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BoostCon 2011: Registration deadline is Wednesday
by Dave Abrahams 08 Apr '11

08 Apr '11

The premier annual US C++ event, BoostCon, runs May 15-20, 2011 in beautiful Aspen, Colorado! See http://boostcon.boost.org for details. Hans Boehm, the father of C++ garbage collection and the C++0x threading model, headlines the fifth annual Boost Conference, with his keynote, "Threads and Shared Variables in C++0x." Other sessions about which which I'm personally excited: * Christopher Kohlhoff, the author of ASIO, is coming all the way from the "land down under" to present his library, slated for TR2. Also IPv6, and more! * Bartosz Milewski is going to talk about the relationship between C++ template metaprogramming and Haskell * Matt Calabrese presents his library implementation of the postponed C++0x concepts features Further topics include Unicode, lockfree programming, Boost.Units, compile-time graphs, database mapping, high-performance numerics, and... too many other good things to list. I'll be running a daily infrastructure workshop where we'll develop the frameworks for documentation, web services, build, test, packaging and distribution of C++ components, including ryppl. As usual, the best things about BoostCon are the people and the work that gets done between sessions. The pictures at http://boostcon.boost.org/photos/ give a pretty good sense of it, but there's truly no substitute for being there. If you haven't registered yet, fix that :-) at http://boostcon.boost.org/registration/. Your chance to save $100 expires on Wednesday. See you there! -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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Returning a ptr_vector of an abstract data type
by Jim Hodapp 08 Apr '11

08 Apr '11

I am using a ptr_vector<MyAbstractType> in a class called Container to store pointers to derived types inherited from MyAbstractType. In my Container class, I want to have a member function which returns the ptr_vector<MyAbstractType>. First, am I better off modelling this "getter" as an iterator over this ptr_vector or is it proper to return the ptr_vector itself? Right now, when trying to return the ptr_vector itself (a copy of it) I am getting an error: "/usr/include/boost/ptr_container/clone_allocator.hpp:34: error: cannot allocate an object of abstract type 'MyAbstractType' The function prototype for the getter is: ptr_vector<MyAbstractType> GetDestinations() const Is ptr_vector trying to make a copy of each MyAbstractType contained instead of copying the pointer value itself? This would indicate that I need a get() type method for ptr_vector like what a scoped_ptr has. Any recommendations on how to design this situation? Thanks, Jim

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mutable_buffer_1 Inquiry
by Carla Strembicke 08 Apr '11

08 Apr '11

Hi, I am using the asio::mutable_buffer_1. All I want to do is copy external data from buffer to the Buffer that the mutable_buffer_1 is assigned. I have been reading the documentation provided but am unable to make heads or tails as to how to get this simple operation done. Is this possible. Do I have to sue the stream buffer class and if so how? Thanks CONFIDENTIAL INFORMATION NOTICE: The information contained in this e-mail is privileged, confidential and intended solely for the use of the addressee named above. If the reader of this e-mail is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this e-mail is strictly prohibited. If you received this in error, please contact the sender and destroy all copies of this e-mail. Thank you.

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boost::multi_index
by ppatel＠archelongroup.com 08 Apr '11

08 Apr '11

Hello, I have a question regarding creating composite key/specifying length for arrays while using multi_index container based on following structure. struct TestStruct { char firstKey[50]; char secondKeyPart[3]; uint32_t thirdKeyPart; ......Some other information.... }; Do I really read to specify this lengths for character arrays? If yes, how do I do that while specifying key parts as below? typedef multi_index_container < TestStruct, indexed_by< //non-unique as some subscribers might have more than one number hashed_unique< composite_key< TestStruct, member<TestStruct, char*, &TestStruct::firstKeyPart>, member<TestStruct, char*, &TestStruct::secondKeyPart>, member<TestStruct, uint32_t, &TestStruct::thirdKeyPart>, > > > > TS; Thanks

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[MSM] Use events twice
by Sebastian Redl 08 Apr '11

08 Apr '11

Hi, I'm using MSM to implement a client for a simple network application. Basically, the server sends messages and the client changes state and responds to them as appropriate. One of these messages is THROW. THROW gets two arguments: an identifier (0-3) and a value. My client is supposed to sum up the values for consecutive THROW events with the same identifier, and on a change of identifier, store the sum somewhere and start over for the new identifier. So I have three states (id0, id1, id2 - there's some special handling, which is why they're separate states) and an event Throw(id, value). The transitions for idN are: Throw(my id, value) -> no switch, state.sum += value Throw(other id, value) -> switch to state of other id, reprocess event, storing the sum is handled by the exit action In other words, I want the next state to immediately handle the event as well, because there's a value there I need to store. The question is, how do I do this? Here's a sequence of events and actions that could occur: E1: [init] Throw(0, 4) -> [id0: ?] Entry [id0: ?] -> [id0: 0] [id0: 0] reprocess E1 -> [id0: 4] E2: [id0: 4] Throw(0, 8) -> [id0: 12] E3: [id0: 12] Throw(1, 7) -> [id1: ?] Exit [id0: 12] -> save 12 Entry [id1: ?] -> [id1: 0] [id1: 0] reprocess E3 -> [id1: 7] I hope I was clear enough. Sebastian

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[BGL] Writing an edge_iterator for add_edges in CSR graph
by Johan Oudinet 08 Apr '11

08 Apr '11

Hi, I'm trying to write an edge_iterator in order to load a CSR graph from a GraphViz by using the add_edges method. So far, I successfully write a edge_iterator so you can iterate on it and dereference it to get either a pair of vertex_descriptor or a edge label. However, if it try to use this iterator as arguments for the method add_edges of CSR graph, I got cryptic errors and I don't know how to solve them :-/ You can find the code that produce these errors here: http://tinyurl.com/csr-add-edges-error I will appreciate any help to understand what is going wrong or to write an edge_iterator that actually works with add_edges. Thanks. Regards, P.S.: I use Boost graph library 1.42 installed from Ubuntu 10.10 repositories. -- Johan () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments

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[MSM] problem compiling a functor-guard using a flag inside.
by Steckmann, Sven 08 Apr '11

08 Apr '11

Dear list, while developing I want to use functors for a guard. The state machine compiles well until I added a function call to the FSM which has a template parameter. Then I always got the following error message while compiling it with gcc 4.4.1. SubtractionControllerNew.cpp: In member function 'bool<unnamed>::player_::isCDLoaded::operator()(const EVT&, FSM&, SourceState&, TargetState&)': SubtractionControllerNew.cpp:175: error: expected primary-expression before '>' token SubtractionControllerNew.cpp:175: error: expected primary-expression before ')' token Does anybody know why this happens and how to circumvent it? Kind regards, Sven ---- Example from flags. I have modified the CDLoaded example to present the bug with the following lines: struct isCDLoaded { template <class EVT,class FSM,class SourceState,class TargetState> bool operator()(EVT const& ,FSM& fsm,SourceState& ,TargetState& ) { //return fsm.is_contained(); // this works well return fsm.is_flag_active<CDLoaded>(); // Line 175 } }; Row < Stopped , open_close , Open , none , isCDLoaded >, // Copyright 2010 Christophe Henry // henry UNDERSCORE christophe AT hotmail DOT com // This is an extended version of the state machine available in the boost::mpl library // Distributed under the same license as the original. // Copyright for the original version: // Copyright 2005 David Abrahams and Aleksey Gurtovoy. 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) #include <iostream> // back-end #include <boost/msm/back/state_machine.hpp> //front-end #include <boost/msm/front/state_machine_def.hpp> #include <boost/msm/front/functor_row.hpp> #include <boost/msm/front/euml/common.hpp> namespace msm = boost::msm; namespace mpl = boost::mpl; using namespace msm::front; namespace // Concrete FSM implementation { // events struct play {}; struct end_pause {}; struct stop {}; struct pause {}; struct open_close {}; struct NextSong {}; struct PreviousSong {}; // Flags. Allow information about a property of the current state struct PlayingPaused{}; struct CDLoaded {}; struct FirstSongPlaying {}; // A "complicated" event type that carries some data. struct cd_detected { cd_detected(std::string name) : name(name) {} std::string name; }; // front-end: define the FSM structure struct player_ : public msm::front::state_machine_def<player_> { // The list of FSM states struct Empty : public msm::front::state<> { // every (optional) entry/exit methods get the event passed. template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "entering: Empty" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "leaving: Empty" << std::endl;} }; struct Open : public msm::front::state<> { typedef mpl::vector1<CDLoaded> flag_list; template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "entering: Open" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "leaving: Open" << std::endl;} }; struct Stopped : public msm::front::state<> { // when stopped, the CD is loaded typedef mpl::vector1<CDLoaded> flag_list; template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "entering: Stopped" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "leaving: Stopped" << std::endl;} }; // the player state machine contains a state which is himself a state machine // as you see, no need to declare it anywhere so Playing can be developed separately // by another team in another module. For simplicity I just declare it inside player struct Playing_ : public msm::front::state_machine_def<Playing_> { // when playing, the CD is loaded and we are in either pause or playing (duh) typedef mpl::vector2<PlayingPaused,CDLoaded> flag_list; template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "entering: Playing" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "leaving: Playing" << std::endl;} // The list of FSM states struct Song1 : public msm::front::state<> { typedef mpl::vector1<FirstSongPlaying> flag_list; template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "starting: First song" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "finishing: First Song" << std::endl;} }; struct Song2 : public msm::front::state<> { template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "starting: Second song" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "finishing: Second Song" << std::endl;} }; struct Song3 : public msm::front::state<> { template <class Event,class FSM> void on_entry(Event const&,FSM& ) {std::cout << "starting: Third song" << std::endl;} template <class Event,class FSM> void on_exit(Event const&,FSM& ) {std::cout << "finishing: Third Song" << std::endl;} }; // the initial state. Must be defined typedef Song1 initial_state; // transition actions void start_next_song(NextSong const&) { std::cout << "Playing::start_next_song\n"; } void start_prev_song(PreviousSong const&) { std::cout << "Playing::start_prev_song\n"; } // guard conditions typedef Playing_ pl; // makes transition table cleaner // Transition table for Playing struct transition_table : mpl::vector4< // Start Event Next Action Guard // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Song1 , NextSong , Song2 , &pl::start_next_song >, a_row < Song2 , PreviousSong, Song1 , &pl::start_prev_song >, a_row < Song2 , NextSong , Song3 , &pl::start_next_song >, a_row < Song3 , PreviousSong, Song2 , &pl::start_prev_song > // +---------+-------------+---------+---------------------+--------------- -------+ > {}; // Replaces the default no-transition response. template <class FSM,class Event> void no_transition(Event const& e, FSM&,int state) { std::cout << "no transition from state " << state << " on event " << typeid(e).name() << std::endl; } }; // back-end typedef msm::back::state_machine<Playing_> Playing; // state not defining any entry or exit struct Paused : public msm::front::state<> { typedef mpl::vector2<PlayingPaused,CDLoaded> flag_list; }; // the initial state of the player SM. Must be defined typedef Empty initial_state; // transition actions void start_playback(play const&) { std::cout << "player::start_playback\n"; } void open_drawer(open_close const&) { std::cout << "player::open_drawer\n"; } void close_drawer(open_close const&) { std::cout << "player::close_drawer\n"; } void store_cd_info(cd_detected const& ) {std::cout << "player::store_cd_info\n";} void stop_playback(stop const&) { std::cout << "player::stop_playback\n"; } void pause_playback(pause const&) { std::cout << "player::pause_playback\n"; } void resume_playback(end_pause const&) { std::cout << "player::resume_playback\n"; } void stop_and_open(open_close const&) { std::cout << "player::stop_and_open\n"; } void stopped_again(stop const&){std::cout << "player::stopped_again\n";} // guard conditions struct isCDLoaded { template <class EVT,class FSM,class SourceState,class TargetState> bool operator()(EVT const& ,FSM& fsm,SourceState& ,TargetState& ) { //return fsm.is_contained(); return fsm.is_flag_active<CDLoaded>(); } }; typedef player_ p; // makes transition table cleaner // Transition table for player struct transition_table : mpl::vector< // Start Event Next Action Guard // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Stopped , play , Playing , &p::start_playback >, Row < Stopped , open_close , Open , none , isCDLoaded >, a_row < Stopped , stop , Stopped , &p::stopped_again >, // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Open , open_close , Empty , &p::close_drawer >, // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Empty , open_close , Open , &p::open_drawer >, a_row < Empty , cd_detected , Stopped , &p::store_cd_info >, // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Playing , stop , Stopped , &p::stop_playback >, a_row < Playing , pause , Paused , &p::pause_playback >, a_row < Playing , open_close , Open , &p::stop_and_open >, // +---------+-------------+---------+---------------------+--------------- -------+ a_row < Paused , end_pause , Playing , &p::resume_playback >, a_row < Paused , stop , Stopped , &p::stop_playback >, a_row < Paused , open_close , Open , &p::stop_and_open > // +---------+-------------+---------+---------------------+--------------- -------+ > {}; // Replaces the default no-transition response. template <class FSM,class Event> void no_transition(Event const& e, FSM&,int state) { std::cout << "no transition from state " << state << " on event " << typeid(e).name() << std::endl; } }; // Pick a back-end typedef msm::back::state_machine<player_> player; // // Testing utilities. // static char const* const state_names[] = { "Stopped", "Open", "Empty", "Playing", "Paused" }; void pstate(player const& p) { std::cout << " -> " << state_names[p.current_state()[0]] << std::endl; } void test() { player p; // needed to start the highest-level SM. This will call on_entry and mark the start of the SM p.start(); // tests some flags std::cout << "CDLoaded active:" << std::boolalpha << p.is_flag_active<CDLoaded>() << std::endl; //=> false (no CD yet) // go to Open, call on_exit on Empty, then action, then on_entry on Open p.process_event(open_close()); pstate(p); p.process_event(open_close()); pstate(p); p.process_event(cd_detected("louie, louie")); p.process_event(play()); // at this point, Play is active std::cout << "PlayingPaused active:" << std::boolalpha << p.is_flag_active<PlayingPaused>() << std::endl;//=> true std::cout << "FirstSong active:" << std::boolalpha << p.is_flag_active<FirstSongPlaying>() << std::endl;//=> true // make transition happen inside it. Player has no idea about this event but it's ok. p.process_event(NextSong());pstate(p); //2nd song active p.process_event(NextSong());pstate(p);//3rd song active p.process_event(PreviousSong());pstate(p);//2nd song active std::cout << "FirstSong active:" << std::boolalpha << p.is_flag_active<FirstSongPlaying>() << std::endl;//=> false std::cout << "PlayingPaused active:" << std::boolalpha << p.is_flag_active<PlayingPaused>() << std::endl;//=> true p.process_event(pause()); pstate(p); std::cout << "PlayingPaused active:" << std::boolalpha << p.is_flag_active<PlayingPaused>() << std::endl;//=> true // go back to Playing // as you see, it starts back from the original state p.process_event(end_pause()); pstate(p); p.process_event(pause()); pstate(p); p.process_event(stop()); pstate(p); std::cout << "PlayingPaused active:" << std::boolalpha << p.is_flag_active<PlayingPaused>() << std::endl;//=> false std::cout << "CDLoaded active:" << std::boolalpha << p.is_flag_active<CDLoaded>() << std::endl;//=> true // event leading to the same state p.process_event(stop()); pstate(p); } } int main() { test(); return 0; }

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boost::hash and string conflicts
by Erik Scorelle 07 Apr '11

07 Apr '11

Hi, We have been using boost hash to hash filenames, but have found with some of our user data that certain strings will produce the same hash code ( "0012g6" and "0012fu" for example). Is there a recommended way to predict or resolve these sorts of conflicts? Thanks in advance!

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[bjam] "Access is denied."
by Phil Bouchard 07 Apr '11

07 Apr '11

Greetings, I am trying to run bjam on Cygwin with the gcc toolset but I keep getting the following error messages: $ bjam toolset=gcc Access is denied. Access is denied. Access is denied. bjam works fine with msvc. Any help is appreciated. Thanks, -Phil

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I just spent most of the day learning about range and lambda.
by Jake Brownson 07 Apr '11

07 Apr '11

Great work guys, those libraries are awesome. Boost makes c++ into a pretty nice place to be. I've been using serialization, preprocessor, and shared_ptr for awhile now which are also pretty great too.

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