Programming Interfaces Guide

Sockets and Clients

This section describes the steps taken by a client process. As in the server, the first step is to locate the service definition for a remote login.

bzero(&hints, sizeof (hints));
hints.ai_flags = AI_ALL|AI_ADDRCONFIG;
hints.ai_socktype = SOCK_STREAM;

error = getaddrinfo(hostname, servicename, &hints, &res);
if (error != 0) {
    (void) fprintf(stderr, "getaddrinfo: %s for host %s service %s\n",
        gai_strerror(error), hostname, servicename);
    return (-1);

getaddrinfo(3SOCKET) returns the head of a list of addresses in res. The desired address is found by creating a socket and trying to connect to each address returned in the list until one works.

for (aip = res; aip != NULL; aip = aip->ai_next) {
     * Open socket.  The address type depends on what
     * getaddrinfo() gave us.
    sock = socket(aip->ai_family, aip->ai_socktype,
    if (sock == -1) {
        return (-1);

    /* Connect to the host. */
    if (connect(sock, aip->ai_addr, aip->ai_addrlen) == -1) {
        (void) close(sock);
        sock = -1;

The socket has been created and has been connected to the desired service. The connect(3SOCKET) routine implicitly binds sock, because sock is unbound.