# persistence/persistent_xref.hpp

    #ifndef STLPLUS_PERSISTENT_XREF
    #define STLPLUS_PERSISTENT_XREF
    ////////////////////////////////////////////////////////////////////////////////

    //   Author:    Andy Rushton
    //   Copyright: (c) Southampton University 1999-2004
    //              (c) Andy Rushton           2004 onwards
    //   License:   BSD License, see ../docs/license.html

    //   Persistence for cross-references to persistent objects

    //   A cross-reference is a pointer to an object that has definitely been dumped
    //   already by one of dump_pointer, dump_interface or dump_callback, i.e. by
    //   one of the dump routines for pointers to objects.

    //   These are typically used in data structures as back-pointers or pointers
    //   between nodes.

    //   For example, you may have a tree with cross links. Dump the tree as the
    //   primary data structure first, then dump the cross links as cross-references
    //   afterwards. The whole tree must be dumped before any cross-references to
    //   ensure that all cross-references are known to the persistence system.

    //   These functions will throw an exception if the cross-reference points to
    //   something not dumped before.

    ////////////////////////////////////////////////////////////////////////////////
    #include "persistence_fixes.hpp"
    #include "persistent_contexts.hpp"

    ////////////////////////////////////////////////////////////////////////////////

    namespace stlplus
    {

      // exceptions: persistent_dump_failed
      template<typename T>
      void dump_xref(dump_context&, const T* const data);

      // exceptions: persistent_dump_failed
      template<typename T>
      void dump_object_xref(dump_context&, const T* const data);

      // exceptions: persistent_restore_failed
      template<typename T>
      void restore_xref(restore_context&, T*& data);

      // exceptions: persistent_restore_failed
      template<typename T>
      void restore_object_xref(restore_context&, T*& data);

    } // end namespace stlplus

      ////////////////////////////////////////////////////////////////////////////////
    #include "persistent_xref.tpp"
    #endif