C Challenge

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

enum _error_codes {
    NO_ARGS_ERR = -1,
    JOINING_ERR = -2
};

/* Function Declerations */

char *join_args(size_t, char *[], const char);
void swap(char *, char *);
void reverse(char *, size_t);
char *reverse_words(char *, const char);

int main(int argc, char *argv[]) {
    argc--; argv++;
    if (!argc)
        return NO_ARGS_ERR;

    char *joined = join_args(argc, argv, ' ');
    if (joined == NULL)
        return JOINING_ERR;

    printf("Reversed: %s\n", reverse_words(joined, ' '));

    free(joined);
    return 0;
}

/* Function Definitions */

char *join_args(size_t size, char *args[], const char delimiter) {
    if (!size) return NULL;

    size_t allocation_size = 0;
    size_t arg_lengths[size];

    // Accumulate allocation size and determine the lengths of each argument
    for (int i = 0; i < size; i++) {
        arg_lengths[i] = strlen(args[i]);
        allocation_size += arg_lengths[i] + 1;
    }

    // Allocate memory and combine arguments
    char *ret = malloc(allocation_size), *ptr = ret;
    for (int i = 0; i < size; i++) {
        strcpy(ptr, args[i]);
        ptr[ arg_lengths[i] ] = ' ';
        ptr += arg_lengths[i] + 1;
    }
    *--ptr = '\0';
    return ret;
}

void swap(char *a, char *b) {
    char temp = *a;
    *a = *b;
    *b = temp;
}

void reverse(char *str, size_t size) {
    if (!size) return;

    unsigned left = 0, right = size - 1;
    while (left < right)
        swap(&str[left++], &str[right--]);
}

char *reverse_words(char *str, const char delimiter) {
    char *ret = str;
    size_t index = 0;

    // Reverse the entire string then reverse the characters of
    // every word seperated by the delimiter or up to the NULL-terminator
    reverse(str, strlen(str));
    while (str[index] != '\0') {
        if (str[index] == delimiter) {
            reverse(str, index);
            str += index + 1;
            index = 0;
            continue;
        }
        index++;
    }
    reverse(str, index);

    return ret;
}