C / binding multiple sockets [on differnet ports] - c

Question

I want to bind 4 sockets on different ports. Somehow I get always the : Address already in use error. For the first loop, the case PORT1 it is working, but when coming to the second run I get the above mentioned error. It would be nice, if someone could take a closer look at my code.
The output looks like that:
thread 0 started, pc_packet_receiver
sock_fd[8]
sock_fd[8], fdmax[8]
sock_fd[9]
error: could not bind UDP socket, port2
: Address already in use
As you can see, the first printf in the loop is processed twice and when bind is called for PORT2 the program crashes.
sock_fd is an array of file descriptors
sock_addr_port[1..4] are four different struct sock_addr
the values PORT1/PORT2/PORT3/PORT4 are defined in an enum [1..4]
in the end I want to add all sock_fd[i] into a FD_SET to processing them with select
thank you very much in advance for your help.
for(i = 0; i < 4; i++) {
if((sock_fd[i] = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
perror("error: could not open UDP socket\n");
exit(EXIT_FAILURE);
}
printf("\tsock_fd[%d]\n", sock_fd[i]);
switch (i+1) {
case PORT1:
bzero(&sock_addr_port1, sock_len_port1);
sock_addr_port1.sin_family = AF_INET;
sock_addr_port1.sin_port = htons(ETH_PORT1);
sock_addr_port1.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sock_fd[i], (struct sockaddr *) &sock_addr_port1, sock_len_port1) < 0) {
perror("error: could not bind UDP socket, port1\n");
exit(EXIT_FAILURE);
}
break;
case PORT2:
bzero(&sock_addr_port2, sock_len_port2);
sock_addr_port2.sin_family = AF_INET;
sock_addr_port2.sin_port = htons(ETH_PORT2);
sock_addr_port2.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sock_fd[i], (struct sockaddr *) &sock_addr_port2, sock_len_port2) < 0) {
perror("error: could not bind UDP socket, port2\n");
exit(EXIT_FAILURE);
}
break;
case PORT3:
bzero(&sock_addr_port3, sock_len_port3);
sock_addr_port3.sin_family = AF_INET;
sock_addr_port3.sin_port = htons(ETH_PORT3);
sock_addr_port3.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sock_fd[i], (struct sockaddr *) &sock_addr_port3, sock_len_port3) < 0) {
perror("error: could not bind UDP socket, port3\n");
exit(EXIT_FAILURE);
}
break;
case PORT4:
bzero(&sock_addr_port4, sock_len_port4);
sock_addr_port4.sin_family = AF_INET;
sock_addr_port4.sin_port = htons(ETH_PORT4);
sock_addr_port4.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sock_fd[i], (struct sockaddr *) &sock_addr_port4, sock_len_port4) < 0) {
perror("error: could not bind UDP socket, port4\n");
exit(EXIT_FAILURE);
}
break;
default:
break;
}
FD_SET(sock_fd[i], &read_fds);
fdmax = sock_fd[i];
printf("sock_fd[%d], fdmax[%d]\n", sock_fd[i], fdmax);
}

Answer 1

There is another process running which uses ETH_PORT2 right now. You should be able to see this when you run netstat -tan (-tn on Windows) on the command line.
Google for "which process uses which port" to see how you can find out the process.