The ldap_first_attribute() and ldap_next_attribute()  calls are
    used to step through the list of attribute types returned with an
    entry.

            char *ldap_first_attribute(
                    LDAP                                    *ld,
                    LDAPMessage                             *entry,
                    BerElement                              **ptr
            );

            char *ldap_next_attribute(
                    LDAP                                    *ld,
                    LDAPMessage                             *entry,
                    BerElement                              *ptr
            );

            void ldap_memfree( char *mem );

    Parameters are as follows:

    ld    The session handle.
    entry The entry whose attributes are to be stepped through, as
          returned by ldap_first_entry()  or ldap_next_entry().
    ptr   In ldap_first_attribute(),  the address of a pointer used
          internally to keep track of the current position in the
          entry. In ldap_next_attribute(),  the pointer returned by a
          previous call to ldap_first_attribute().
    mem   A pointer to memory allocated by the LDAP library, such
          as the attribute type names returned by ldap_first_
          attribute()  and ldap_next_attribute(), or the DN returned
          by ldap_get_dn().

    The ldap_first_attribute() and ldap_next_attribute()  functions
    will return NULL when the end of the attributes is reached, or
    if there is an error, in which case the error parameters in the
    session handle ld will be set to indicate the error.

    Both functions return a pointer to an allocated buffer containing
    the current attribute name. This should be freed when no longer
    in use by calling ldap_memfree().

    The ldap_first_attribute() function will allocate and return in
    ptr a pointer to a BerElement used to keep track of the current
    position. This pointer should be passed in subsequent calls to
    ldap_next_attribute() to step through the entry's attributes.
    After a set of calls to ldap_first_attribute() and ldap_next_
    attribute(), if ptr is non-NULL, it should be freed by calling
    ber_free(ptr, 0). Note that it is very important to pass the
    second parameter as 0 (zero) in this call, since the buffer
    associated with the BerElement does not point to separately
    allocated memory.

    The attribute type names returned are suitable for passing in a
    call to ldap_get_values() to retrieve the associated values.