c - Why does this code produce an incomplete IP address? -

i reading buffer socket (af_packet, sock_dgram, htons(eth_p_arp)) following code. using arp_frame struct access component parts of contained arp reply. inet_ntoa() returns correct first octet of ip other octets 0 producing 172.0.0.0.

question 1 why might happen? question 2 how can print r bytes of msg buffer hex in host byte order debug packet?

    unsigned char msg[65535];     struct ether_arp *arp_frame = (struct ether_arp *)msg;      while ((r = recv(sock, msg, sizeof(msg), 0))) {             // skip it's not arp reply             if (ntohs(arp_frame->arp_op) != arpop_reply)                     continue;              (i = 0; < sonos_prefix_num; i++) {                     if (!memcmp(sonos_prefixes[i], arp_frame->arp_sha, 3)) {                             struct in_addr addr;                             addr.s_addr = *arp_frame->arp_spa;                              printf("blah: %lu\n", ntohl(*arp_frame->arp_spa));                             printf("sonos found @ %s\n", inet_ntoa(addr));                     }             }     } 

struct ether_arp looks this:

struct  ether_arp {     struct  arphdr ea_hdr;          /* fixed-size header */     u_int8_t arp_sha[eth_alen];     /* sender hardware address */     u_int8_t arp_spa[4];            /* sender protocol address */     u_int8_t arp_tha[eth_alen];     /* target hardware address */     u_int8_t arp_tpa[4];            /* target protocol address */ }; 

with in mind, think addr.s_addr = *arp_frame->arp_spa; looks little fishy. arp_frame->arp_spa yields u_int8_t[4], dereference pointer. think memcpy() might more appropriate there.