array_cat.c

/* I hearby do solemnly declare this to be the most beautiful abuse of preprocessor macros and structs I've ever committed. */

#define ARRAY_CAT(type, array, ...) (*(type (*)[sizeof (array) / sizeof (type) + sizeof ((type[]) { __VA_ARGS__ }) / sizeof (type)]) &(struct { type foo[sizeof (array) / sizeof (*array)]; type bar[sizeof ((type[]) { __VA_ARGS__ }) / sizeof (type)]; }) { .foo = array, .bar = { __VA_ARGS__ } })

#include <stdio.h>

int main(void) {
    const int array_1[] = { 0, 1, 2, 3 };
    const int array_2[] = ARRAY_CAT(int, array_1, 4, 5, 6, 7, 8);
    const int array_3[] = ARRAY_CAT(int, array_1, 10, 11, 12);

    printf("%zu %zu %zu\n", sizeof array_1, sizeof array_2, sizeof array_3);
}