troubleshooting Question

printf the IP address used to send a datagram

Avatar of jchristn123
jchristn123 asked on
CC++
22 Comments2 Solutions528 ViewsLast Modified:
How do I fetch the source IP address used out of a simple transmission?  For instance, if my UDP client code is:

int main(int argc, char *argv[])
{
   int sock, length, fromlen, n;
   struct sockaddr_in server;
   struct sockaddr_in from;
   char buf[1024];

   if (argc < 2) {
      fprintf(stderr, "ERROR, no port provided\n");
      exit(0);
   }
   
   sock=socket(AF_INET, SOCK_DGRAM, 0);
   if (sock < 0) error("Opening socket");
   length = sizeof(server);
   bzero(&server,length);
   server.sin_family=AF_INET;
   server.sin_addr.s_addr=INADDR_ANY;
   server.sin_port=htons(atoi(argv[1]));
   if (bind(sock,(struct sockaddr *)&server,length)<0)
       error("binding");
   fromlen = sizeof(struct sockaddr_in);
   while (1) {
       n = recvfrom(sock,buf,1024,0,(struct sockaddr *)&from,&fromlen);
       if (n < 0) error("recvfrom");
       write(1,"Received a datagram: ",21);
       write(1,buf,n);
       n = sendto(sock,"Got your message\n",17,
                  0,(struct sockaddr *)&from,fromlen);
       if (n  < 0) error("sendto");
   }
 }

How do I printf the IP address I used in sending the datagram as a string (not the destination address)?

Thanks!
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