预处理器：将字符串连接到__VA_ARGS__中的每个参数

时间：2017-06-11 00:19:47

标签： c macros c-preprocessor

我想在可变参数宏中为每个元素附加一个字符串化的宏参数。我想我知道我需要什么，但我还没有想出一个有效的解决方案。鉴于可变宏，如：

#define FIELD_DECLARATION(NAME, OTHER_FIELD, ...)

FIELD_DECLARATION(First, Thing)
FIELD_DECLARATION(Second, Thing, Thing, Nothing)

我想生成：

field_First = {ThingArg};
field_Second = {ThingArg, ThingArg, NothingArg};

我想我需要的是递归地继续扩展__VA_ARGS__直到它没有元素，并在进行扩展时附加"Arg"。最后，将结果传递给另一个可变参数宏，该宏生成以逗号分隔的参数列表。

我已经尝试了这个，这不会起作用（也不是我所描述的）：

#define UNPACK_VA_1(A1) A1 ## Arg
#define UNPACK_VA_2(A1, A2) UNPACK_VA_1(A1), UNPACK_VA_1(A2)
#define UNPACK_VA_3(A1, A2, A3) UNPACK_VA_2(A1, A2), UNPACK_VA_1(A3)
#define UNPACK_VA_4(A1, A2, A3, A4) UNPACK_VA_2(A1, A2), UNPACK_VA_2(A3, A4)
#define UNPACK_VA(...) UNPACK_VA_4(__VA_ARGS__)

#define FOO(x, y, ...) UNPACK_VA(__VA_ARGS__)
FOO(One, Two, Three, Four, Five, Six)

虽然这有点奏效，但我无法提出可扩展的解决方案。如果有人可以发光，那就太好了。

2 个答案:

答案 0 :(得分：7)

这是一种可扩展的方法。首先，一些通用实用程序宏：

#define EVAL(...) __VA_ARGS__
#define VARCOUNT(...) \
   EVAL(VARCOUNT_I(__VA_ARGS__,9,8,7,6,5,4,3,2,1,))
#define VARCOUNT_I(_,_9,_8,_7,_6,_5,_4,_3,_2,X_,...) X_
#define GLUE(X,Y) GLUE_I(X,Y)
#define GLUE_I(X,Y) X##Y
#define FIRST(...) EVAL(FIRST_I(__VA_ARGS__,))
#define FIRST_I(X,...) X
#define TUPLE_TAIL(...) EVAL(TUPLE_TAIL_I(__VA_ARGS__))
#define TUPLE_TAIL_I(X,...) (__VA_ARGS__)

#define TRANSFORM(NAME_, ARGS_) (GLUE(TRANSFORM_,VARCOUNT ARGS_)(NAME_, ARGS_))
#define TRANSFORM_1(NAME_, ARGS_) NAME_ ARGS_
#define TRANSFORM_2(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_1(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_3(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_2(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_4(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_3(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_5(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_4(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_6(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_5(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_7(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_6(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_8(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_7(NAME_,TUPLE_TAIL ARGS_)
#define TRANSFORM_9(NAME_, ARGS_) NAME_(FIRST ARGS_),TRANSFORM_8(NAME_,TUPLE_TAIL ARGS_)

在语义上，VARCOUNT计算参数; GLUE是典型的间接贴纸; FIRST提取第一个参数; EVAL扩展为其参数（意图评估），TUPLE_TAIL返回元组的尾部（即，它丢弃第一个参数）。

TRANSFORM这是主要的想法; TRANSFORM(FOO,(X,Y,Z))将元组(X,Y,Z)带到(FOO(X),FOO(Y),FOO(Z))。

这就是这里的特殊用途代码：

#define Z_ARG(X) GLUE(X,Arg)
#define MAKE_INITIALIZER(...) { __VA_ARGS__ }
#define FIELD_DECLARATION(FNAME_, ...) \
   GLUE(field_, FNAME_) = EVAL(MAKE_INITIALIZER TRANSFORM(Z_ARG, (__VA_ARGS__)));

鉴于上述情况，这应该是可读的，但只是解释...... Z_ARG粘贴Arg到项目; MAKE_INITIALIZER将预处理器元组转换为初始化列表;而FIELD_DECLARATION是你的宏。请注意EVAL包装MAKE_INITIALIZER /转换后的元组，以便实际调用该宏。

注意：将EVAL移至顶部并在更多位置使用它，这样也可以在MSVC中使用。

Demonstration, original code

Demonstration, current code

答案 1 :(得分：0)

我已经在Visual Studio C ++上测试了上面的代码，存在一些问题，并且编译器显示错误。 不需要一些专门用于 VA_ARGS 的小游戏，而且在某些地方，我们必须使用 VA_ARGS 和。 。代替了正确的代码“ Args ”，并且扩展到60个输入项是：

#ifndef __MACROS__
#define __MACROS__
#define EVAL(...) __VA_ARGS__
#define VARCOUNT(...) \
   EVAL(VARCOUNT_I(__VA_ARGS__,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,))
#define VARCOUNT_I(_,_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,X_,...) X_
#define GLUE(X,Y) GLUE_I(X,Y)
#define GLUE_I(X,Y) X##Y
#define FIRST(...) EVAL(FIRST_I(__VA_ARGS__,))
#define FIRST_I(X,Args) X
#define TUPLE_TAIL(...) EVAL(TUPLE_TAIL_I(__VA_ARGS__))
#define TUPLE_TAIL_I(X,...) __VA_ARGS__

#define TRANSFORM(NAME_, ...) GLUE(TRANSFORM_,VARCOUNT(__VA_ARGS__))(NAME_, __VA_ARGS__)
#define TRANSFORM_1(NAME_, ARGS_) NAME_ (ARGS_)
#define TRANSFORM_2(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_1(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_3(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_2(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_4(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_3(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_5(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_4(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_6(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_5(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_7(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_6(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_8(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_7(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_9(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_8(NAME_,TUPLE_TAIL( ARGS_))

#define TRANSFORM_10(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_9(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_11(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_10(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_12(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_11(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_13(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_12(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_14(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_13(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_15(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_14(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_16(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_15(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_17(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_16(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_18(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_17(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_19(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_18(NAME_,TUPLE_TAIL( ARGS_))

#define TRANSFORM_20(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_19(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_21(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_20(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_22(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_21(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_23(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_22(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_24(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_23(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_25(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_24(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_26(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_25(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_27(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_26(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_28(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_27(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_29(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_28(NAME_,TUPLE_TAIL( ARGS_))

#define TRANSFORM_30(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_29(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_31(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_30(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_32(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_31(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_33(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_32(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_34(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_33(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_35(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_34(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_36(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_35(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_37(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_36(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_38(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_37(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_39(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_38(NAME_,TUPLE_TAIL( ARGS_))

#define TRANSFORM_40(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_39(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_41(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_40(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_42(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_41(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_43(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_42(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_44(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_43(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_45(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_44(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_46(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_45(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_47(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_46(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_48(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_47(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_49(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_48(NAME_,TUPLE_TAIL( ARGS_))

#define TRANSFORM_50(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_49(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_51(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_50(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_52(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_51(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_53(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_52(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_54(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_53(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_55(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_54(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_56(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_55(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_57(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_56(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_58(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_57(NAME_,TUPLE_TAIL( ARGS_))
#define TRANSFORM_59(NAME_, ARGS_) NAME_(FIRST (ARGS_)) TRANSFORM_58(NAME_,TUPLE_TAIL( ARGS_))
#endif
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