C++ 预处理器 __VA_ARGS__ 参数数量 [英] C++ preprocessor __VA_ARGS__ number of arguments

问题描述

我在网上找不到答案的简单问题.在可变参数宏中，如何找到参数的数量?我对 boost 预处理器没问题，如果它有解决方案的话.

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.

如果它有所作为，我正在尝试将可变数量的宏参数转换为增强预处理器序列、列表或数组，以便进一步重新处理.

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

这实际上依赖于编译器，不受任何标准支持.

This is actually compiler dependent, and not supported by any standard.

然而，这里有一个 宏实现 计数:

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

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