C++ 宏扩展(__VA_ARGS__项名称和值）

c++ macro expansion(__VA_ARGS__ item name and value)

本文关键字：ARGS 扩展 VA C++      更新时间：2023-10-16

下面伪代码的功能有什么技巧吗？ 感谢。

template <typename... T1, typename... T2>
void fake_fold((T1 t1, T2 t2)...) {
(std::make_pair(t1, t2)), ...; // std::pair<std::string, T2>, T1 type is always sd::string
}
#define FAKE_MACRO(a, b, c) fake_fold(???)
void main()
{
int var1;
std::string var2;
double var3;
FAKE_MACRO(var1, var2, var3);
/* macro expansion then pass to fake_fold:
fake_fold("var1", var1, "var2", var2, "var3", var3);
*/
/* fold expression expansion:
std::make_pair("var1", var1), std::make_pair("var2", var2), std::make_pair("var3", var3),
*/
}

不久 使用FAKE_MACRO(var1, var2, var3);我想获取扩展代码

std::make_pair("var1", var1), std::make_pair("var2", var2), std::make_pair("var3", var3)

var0 ...瓦恩

from 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 X(a) std::make_pair(#a, a)
#define FAKE_MACRO(...) fake_fold(APPLYXn(__VA_ARGS__))    
int main()
{
int var1 = 42;
std::string var2 = "toto";
double var3 = 5.1;
FAKE_MACRO(var1, var2, var3);
}

演示

相关文章：