_PP_DEC_29
#define BOOST_PP_DEC_030 BOOST_PP_DEC_30
#define BOOST_PP_DEC_031 BOOST_PP_DEC_31
#define BOOST_PP_DEC_032 BOOST_PP_DEC_32
#define BOOST_PP_DEC_033 BOOST_PP_DEC_33
#define BOOST_PP_DEC_034 BOOST_PP_DEC_34
#define BOOST_PP_DEC_035 BOOST_PP_DEC_35
#define BOOST_PP_DEC_036 BOOST_PP_DEC_36
#define BOOST_PP_DEC_037 BOOST_PP_DEC_37
#define BOOST_PP_DEC_038 BOOST_PP_DEC_38
#define BOOST_PP_DEC_039 BOOST_PP_DEC_39
#define BOOST_PP_DEC_040 BOOST_PP_DEC_40
#define BOOST_PP_DEC_041 BOOST_PP_DEC_41
#define BOOST_PP_DEC_042 BOOST_PP_DEC_42
#define BOOST_PP_DEC_043 BOOST_PP_DEC_43
#define BOOST_PP_DEC_044 BOOST_PP_DEC_44
#define BOOST_PP_DEC_045 BOOST_PP_DEC_45
#define BOOST_PP_DEC_046 BOOST_PP_DEC_46
#define BOOST_PP_DEC_047 BOOST_PP_DEC_47
#define BOOST_PP_DEC_048 BOOST_PP_DEC_48
#define BOOST_PP_DEC_049 BOOST_PP_DEC_49
#define BOOST_PP_DEC_050 BOOST_PP_DEC_50
#define BOOST_PP_DEC_051 BOOST_PP_DEC_51
#define BOOST_PP_DEC_052 BOOST_PP_DEC_52
#define BOOST_PP_DEC_053 BOOST_PP_DEC_53
#define BOOST_PP_DEC_054 BOOST_PP_DEC_54
#define BOOST_PP_DEC_055 BOOST_PP_DEC_55
#define BOOST_PP_DEC_056 BOOST_PP_DEC_56
#define BOOST_PP_DEC_057 BOOST_PP_DEC_57
#define BOOST_PP_DEC_058 BOOST_PP_DEC_58
#define BOOST_PP_DEC_059 BOOST_PP_DEC_59
#define BOOST_PP_DEC_060 BOOST_PP_DEC_60
#define BOOST_PP_DEC_061 BOOST_PP_DEC_61
#define BOOST_PP_DEC_062 BOOST_PP_DEC_62
#define BOOST_PP_DEC_063 BOOST_PP_DEC_63
#define XXX_TO_NUMx(x) 0 ## x
#define XXX_TO_NUM(x) BOOST_PP_ADD(0,XXX_TO_NUMx(x))
#define XXX_STRINGIZEX(x) # x
#define XXX_VSTRINGIZE_SINGLE(a,b,x) XXX_STRINGIZE(x)
#define XXX_VSTRINGIZE_TUPLE(tpl) XXX_TUPLE_FOR_EACH(XXX_VSTRINGIZE_SINGLE,,tpl)
#define XXX_TUPLE_SIZE(TUPLE) XXX_TO_NUM(XXX_TUPLE_CHOICE(XXX_TUPLE_SIZE_INTERNAL(TUPLE)))
#define XXX_TUPLE_FOR_EACH(MACRO,DATA,TUPLE) BOOST_PP_LIST_FOR_EACH(MACRO,DATA,BOOST_PP_TUPLE_TO_LIST(XXX_TUPLE_SIZE(TUPLE),TUPLE))
#define XXX_STRINGIZE(x) XXX_STRINGIZEX(x)
#define XXX_VSTRINGIZE(...) XXX_VSTRINGIZE_TUPLE((__VA_ARGS__))
#define XXX_CAST_TO_VOID_ELEMENT(r,data,elem) (void)(elem);
#define XXX_CAST_TO_VOID_INTERNAL(TUPLE) XXX_TUPLE_FOR_EACH(XXX_CAST_TO_VOID_ELEMENT,,TUPLE)
#define XXX_CAST_TO_VOID(...) XXX_CAST_TO_VOID_INTERNAL((__VA_ARGS__))
#define XXX_ENUM_EXTRACT_SP(en) BOOST_PP_TUPLE_ELEM(XXX_TUPLE_SIZE(en),0,en) = BOOST_PP_TUPLE_ELEM(XXX_TUPLE_SIZE(en),1,en)
#define XXX_ENUM_ELEMENT(r,data,elem) BOOST_PP_IF( XXX_TUPLE_SIZE(elem), XXX_ENUM_EXTRACT_SP(elem), elem) ,
#define XXX_ENUM_EXTRACT_ELEMENT(en) BOOST_PP_TUPLE_ELEM(XXX_TUPLE_SIZE(en),0,en)
#define XXX_ENUM_CASE_ELEMENT(en) BOOST_PP_IF( XXX_TUPLE_SIZE(en), XXX_ENUM_EXTRACT_ELEMENT(en), en )
#define XXX_ENUM_CASE(r,data,elem) case data :: XXX_ENUM_CASE_ELEMENT(elem) : return #data "::" XXX_STRINGIZE(XXX_ENUM_CASE_ELEMENT(elem));
#define XXX_ENUM_IFELSE(r,data,elem) else if( en == data :: XXX_ENUM_CASE_ELEMENT(elem)) { return #data "::" XXX_STRINGIZE(XXX_ENUM_CASE_ELEMENT(elem)); }
#define XXX_ENUM_CASTLIST(r,data,elem) { XXX_STRINGIZE(XXX_ENUM_CASE_ELEMENT(elem)), data :: XXX_ENUM_CASE_ELEMENT(elem) },
#define XXX_ENUM_QUALIFIED_CASTLIST(r,data,elem) { #data "::" XXX_STRINGIZE(XXX_ENUM_CASE_ELEMENT(elem)), data :: XXX_ENUM_CASE_ELEMENT(elem) },
#define XXX_ENUM_INTERNAL(TYPE,NAME,TUPLE) \
enum TYPE \
{ \
XXX_TUPLE_FOR_EACH(XXX_ENUM_ELEMENT,,TUPLE) \
BOOST_PP_CAT(last_enum_,NAME) \
}; \
\
inline \
const char* to_string( NAME en ) \
{ \
if(false) \
{ \
} \
XXX_TUPLE_FOR_EACH(XXX_ENUM_IFELSE,NAME,TUPLE) \
else if( en == NAME :: BOOST_PP_CAT(last_enum_,NAME) ) \
{ \
return XXX_VSTRINGIZE(NAME,::,BOOST_PP_CAT(last_enum_,NAME)); \
} \
else \
{ \
return "Invalid enum value specified for " # NAME; \
} \
} \
\
inline \
std::ostream& operator<<( std::ostream& os, const NAME& en ) \
{ \
os << to_string(en); \
return os; \
} \
\
inline \
NAME do_enum_cast( const std::string& s, const ::xxx::enum_cast_adl_helper<NAME>& ) \
{ \
static const std::unordered_map<std::string,NAME> map = \
{ \
XXX_TUPLE_FOR_EACH(XXX_ENUM_CASTLIST,NAME,TUPLE) \
XXX_TUPLE_FOR_EACH(XXX_ENUM_QUALIFIED_CASTLIST,NAME,TUPLE) \
}; \
\
auto cit = map.find(s); \
if( cit == map.end() ) \
{ \
throw std::runtime_error("Invalid value to cast to enum"); \
} \
return cit->second; \
}
#define XXX_ENUM(NAME,TUPLE) XXX_ENUM_INTERNAL(NAME,NAME,TUPLE)
#define XXX_ENUM_CLASS(NAME,TUPLE) XXX_ENUM_INTERNAL(class NAME,NAME,TUPLE)
#define XXX_ENUM_CLASS_TYPE(NAME,TYPE,TUPLE) XXX_ENUM_INTERNAL(class NAME : TYPE,NAME,TUPLE)
#define XXX_ENUM_TYPE(NAME,TYPE,TUPLE) XXX_ENUM_INTERNAL(NAME : TYPE,NAME,TUPLE)
使用
#include "xxx_enum.h" // the above lib
#include <iostream>
XXX_ENUM(foo,(a,b,(c,42)));
int main()
{
std::cout << "foo::a = " << foo::a <<'\n';
std::cout << "(int)foo::c = " << (int)foo::c <<'\n';
std::cout << "to_string(foo::b) = " << to_string(foo::b) <<'\n';
std::cout << "xxx::enum_cast<foo>(\"b\") = " << xxx::enum_cast<foo>("b") <<'\n';
}
编译(在main.cpp中复制粘贴头文件)
> g++ --version | sed 1q
g++ (GCC) 4.9.2
> g++ -std=c++14 -pedantic -Wall -Wextra main.cpp
main.cpp:268:31: warning: extra ';' [-Wpedantic]
XXX_ENUM(foo,(a,b,(c,42)));
^
输出
foo::a = foo::a
(int)foo::c = 42
to_string(foo::b) = foo::b
xxx::enum_cast<foo>("b") = foo::b
