本文介绍了可变参数`ELEM`宏观供C使用的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想知道如果theres普遍使用，在 ELEM 比较宏观其中：
I was wondering if theres an ELEM comparison macro in general use, where:
（V == ||一== v B）
可以替换为：
ELEM（V，A，B）
当然，这可以用宏做的，
Of course this can be done with a macro,
的#define ELEM（V，A，B）（（（五）==（a）条）||（（V）==（B）））
不过那你最终需要定义与说法计数多个宏。
However Then you end up needing to define multiple macros with argument counts.
使用我想出了这个简单的Python脚本：
Using a simple python script I came up with this:
#define ELEM2(v, a, b) \
(((v) == (a)) || ((v) == (b)))
#define ELEM3(v, a, b, c) \
(ELEM2(v, a, b) || ((v) == (c)))
#define ELEM4(v, a, b, c, d) \
(ELEM3(v, a, b, c) || ((v) == (d)))
#define ELEM5(v, a, b, c, d, e) \
(ELEM4(v, a, b, c, d) || ((v) == (e)))
#define ELEM6(v, a, b, c, d, e, f) \
(ELEM5(v, a, b, c, d, e) || ((v) == (f)))
#define ELEM7(v, a, b, c, d, e, f, g) \
(ELEM6(v, a, b, c, d, e, f) || ((v) == (g)))
#define ELEM8(v, a, b, c, d, e, f, g, h) \
(ELEM7(v, a, b, c, d, e, f, g) || ((v) == (h)))
#define ELEM9(v, a, b, c, d, e, f, g, h, i) \
(ELEM8(v, a, b, c, d, e, f, g, h) || ((v) == (i)))
#define ELEM10(v, a, b, c, d, e, f, g, h, i, j) \
(ELEM9(v, a, b, c, d, e, f, g, h, i) || ((v) == (j)))
#define ELEM11(v, a, b, c, d, e, f, g, h, i, j, k) \
(ELEM10(v, a, b, c, d, e, f, g, h, i, j) || ((v) == (k)))
#define ELEM12(v, a, b, c, d, e, f, g, h, i, j, k, l) \
(ELEM11(v, a, b, c, d, e, f, g, h, i, j, k) || ((v) == (l)))
#define ELEM13(v, a, b, c, d, e, f, g, h, i, j, k, l, m) \
(ELEM12(v, a, b, c, d, e, f, g, h, i, j, k, l) || ((v) == (m)))
#define ELEM14(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n) \
(ELEM13(v, a, b, c, d, e, f, g, h, i, j, k, l, m) || ((v) == (n)))
#define ELEM15(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) \
(ELEM14(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n) || ((v) == (o)))
#define ELEM16(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) \
(ELEM15(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) || ((v) == (p)))
从这个python3脚本：
From this python3-script:
ELEM_TOTAL = 16
for i in range(2, ELEM_TOTAL + 1):
print("#define ELEM%d(" % i, end="")
print("v, ", end="")
args = [chr(ord('a') + j) for j in range(i)]
print(", ".join(args), end="")
print(") \\\n (", end="")
if i == 2:
print("((v) == (a)) || ((v) == (b))", end="")
else:
print("ELEM%d(v, %s) || ((v) == (%s))" % (i - 1, ", ".join(args[:-1]), args[-1]), end="")
print(")")
但如果有常用的任何 ELEM 宏其接受可变数量的参数，而且我想知道至少有足够的便携式与流行的C编译器的工作（海合会，锵，英特尔，MCVC）。
But I was wondering if there are any ELEM macros in common use which accept a variable number of arguments and are at least portable enough to work with popular C compilers (GCC, Clang, Intel, MCVC).
推荐答案
根据答案来，我有一个可变参数ELEM宏我觉得挺作品可移植的，尽管它取决于 __ __ VA_ARGS ，但不认为这能有所帮助。
Based on the answer to this question, I have a varargs ELEM macro I think works quite portably, though it depends on __VA_ARGS__ but dont think that can be helped.
使用示例：
if (ELEM(var, A, B)) {
....
}
else if (ELEM(var, C, D, E, F, G)) {
....
}
执行力度：
#include <stdio.h>
/* ------ */
/* Macros */
/* internal helpers */
#define _VA_NARGS_GLUE(x, y) x y
#define _VA_NARGS_RETURN_COUNT(_1_, _2_, _3_, _4_, _5_, _6_, _7_, _8_, _9_, _10_, _11_, _12_, _13_, _14_, _15_, _16_, count, ...) count
#define _VA_NARGS_EXPAND(args) _VA_NARGS_RETURN_COUNT args
#define _VA_NARGS_COUNT_MAX16(...) _VA_NARGS_EXPAND((__VA_ARGS__, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0))
#define _VA_NARGS_OVERLOAD_MACRO2(name, count) name##count
#define _VA_NARGS_OVERLOAD_MACRO1(name, count) _VA_NARGS_OVERLOAD_MACRO2(name, count)
#define _VA_NARGS_OVERLOAD_MACRO(name, count) _VA_NARGS_OVERLOAD_MACRO1(name, count)
/* expose for re-use */
#define VA_NARGS_CALL_OVERLOAD(name, ...) _VA_NARGS_GLUE(_VA_NARGS_OVERLOAD_MACRO(name, _VA_NARGS_COUNT_MAX16(__VA_ARGS__)), (__VA_ARGS__))
/* ---------- */
/* ELEM Macro */
/* internal helpers*/
#define _VA_ELEM3(v, a, b) \
(((v) == (a)) || ((v) == (b)))
#define _VA_ELEM4(v, a, b, c) \
(_VA_ELEM3(v, a, b) || ((v) == (c)))
#define _VA_ELEM5(v, a, b, c, d) \
(_VA_ELEM4(v, a, b, c) || ((v) == (d)))
#define _VA_ELEM6(v, a, b, c, d, e) \
(_VA_ELEM5(v, a, b, c, d) || ((v) == (e)))
#define _VA_ELEM7(v, a, b, c, d, e, f) \
(_VA_ELEM6(v, a, b, c, d, e) || ((v) == (f)))
#define _VA_ELEM8(v, a, b, c, d, e, f, g) \
(_VA_ELEM7(v, a, b, c, d, e, f) || ((v) == (g)))
#define _VA_ELEM9(v, a, b, c, d, e, f, g, h) \
(_VA_ELEM8(v, a, b, c, d, e, f, g) || ((v) == (h)))
#define _VA_ELEM10(v, a, b, c, d, e, f, g, h, i) \
(_VA_ELEM9(v, a, b, c, d, e, f, g, h) || ((v) == (i)))
#define _VA_ELEM11(v, a, b, c, d, e, f, g, h, i, j) \
(_VA_ELEM10(v, a, b, c, d, e, f, g, h, i) || ((v) == (j)))
#define _VA_ELEM12(v, a, b, c, d, e, f, g, h, i, j, k) \
(_VA_ELEM11(v, a, b, c, d, e, f, g, h, i, j) || ((v) == (k)))
#define _VA_ELEM13(v, a, b, c, d, e, f, g, h, i, j, k, l) \
(_VA_ELEM12(v, a, b, c, d, e, f, g, h, i, j, k) || ((v) == (l)))
#define _VA_ELEM14(v, a, b, c, d, e, f, g, h, i, j, k, l, m) \
(_VA_ELEM13(v, a, b, c, d, e, f, g, h, i, j, k, l) || ((v) == (m)))
#define _VA_ELEM15(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n) \
(_VA_ELEM14(v, a, b, c, d, e, f, g, h, i, j, k, l, m) || ((v) == (n)))
#define _VA_ELEM16(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) \
(_VA_ELEM15(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n) || ((v) == (o)))
#define _VA_ELEM17(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) \
(_VA_ELEM16(v, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) || ((v) == (p)))
/* reusable ELEM macro */
#define ELEM(...) VA_NARGS_CALL_OVERLOAD(_VA_ELEM, __VA_ARGS__)
/* ------- */
/* Example */
int main(void)
{
int i;
i = 1 + 1;
printf("Test 1+1, in (3, 2, 1)? -> %d\n", ELEM(i, 3, 2, 1));
i = 22;
printf("Test 22, in (2/4, 10*2, 42, 100, 44/3)? -> %d\n", ELEM(i, 2 / 4, 10 * 2, 42, 100, 44 / 3));
return 0;
}
请注意， _VA_ELEM＃这个python3脚本生成的：
Note, _VA_ELEM# generated with this python3-script:
ELEM_TOTAL = 16
for i in range(2, ELEM_TOTAL + 1):
print("#define _VA_ELEM%d(" % (i + 1), end="")
print("v, ", end="")
args = [chr(ord('a') + j) for j in range(i)]
print(", ".join(args), end="")
print(") \\\n (", end="")
if i == 2:
print("((v) == (a)) || ((v) == (b))", end="")
else:
print("_VA_ELEM%d(v, %s) || ((v) == (%s))" % (i, ", ".join(args[:-1]), args[-1]), end="")
print(")")
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