Enumerates all index selections for a dynamic number of arrays with different sizes

enumerate_selection.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h> // not required in C23 anymore

/**
 * Enumerate all index combinations.
 * 
 * The @p indices array shall be initially @c NULL and
 * will be allocated by this function and must be passed
 * free().
 *
 * @param indices the target index array that will be enumerated
 * @param sizes the array containing the non-zero sizes
 * @param len the length of @p sizes / the number of arrays
 * @return @c true if a new combination was generated,
 *         @c false if all combinations have been enumerated
 */
bool enumerate_selections(size_t** indices, const size_t* sizes, size_t len) {
    if (*indices == NULL) { // you may want to use nullptr in C23
        *indices = calloc(len, sizeof(size_t));
        return true;
    }
    for (size_t i = 0; i < len; i++) {
        (*indices)[i]++;
        if ((*indices)[i] >= sizes[i]) {
            (*indices)[i] = 0;
            if (i == len - 1) {
                return false;
            }
        } else {
            break;
        }
    }
    return true;
}

// A simple test program.
int main(void) { 

    // expected output is an enumeration of all
    // combination of indices for five hypothetical
    // arrays with the sizes stored in the test array
    size_t test[5] = {3, 7, 2, 4, 5};
    size_t *indices = NULL;
    while (enumerate_selections(&indices, test, 5)) {
        for (size_t i = 0 ; i < 5 ; i++) {
            printf("%zu ", indices[i]);
        }
        putchar('\n');
    }
    free(indices);

    return 0;
}