在可变参数宏中指向每个宏的每个参数前缀 [英] Prefix each parameter in a variadic macro that points to another macro

问题描述

让我们假设我有这些以ATTRIB_

Let's assume that I have these macros that are prefixed with ATTRIB_

#define ATTRIB_A "a"
#define ATTRIB_B "b"
#define ATTRIB_C "c"

我希望能够使用可变参数宏来解压缩每个给定参数，然后在其前加上ATTRIB_前缀以获得属性宏的全名，以扩展该宏:

I would like to be able to use a variadic macro that unpacks each given parameter then prefixes it with ATTRIB_ to obtain the full name of an attribute macro in order to expand that macro:

#define ATTRIBS(...) CONFUSED_HERE(##__VA_ARGS__)

将用作:

const char * a = ATTRIBS(A, B, C);

结果将等于:

const char * a = "a" "b" "c";

就像( 除外)一样使用:

As if used like (except shorter):

ATTRIBS(ATTRIB_A, ATTRIB_B, ATTRIB_C);

请注意，这不是此宏的实际用法.我很好奇如何将前缀应用于可变参数宏的每个参数以访问/扩展另一个宏.

Please note that this is not the actual use for this macro. I'm rather curious on how can a prefix be applied to each parameter of a variadic macro in order to access/expand another macro.

我不关心可移植性，只要它适用于最新的MinGW/GCC编译器即可.如果它们带有一些我不知道的扩展名.

I am not concerned with portability as long as it works on recent MinGW/GCC compilers. In case they come with some extension that I'm not aware of.

推荐答案

来自 foreach-macro-on-macros-arguments

#define PP_NARG(...)    PP_NARG_(__VA_ARGS__,PP_RSEQ_N())
#define PP_NARG_(...)   PP_ARG_N(__VA_ARGS__)

#define 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 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


/* need extra level to force extra eval */
#define Paste(a,b) a ## b
#define XPASTE(a,b) Paste(a,b)


/* APPLYXn variadic X-Macro by M Joshua Ryan      */
/* Free for all uses. Don't be a jerk.            */
/* I got bored after typing 15 of these.          */
/* You could keep going upto 64 (PPNARG's limit). */
#define APPLYX1(a)           X(a)
#define APPLYX2(a,b)         X(a) X(b)
#define APPLYX3(a,b,c)       X(a) X(b) X(c)
#define APPLYX4(a,b,c,d)     X(a) X(b) X(c) X(d)
#define APPLYX5(a,b,c,d,e)   X(a) X(b) X(c) X(d) X(e)
#define APPLYX6(a,b,c,d,e,f) X(a) X(b) X(c) X(d) X(e) X(f)
#define APPLYX7(a,b,c,d,e,f,g) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g)
#define APPLYX8(a,b,c,d,e,f,g,h) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h)
#define APPLYX9(a,b,c,d,e,f,g,h,i) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i)
#define APPLYX10(a,b,c,d,e,f,g,h,i,j) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j)
#define APPLYX11(a,b,c,d,e,f,g,h,i,j,k) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j) X(k)
#define APPLYX12(a,b,c,d,e,f,g,h,i,j,k,l) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j) X(k) X(l)
#define APPLYX13(a,b,c,d,e,f,g,h,i,j,k,l,m) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j) X(k) X(l) X(m)
#define APPLYX14(a,b,c,d,e,f,g,h,i,j,k,l,m,n) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j) X(k) X(l) X(m) X(n)
#define APPLYX15(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o) \
    X(a) X(b) X(c) X(d) X(e) X(f) X(g) X(h) X(i) X(j) X(k) X(l) X(m) X(n) X(o)
#define APPLYX_(M, ...) M(__VA_ARGS__)
#define APPLYXn(...) APPLYX_(XPASTE(APPLYX, PP_NARG(__VA_ARGS__)), __VA_ARGS__)


#define ATTRIB_A "a"
#define ATTRIB_B "b"
#define ATTRIB_C "c"


#define X(a) XPASTE(ATTRIB_, a)

#define ATTRIBS(...) APPLYXn(__VA_ARGS__)

int main()
{
    const char * a = ATTRIBS(A, B, C);

    std::cout << a << std::endl;
}

演示

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