X-macros for enums

main.c

#include <stdio.h>
#include <string.h>

// Fully connected graph of transformations:
//   Message      (enum)
//   MessageIndex (enum)
//
//   Index -> Key
//   Index -> Value
//   Value -> Index (reverse lookup)
#define MESSAGES(X) \
    X(FOO, 0)       \
    X(BAR, 1)       \
    X(BAZ, 2)       \
    X(BOK, 7)

#define ENUM_KV(key, val) key = val,
#define ENUM_IDX(key, val) IDX_##key,
#define ENUM_KEYS(key, val) #key,
#define ENUM_VALS(key, val) val,
#define ENUM_CASES(key, val) case(key): { return IDX_##key; }

#define GEN_ENUM(name, max, xs)                       \
    typedef enum { xs(ENUM_KV) } name;                \
    enum { xs(ENUM_IDX) max };                        \
    static const char *keys[max] = { xs(ENUM_KEYS) }; \
    static const int vals[max] = { xs(ENUM_VALS) };   \
    int index_of(name x) {                            \
        switch(x) {                                   \
            xs(ENUM_CASES)                            \
        default: { return -1; }                       \
        }                                             \
    }

GEN_ENUM(Message, NUM_MESSAGES, MESSAGES)

int main(void) {
    for (size_t i = 0; i < NUM_MESSAGES; i += 1) {
        Message msg = vals[i];
        printf("[%zu] \"%s\": %d\n", i, keys[i], vals[i]);
    }
    return 0;
}