Question

I am trying to implement a simple client that connects to a give address. You’ll notice that I’m printing the given address and the IP address and port after I put it in my sockaddr_in struct.
I get two different addresses even though it should be the same.

Here’s my code:

int createConnection(char * address, char * port) {
    cout << address << " " << port << endl;
    struct sockaddr_in server;
    server.sin_family = AF_INET;
    server.sin_port = htons(atoi(port));
    inet_aton(address,&(server.sin_addr));
    memset(&(server.sin_zero), '\0', 8);
    if ((sockFd = socket(PF_INET,SOCK_STREAM,0)) == -1) {
        perror("client: socket");
    }
    if (connect(sockFd,(const sockaddr *)&server,sizeof(struct sockaddr_in)) == -1) {
        close(sockFd);
        perror("client: connect");
    }

    char s[INET_ADDRSTRLEN];
    inet_ntop(AF_INET, (struct sockaddr *)&server, s, sizeof s);
    printf("client: connecting to %s, %i\n", s, server.sin_port);
    printf("connected");
    return 0;
}

And the output is

132.65.151.39 3000
client: connecting to 2.0.11.184, 47115

My questions:

1. Why do I see two different addresses?
2. How come the connection does not fail?

What happens is that my program is blocked in recv() later on, so I think it didn’t connect to where I wanted it. Thanks!

Answer 1

It looks like you’re passing the wrong thing to inet_ntop():

inet_ntop(AF_INET, (struct sockaddr *)&server, s, sizeof s);

You should probably be passing .sin_addr:

inet_ntop(AF_INET, &server.sin_addr, s, sizeof s);

For the port, it prints wrong because you need to call ntohs() to convert back to host byte order:

printf("client: connecting to %s, %i\n", s, ntohs(server.sin_port));

The connection works, presumably because the address is set correctly, in actuality.