1 /* Boost.MultiIndex example of serialization of a MRU list.
2 *
3 * Copyright 2003-2008 Joaquin M Lopez Munoz.
4 * Distributed under the Boost Software License, Version 1.0.
5 * (See accompanying file LICENSE_1_0.txt or copy at
6 * http://www.boost.org/LICENSE_1_0.txt)
7 *
8 * See http://www.boost.org/libs/multi_index for library home page.
9 */
10
11 #if !defined(NDEBUG)
12 #define BOOST_MULTI_INDEX_ENABLE_INVARIANT_CHECKING
13 #define BOOST_MULTI_INDEX_ENABLE_SAFE_MODE
14 #endif
15
16 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
17 #include <algorithm>
18 #include <boost/archive/text_oarchive.hpp>
19 #include <boost/archive/text_iarchive.hpp>
20 #include <boost/multi_index_container.hpp>
21 #include <boost/multi_index/hashed_index.hpp>
22 #include <boost/multi_index/identity.hpp>
23 #include <boost/multi_index/sequenced_index.hpp>
24 #include <fstream>
25 #include <iostream>
26 #include <iterator>
27 #include <sstream>
28 #include <string>
29
30 using namespace boost::multi_index;
31
32 /* An MRU (most recently used) list keeps record of the last n
33 * inserted items, listing first the newer ones. Care has to be
34 * taken when a duplicate item is inserted: instead of letting it
35 * appear twice, the MRU list relocates it to the first position.
36 */
37
38 template <typename Item>
39 class mru_list
40 {
41 typedef multi_index_container<
42 Item,
43 indexed_by<
44 sequenced<>,
45 hashed_unique<identity<Item> >
46 >
47 > item_list;
48
49 public:
50 typedef Item item_type;
51 typedef typename item_list::iterator iterator;
52
mru_list(std::size_t max_num_items_)53 mru_list(std::size_t max_num_items_):max_num_items(max_num_items_){}
54
insert(const item_type & item)55 void insert(const item_type& item)
56 {
57 std::pair<iterator,bool> p=il.push_front(item);
58
59 if(!p.second){ /* duplicate item */
60 il.relocate(il.begin(),p.first); /* put in front */
61 }
62 else if(il.size()>max_num_items){ /* keep the length <= max_num_items */
63 il.pop_back();
64 }
65 }
66
begin()67 iterator begin(){return il.begin();}
end()68 iterator end(){return il.end();}
69
70 /* Utilities to save and load the MRU list, internally
71 * based on Boost.Serialization.
72 */
73
save_to_file(const char * file_name) const74 void save_to_file(const char* file_name)const
75 {
76 std::ofstream ofs(file_name);
77 boost::archive::text_oarchive oa(ofs);
78 oa<<boost::serialization::make_nvp("mru",*this);
79 }
80
load_from_file(const char * file_name)81 void load_from_file(const char* file_name)
82 {
83 std::ifstream ifs(file_name);
84 if(ifs){
85 boost::archive::text_iarchive ia(ifs);
86 ia>>boost::serialization::make_nvp("mru",*this);
87 }
88 }
89
90 private:
91 item_list il;
92 std::size_t max_num_items;
93
94 /* serialization support */
95
96 friend class boost::serialization::access;
97
98 template<class Archive>
serialize(Archive & ar,const unsigned int)99 void serialize(Archive& ar,const unsigned int)
100 {
101 ar&BOOST_SERIALIZATION_NVP(il);
102 ar&BOOST_SERIALIZATION_NVP(max_num_items);
103 }
104 };
105
main()106 int main()
107 {
108 const char* mru_store="mru_store";
109
110 /* Construct a MRU limited to 10 items and retrieve its
111 * previous contents.
112 */
113
114 mru_list<std::string> mru(10);
115 mru.load_from_file(mru_store);
116
117 /* main loop */
118
119 for(;;){
120 std::cout<<"enter a term: ";
121
122 std::string line;
123 std::getline(std::cin,line);
124 if(line.empty())break;
125
126 std::string term;
127 std::istringstream iss(line);
128 iss>>term;
129 if(term.empty())break;
130
131 mru.insert(term);
132
133 std::cout<<"most recently entered terms:"<<std::endl;
134 std::copy(
135 mru.begin(),mru.end(),
136 std::ostream_iterator<std::string>(std::cout,"\n"));
137 }
138
139 /* persist the MRU list */
140
141 mru.save_to_file(mru_store);
142
143 return 0;
144 }
145