Program Statement

Connect a TCP socket to a remote host, then introspect both ends of the connection — getsockname for the local address, getpeername for the remote address. (The experiment list includes this twice — demonstrate both directions.)

/* sockaddrs.c — connect somewhere, then introspect both ends */
int main(void) {
    int fd = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in srv = {0};
    srv.sin_family = AF_INET; srv.sin_port = htons(80);
    inet_pton(AF_INET, "93.184.216.34", &srv.sin_addr);   /* example.com */
    connect(fd, (struct sockaddr *)&srv, sizeof(srv));

    struct sockaddr_in local, remote; socklen_t len; char ip[INET_ADDRSTRLEN];

    len = sizeof(local);
    getsockname(fd, (struct sockaddr *)&local, &len);     /* LOCAL end  */
    inet_ntop(AF_INET, &local.sin_addr, ip, sizeof(ip));
    printf("local:  %s:%d\n", ip, ntohs(local.sin_port)); /* ephemeral port! */

    len = sizeof(remote);
    getpeername(fd, (struct sockaddr *)&remote, &len);    /* REMOTE end */
    inet_ntop(AF_INET, &remote.sin_addr, ip, sizeof(ip));
    printf("remote: %s:%d\n", ip, ntohs(remote.sin_port));
    close(fd); return 0;
}

Record Task

Run the program twice — watch the local ephemeral port change between runs while the remote end stays fixed.

Theory Link

Unit 1 "Socket Address Structures" — this is the value-result argument in action: len is passed in with the buffer size and comes back with the actual address length.