2011/11/23 Claude <clros@tiscali.it>:

I used this definition:

typedef multi_index_container<  int,  indexed_by<sequenced<> >

...

mySet;

But this not preserve the insertion order. I think that my error is in "index_by<>"; it is true? How do I fix?

First of all: do you need key-value container (map/hash map) or just sequential one (list/vector)? If you need it to be both at the same time, multi-index is the way to go then and you need need 2 indices, ordered and sequenced, for example: typedef multi_index_container< std::string, indexed_by< sequenced<>, ordered_unique<identity<std::string> >

text_container;

Cheers, Simon -- Szymon Gatner The Lordz Games Studio www.thelordzgamesstudio.com

On 23 November 2011 15:17, Claude <clros@tiscali.it> wrote:

I need a set and also a map.

std::unordered_map Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

On 23 November 2011 15:47, Claude <clros@tiscali.it> wrote:

C++11 std::unordered_map store elements with no insertion order but based on a hash function...

Yes, but you can easily combine it with sequential container that tracks order, but maps gives mapping, without sorting 'overhead'. Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

On Wed, Nov 23, 2011 at 10:17 AM, Claude <clros@tiscali.it> wrote:

I need a set and also a map. But not at the same time.

boost multiindex will allow this. I have done this several times in my applications. John

On Wed, Nov 23, 2011 at 10:11 AM, Claude <clros@tiscali.it> wrote:

It is very difficult to realize?

No. The examples are pretty straightforward. Even I understood them, and that's saying quite a lot. I used the tutorial as well as the examples to get myself going. http://www.boost.org/doc/libs/1_47_0/libs/multi_index/doc/examples.html -- Chris Cleeland

       indexed_by<                random_access<>,                ordered_non_unique<member<item, int, &item::i_> >        >

(of course, you can omit the second ordered_non_unique<> index, if you don't need it)

but if I would simulate a std::map I should add another field in structure, to store the "value" of the map .. is correct?

Yes, you can add a "key" field to the struct, and then define ordered unique index on it. Note that when accessing multi_index_container you say explicitly which index you're working with. So, when you're working with random_access<> index, you'll get the items in the order of insertion, but when you switch to another (eg. ordered) index, you get the items in another order.

Ok, it is good! Last question:it is possible to insert an element with equal syntax of std::map (eg. myMap[myKey] = myValue;)?

No, it's impossible. Please read the following: http://www.boost.org/doc/libs/1_48_0/libs/multi_index/doc/tutorial/technique...

I was trying to encapsulate a boost multiindex in a class usable as std:: map. This is code: template<typename K,typename V> class Ordered_Map { private: struct item { item(K k,V v) : first(k),second(v) {} K first; V second; }; typedef multi_index_container< item, indexed_by< random_access<>, ordered_unique<member<item, K, &item::first> > > > container; container c; public: V operator[](const K& key) { c.insert(c.end(), item(key,2)); return (??); } void begin() { //for (container::const_iterator i = c.begin(); i != c.end(); ++i) //std::cout << i->first << " - " << i->second << std::endl; } }; I have some problems; The operator[] is not yet complete. But the real problem is the begin() method, it should return a container::const_iterator, but if I use the signature: *container::const_iterator begin()* { return c.begin(); } I get an error :-( If I use container::const_iteraton inside the method begin() as type..it work as type, but it don't work as returned type of begin()! -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

How can I return second index iterator? Why if I use container::const_iterator inside the begin() method it work as variable type? -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

Ok, this is my code: #include <boost/multi_index_container.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/random_access_index.hpp> using namespace boost::multi_index; template<typename K,typename V> //K = Key, V = Value class Ordered_Map { private: struct mutable_pair { typedef K first_type; typedef V second_type; mutable_pair():first(K()),second(V()){} mutable_pair(const K& f,const V&s):first(f),second(s){} mutable_pair(const std::pair<K,V>& p):first(p.first),second(p.second){} K first; mutable V second; }; typedef multi_index_container< mutable_pair, indexed_by< random_access<>, ordered_unique<member<mutable_pair, K, &mutable_pair::first> > > > container1; container1 c; mutable_pair *r; public: V& operator[]( const K& key ) { r = new mutable_pair(key,V()); c.insert(c.end(),*r); return (*r).second; } typename container1::const_iterator cbegin() const { return c.cbegin(); } typename container1::const_iterator cend() const { return c.cend(); } }; int main() { Ordered_Map<std::string,int> myMap; myMap["Joe"] = 3; myMap["Lillo"] = 9; myMap["Mary"] = -3; for (auto i = myMap.cbegin(); i != myMap.cend(); ++i) std::cout << i->first << " - " << i->second << std::endl; std::cin.get(); return 0; } I now correctly get two iterators, but in this class don't work the assignment: my output is: Joe - 0 Lillo - 0 Mary - 0 -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

Now it work well!! Thanks! :) -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

Ok, now I want to make find() and erase() methods. In std::map, they return an iterator. Should I wrap the methods find() and erase(), to pass a const K& key, and return a container1:: const_iterator. is it right?

std::map::find and std::map::erase have several overloads: http://www.cplusplus.com/reference/stl/map/find/ http://www.cplusplus.com/reference/stl/map/erase/ And none of erase() overloads returns iterator. By the way, why don't you just inherit from multi_index_container and add [] operator? MIC itself already has STL-complient interace, so trying to rewrite it is hardly worth the effort. The following is your code, but with inheritance: #include <boost/multi_index_container.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/random_access_index.hpp> using namespace boost::multi_index; template<typename K,typename V> struct mutable_pair { typedef K first_type; typedef V second_type; mutable_pair():first(K()),second(V()){} mutable_pair(const K& f,const V&s):first(f),second(s){} mutable_pair(const std::pair<K,V>& p):first(p.first),second(p.second){} K first; mutable V second; }; template<typename K,typename V> class Ordered_Map : public multi_index_container< mutable_pair<K, V>, indexed_by< random_access<>, ordered_unique<member<mutable_pair<K,V>, K, &mutable_pair<K, V>::first> > >

{ public: V& operator[]( const K& key ) { insert(end(), mutable_pair<K, V>(key,V())); return get<1>().find(key)->second; } }; int main() { Ordered_Map<std::string,int> myMap; myMap["Joe"] = 3; myMap["Lillo"] = 9; myMap["Mary"] = -3; for (auto i = myMap.cbegin(); i != myMap.cend(); ++i) std::cout << i->first << " - " << i->second << std::endl; std::cin.get(); return 0; }

erase *does* return an iterator. The docs you're using are non-compliant, take a look for instance at

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf

In c++11, but not in c++03 http://www.tech-archive.net/Archive/VC/microsoft.public.vc.stl/2005-10/msg00...

Igor R. wrote

By the way, why don't you just inherit from multi_index_container and add [] operator? MIC itself already has STL-complient interace, so trying to rewrite it is hardly worth the effort. The following is your code, but with inheritance:

I have already written a lot of code that uses std::map. I would like to replace std::map with my class Ordered_Map without changing my code. This is possible his example? -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

Ok, I added at your code a wrap for find() and erase() methods and it work well. But the class don't compile on GCC 4.6.1 (Linux Ubuntu 11.10) instead work on MSVC 10... -- View this message in context: http://boost.2283326.n4.nabble.com/Container-with-insertion-order-tp4097717p... Sent from the Boost - Users mailing list archive at Nabble.com.

Another (last ?) question: how is possible simulate operator== for boost multi_index?

No need to simulate, comparison operators are already defined for MIC. You should only provide the relevant ops for your elements. In case of mutable_pair it would look like this: template<typename K,typename V> bool operator ==(const mutable_pair<K, V> &lhs, const mutable_pair<K, V> &rhs) { return lhs.first == rhs.first && lhs.second == rhs.second; }