在指向另一个宏的可变参数宏中为每个参数添加前缀
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【中文标题】在指向另一个宏的可变参数宏中为每个参数添加前缀【英文标题】:Prefix each parameter in a variadic macro that points to another macro 【发布时间】:2017-04-03 20:58:43 【问题描述】:假设我有这些以ATTRIB_
为前缀的宏
#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,然后在其前面加上 ATTRIB_
前缀以获得属性宏的全名,以便扩展该宏:
#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";
就像使用一样(除了更短):
ATTRIBS(ATTRIB_A, ATTRIB_B, ATTRIB_C);
请注意,这不是该宏的实际用途。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。
我不关心可移植性,只要它适用于最近的 MinGW/GCC 编译器。以防它们带有一些我不知道的扩展。
【问题讨论】:
【参考方案1】: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;
Demo
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