用于 C 的 Varargs `ELEM` 宏 [英] Varargs `ELEM` macro for use with C

问题描述

我想知道是否有一个通用的 ELEM 比较宏，其中:

I was wondering if theres an ELEM comparison macro in general use, where:

(v == a || v == b)

可以替换为:

ELEM(v, a, b)

当然这可以通过宏来完成，

Of course this can be done with a macro,

#define ELEM(v, a, b) (((v) == (a)) || ((v) == (b)))

但是，您最终需要使用参数计数定义多个宏.

However Then you end up needing to define multiple macros with argument counts.

使用一个简单的 python 脚本我想出了这个:

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)))

来自这个 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(") \
       (", 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(")")

但我想知道是否有任何常用的 ELEM 宏可以接受可变数量的参数，并且至少可移植到足以与流行的 C 编译器(GCC、Clang、Intel、MCVC)一起使用).

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

基于这个问题的答案，我有一个可变参数 ELEM 宏，我认为它可以很好地移植，虽然它依赖于 __VA_ARGS__ 但我认为这无济于事.

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)) {
    ....
}

实施:

#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
", ELEM(i, 3, 2, 1));

    i = 22;
    printf("Test 22, in (2/4, 10*2, 42, 100, 44/3)? -> %d
", ELEM(i, 2 / 4, 10 * 2, 42, 100, 44 / 3));
    return 0;
}

注意，_VA_ELEM# 使用此 python3 脚本生成:

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(") \
       (", 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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