The ldap_init() function initializes a session with an LDAP
    server. The server is not actually contacted until an operation
    is performed that requires it, allowing various options to be set
    after initialization.

            LDAP *ldap_init(
                  const char    *hostname,
                  int           portno);

    Use of the following function is deprecated.

            LDAP *ldap_open(
                  const char    *hostname,
                  int           portno);

    Unlike ldap_init(), the ldap_open()  function attempts to make a
    server connection before returning to the caller. A more complete
    description can be found in RFC 1823.

    Parameters are as follows:

    hostname   Contains a space-separated list of hostnames or dotted
               strings representing the IP address of hosts running an
               LDAP server to connect to. Each hostname in the list
               can include an optional port number which is separated
               from the host itself with a colon (:) character. The
               hosts are tried in the order listed, stopping with
               the first one to which a successful connection is
               made. Note that only ldap_open() attempts to make the
               connection before returning to the caller. ldap_init()
               does not connect to the LDAP server.
    portno     Contains the TCP port number to connect to. The default
               LDAP port of 389 can be obtained by supplying the
               constant LDAP_PORT. If a host includes a port number,
               then this parameter is ignored.

    The ldap_init() and ldap_open()  functions both return a session
    handle, a pointer to an opaque structure that should be passed
    to subsequent calls pertaining to the session. These functions
    return NULL if the session cannot be initialized, in which case
    the operating system error reporting mechanism can be checked to
    see why the call failed.

    Note that if you connect to an LDAP Version 2 server, one of the
    ldap_bind() calls must be completed before other operations can
    be performed on the session. LDAPv3 does not require that a bind
    operation be completed before other operations can be performed.

    The calling program can set various attributes of the session
    by calling the functions described in the Session Handles help
    topic.