Bind failed: : Address family not supported by protocol family - C - c

Question

I've declared a struct sockaddr_in server in my main function.
I pass it into this function to return a socket file descriptor
int openSocket(char* ip_addr, int port, struct sockaddr_in* server){
int sockfd, len;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if(sockfd < 0){
perror("Failed to open socket: ");
exit(-1);
}
len = sizeof(server);
bzero(server, len);
server->sin_family= AF_INET;
inet_pton(AF_INET, ip_addr, &server->sin_addr);
server->sin_port= htons(port);
if((bind(sockfd, (struct sockaddr*)&server, len)) < 0){
perror("Bind failed: ");
exit(-1);
}
return sockfd;
}
The struct is passed into the function using this call
sockfd = openSocket(vector->ip_addr, vector->port, &server);
However I get the following error.
Bind failed: : Address family not supported by protocol family

Answer 1

len = sizeof(server);
This determines the size of the pointer. You want the size of the structure it points to, so this should be:
len = sizeof(*server);

Answer 2

int openSocket(char* ip_addr, int port, struct sockaddr_in* server){
[...]
if((bind(sockfd, (struct sockaddr*)&server, len)) < 0){
server is already declared as a pointer, so I think the & operator
isn't needed in the bind() call.

Answer 3

int openSocket(char* ip_addr, int port, struct sockaddr_in* server){
This is interesting - you use sockaddr_in which has the following properties you need to set:
sun_family -- This must equal AF_INET.
sin_addr -- This is another structure with an unsigned long named s_addr which you'll probably want to set to INADDR_ANY +.
sin_port -- This requires a server port which needs converting with htons(). (Make sure this port is not in use ++! My go-to port is 3333 for testing...)
It seems you're using inet_pton() but I'm not sure it has the same affect for setting sin_port. Other that it looks fine.
The other area is there might be an issue is this line:
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
The 0 on the end specifies [1]:
"Specifying a protocol of 0 causes socket() to use an unspecified default protocol appropriate for the requested socket type."
I could imagine a possibility where the unspecified default is either not correct for your Operating System or that there is no default. I would try SOCK_STREAM to test whether this works.
+ NOTE: This would technically need htonl() but my understanding an this does nothing for this particular case.
++ NOTE: If you are writing client and server applications remember to be careful about which owns the port.
[1] http://pubs.opengroup.org/onlinepubs/009695399/functions/socket.html