C ++ preprocessor __VA_ARGS__的参数的数目 [英] C++ preprocessor __VA_ARGS__ number of arguments
问题描述
简单的问题,对此我无法在网络上找到答案。在可变参数宏的说法,如何找到参数的数量?我还好用升压preprocessor,如果有解决方案。
Simple question for which I could not find answer on the net. In variadic argument macros, how to find the number of arguments? I am okay with boost preprocessor, if it has the solution.
如果它的确与众不同,我想转换成可变数量的宏参数,以提高preprocessor序列,列表或数组用于进一步加工处理。
If it makes a difference, I am trying to convert variable number of macro arguments to boost preprocessor sequence, list, or array for further reprocessing.
推荐答案
这其实是编译器相关的,而不是由任何标准的支持。
This is actually compiler dependent, and not supported by any standard.
在这里,但是你有一个<一个href=\"http://groups.google.com/group/comp.std.c/browse_thread/thread/77ee8c8f92e4a3fb/346fc464319b1ee5?pli=1\">macro实施,做的次数:
Here however you have a macro implementation that does the count:
#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
/* Some test cases */
PP_NARG(A) -> 1
PP_NARG(A,B) -> 2
PP_NARG(A,B,C) -> 3
PP_NARG(A,B,C,D) -> 4
PP_NARG(A,B,C,D,E) -> 5
PP_NARG(1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3,4,5,6,7,8,9,0,
1,2,3) -> 63
这篇关于C ++ preprocessor __VA_ARGS__的参数的数目的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!