The LDAP API defines various data structures which are used to
    pass information to and from a client application. Some of these
    structures are opaque; that is, their internal layout is not
    visible to a client application. In such cases, the API may
    return a pointer to such a structure, but the only use of such
    a pointer to a client application is as a parameter to subsequent
    library calls.

    Some structures are public. Their contents are defined by the
    API, and client applications may allocate and manipulate such
    structures or use them as parameters to LDAP functions.

    All data structures used by the API are defined with "natural"
    alignment; that is, each member of a data structure will be
    aligned on an address boundary appropriate to its type.

    Opaque Data Structures

    The following data structures are opaque. Applications should
    not make any assumptions about the contents or size of such data
    structures.

        typedef struct ldap
                LDAP;

        typedef struct ldapmsg
                LDAPMessage;

        typedef struct berelement
                BerElement;

    Public Data Structures

    The following data structures are described in the IETF documents
    relating to the LDAP API, and definitions are provided for
    them in LDAP.H. Applications may allocate and manipulate such
    structures, as well as use them in calls to the LDAP API.

        typedef struct berval { .. }
                BerValue;

        typedef struct ldapapiinfo { .. }
                LDAPAPIInfo;

        typedef struct ldap_apifeature_info { .. }
                LDAPAPIFeatureInfo;

        typedef struct ldapcontrol { .. }
                LDAPControl;

        typedef struct ldapmod { .. }
                LDAPMod;

    Note that the pointer size in effect at compilation time
    determines the layout of data structures, which themselves
    contain pointer fields. Since all of the public data structures
    listed here contain one or more pointers, their size and layout
    will differ depending on the pointer size.

    For example, in the case of the structure berval, the API
    provides the following definition:

     struct berval {
          ber_len_t      bv_len;
          char           *bv_val;
     } BerValue;

    (where ber_len_t is equivalent on OpenVMS to an unsigned 32-bit
    integer).

    The following code would therefore work correctly regardless of
    pointer size:

         #include <ldap.h>
         .
         .
         .
           char       *buff;
           BerValue   val;
         .
         .
         .
           buff = (char *)malloc(255);
         .
         .
         .
           val.bv_len = 255;
           val.bv_val = buff;
         .
         .
         .