printf “__be32” value type

Question

I use this "struct iphdr* ip_reply" to read received packet with this function :

recvfrom(sockfd, buffer, sizeof(struct iphdr) + sizeof(struct icmphdr), 0, (struct sockaddr *)&connection, &addrlen))

ip_reply = (struct iphdr*) buffer; // casting => read ip header from received packet

this is the struct parameter :

      struct iphdr {  #if defined(__LITTLE_ENDIAN_BITFIELD)
     __u8    ihl:4,
            version:4;  #elif defined (__BIG_ENDIAN_BITFIELD)
     __u8    version:4,
             ihl:4;

   __u8    tos;
   __be16  tot_len;
   __be16  id;
   __be16  frag_off;
   __u8    ttl;
   __u8    protocol;
   __sum16 check;
   __be32  saddr;
   __be32  daddr;
    /*The options start here. */  };

how can I display "saddr" "daddr" with printf?

Amadeus Amadeus · Accepted Answer · 2013-07-04T15:51:05

There is a group of function in libc that deals with those transformations. In your case, you can use the function: inet_ntoa(). Basically, it get an address in network binary format (network byte order) and retrieve an IPv4 address, using dot notation, into a string.

If you are using a unix SO, I suggest you to look at man pages to see the correct usage.

printf “__be32” value type

2 Answers