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libs/multi_index/example/serialization.cpp

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+/* Boost.MultiIndex example of serialization of a MRU list.
+ *
+ * Copyright 2003-2008 Joaquin M Lopez Munoz.
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ *
+ * See http://www.boost.org/libs/multi_index for library home page.
+ */
+
+#if !defined(NDEBUG)
+#define BOOST_MULTI_INDEX_ENABLE_INVARIANT_CHECKING
+#define BOOST_MULTI_INDEX_ENABLE_SAFE_MODE
+#endif
+
+#include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
+#include <algorithm>
+#include <boost/archive/text_oarchive.hpp>
+#include <boost/archive/text_iarchive.hpp>
+#include <boost/multi_index_container.hpp>
+#include <boost/multi_index/hashed_index.hpp>
+#include <boost/multi_index/identity.hpp>
+#include <boost/multi_index/sequenced_index.hpp>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <sstream>
+#include <string>
+
+using namespace boost::multi_index;
+
+/* An MRU (most recently used) list keeps record of the last n
+ * inserted items, listing first the newer ones. Care has to be
+ * taken when a duplicate item is inserted: instead of letting it
+ * appear twice, the MRU list relocates it to the first position.
+ */
+
+template <typename Item>
+class mru_list
+{
+  typedef multi_index_container<
+    Item,
+    indexed_by<
+      sequenced<>,
+      hashed_unique<identity<Item> >
+    >
+  > item_list;
+
+public:
+  typedef Item                         item_type;
+  typedef typename item_list::iterator iterator;
+
+  mru_list(std::size_t max_num_items_):max_num_items(max_num_items_){}
+
+  void insert(const item_type& item)
+  {
+    std::pair<iterator,bool> p=il.push_front(item);
+
+    if(!p.second){                     /* duplicate item */
+      il.relocate(il.begin(),p.first); /* put in front */
+    }
+    else if(il.size()>max_num_items){  /* keep the length <= max_num_items */
+      il.pop_back();
+    }
+  }
+
+  iterator begin(){return il.begin();}
+  iterator end(){return il.end();}
+
+  /* Utilities to save and load the MRU list, internally
+   * based on Boost.Serialization.
+   */
+
+  void save_to_file(const char* file_name)const
+  {
+    std::ofstream ofs(file_name);
+    boost::archive::text_oarchive oa(ofs);
+    oa<<boost::serialization::make_nvp("mru",*this);
+  }
+
+  void load_from_file(const char* file_name)
+  {
+    std::ifstream ifs(file_name);
+    if(ifs){
+      boost::archive::text_iarchive ia(ifs);
+      ia>>boost::serialization::make_nvp("mru",*this);
+    }
+  }
+
+private:
+  item_list   il;
+  std::size_t max_num_items;
+
+  /* serialization support */
+
+  friend class boost::serialization::access;
+    
+  template<class Archive>
+  void serialize(Archive& ar,const unsigned int)
+  {
+    ar&BOOST_SERIALIZATION_NVP(il);
+    ar&BOOST_SERIALIZATION_NVP(max_num_items);
+  }
+};
+
+int main()
+{
+  const char* mru_store="mru_store";
+
+  /* Construct a MRU limited to 10 items and retrieve its
+   * previous contents.
+   */
+
+  mru_list<std::string> mru(10);
+  mru.load_from_file(mru_store);
+
+  /* main loop */
+
+  for(;;){
+    std::cout<<"enter a term: ";
+
+    std::string line;
+    std::getline(std::cin,line);
+    if(line.empty())break;
+
+    std::string term;
+    std::istringstream iss(line);
+    iss>>term;
+    if(term.empty())break;
+
+    mru.insert(term);
+
+    std::cout<<"most recently entered terms:"<<std::endl;
+    std::copy(
+      mru.begin(),mru.end(),
+      std::ostream_iterator<std::string>(std::cout,"\n"));
+  }
+
+  /* persist the MRU list */
+
+  mru.save_to_file(mru_store);
+
+  return 0;
+}