July 2008 - Boost-users - lists.boost.org

Is there a something in boost to facilitate binary buffer transformations into typed data structures/classes?
by Graham Reitz 28 Jul '08

28 Jul '08

I didn't see anything, but I may have missed something. Problem: Binary data is stored in a char buffer from a proprietary device: char* buffer = new char[6]; Data in buffer: [byte 1][byte 2][byte 3][byte 4][byte 5][byte 6] [---16 bit uint--][------------32 bit uint-------------] ...would like to convert to this in a C++'ish style using a boost facility if it exists: (or consider directing me somewhere else if it doesn't) struct // or class { boost::uint16_t first; boost::uint32_t second; } data; I would like to avoid a C-style way of doing this. This seems like something that would have been solved many times. thanks, graham

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Re: [Boost-users] XML library?
by Tan, Tom (Shanghai) 28 Jul '08

28 Jul '08

> On Sat, Jul 26, 2008 at 03:44:54PM +0200, Michiel Helvensteijn wrote: > > In the meantime, can anyone recommend another open source C++ XML library I > can use (with DOM parser)? > >http://xerces.apache.org/xerces-c/ POCO: http://www.appinf.com/poco/info/index.html

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German language Boost tutorial available
by Ruediger Berlich 27 Jul '08

27 Jul '08

Hi there, by the beginning of this year I have written a three-part tutorial on using Boost for a German IT publication ("iX"). The magazine has now made the articles publicly available on their web page, under the following URLs: http://www.heise.de/ix/artikel/2007/12/134/ http://www.heise.de/ix/artikel/2008/01/144/ http://www.heise.de/ix/artikel/2008/02/138/ Note that the articles still refer to Boost 1.33.x/1.34, so that a few things are not applicable anymore to the upcoming version 1.36 . Hopefully they are nevertheless usefull for a few people. Best Regards, Ruediger /*************************************************************************/ The Steinbuch Centre for Computing of Karlsruhe Institute of Technology (the Cooperation of Forschungszentrum Karlsruhe GmbH and Universitaet Karlsruhe TH) will run its annual GridKa School from September 8th to 12th, 2008. Please find further information at http://www.fzk.de/gks08 . /*************************************************************************/

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[Boost.thread] Exception handling strategy ?
by Ruediger Berlich 27 Jul '08

27 Jul '08

Hi there, is there a recommended strategy for exception (or more generally error-)handling with Boost.thread ? From what I can see it is not safe to throw an exception from within a thread, as it is not sure who catches it (or whether it gets caught at all). Best, Ruediger

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[ASIO] Correct way to reconnect a failed TCP connection
by Simon Pickles 27 Jul '08

27 Jul '08

Hello, I am having a little trouble getting my boost::ASIO TCP client to actually re-attempt a connected if the first attempt failed. With my server offline, the call to async_connect correctly times out. When I try the async_connect call a second time, it doesn't time out. I am running my io_service listener in a boost thread, and am not changing this between async_connect calls. However, my debugger (MSVC2005, boost 1.35) does show a thread exit at this time. I don't think its the relevant thread (at the second call to connect there is an extra thread running (the io_service I guess). Here's my two relevant files. Thanks very much for any pointers Simon // Network.cpp //-------------------- // CNetwork::Connect // ........ m_client = boost::shared_ptr<CASIOClient>( new CASIOClient( m_log, m_initXML, m_IO, this ) ); try { tcp::resolver resolver(*(m_IO.get())); tcp::resolver::query query( m_serverHost.c_str(), m_serverPort.c_str() ); tcp::resolver::iterator iterator = resolver.resolve(query); m_client->Connect(iterator); m_log->NET( "Looking for Server at %s:%s\n", m_serverHost.c_str(), m_serverPort.c_str() ); } catch (boost::system::error_code& e) { m_log->NET("%s\n", e.message().c_str() ); m_log->NET("Server not found?\n"); return -1; } catch (std::exception& e) { m_log->NET("Exception %s\n", e.what() ); return false; } // start the io service to listen for async ops if ( !m_listener ) m_listener = boost::shared_ptr<boost::thread>( new boost::thread(boost::bind(&boost::asio::io_service::run, m_IO.get()) ) ); //------------------------------------- // CASIOClient.cpp CASIOClient::CASIOClient( boost::shared_ptr<ILogInterface> log, boost::shared_ptr<IXMLInterface> xml, boost::shared_ptr<boost::asio::io_service> io, CNetwork* network ): m_IO(io), m_socket(*(io.get())), m_network(network) { m_log = log; m_initXML = xml; } void CASIOClient::Connect( tcp::resolver::iterator endpoint_iterator ) { tcp::endpoint endpoint = *endpoint_iterator; m_socket.async_connect( endpoint, boost::bind( &CASIOClient::HandleConnect, this, boost::asio::placeholders::error, ++endpoint_iterator)); m_connectionState = NETWORK_DISCONNECTED; } void CASIOClient::Close() { m_log->NET("Starting Close...\n"); m_IO->post(boost::bind(&CASIOClient::DoClose, this)); } ////////////////////////////////////////// void CASIOClient::HandleConnect( const boost::system::error_code& error, tcp::resolver::iterator endpoint_iterator) { if (!error) { m_log->NET("Connected: %s\n", error.message().c_str()); m_connectionState = NETWORK_CONNECTED; boost::asio::async_read_until( m_socket, m_rx, '@', // termination char boost::bind( &CASIOClient::HandleReadUntil, this, boost::asio::placeholders::error)); } else if (endpoint_iterator != tcp::resolver::iterator()) { m_log->NET("Connection unsuccessful: %s\n", error.message().c_str()); m_log->NET("Retrying\n"); tcp::endpoint endpoint = *endpoint_iterator; m_socket.async_connect( endpoint, boost::bind( &CASIOClient::HandleConnect, this, boost::asio::placeholders::error, ++endpoint_iterator)); } else { m_log->NET("Connect Error: %s\n", error.message().c_str()); DoClose(); } } void CASIOClient::HandleReadUntil(const boost::system::error_code& error) { if (!error) { std::istreambuf_iterator<char> iter(&m_rx); std::istreambuf_iterator<char> end; std::string read(iter, end); std::string clipMsg; while (read.length()) { int n = read.find("@"); clipMsg = read.substr( 0, n ); m_log->NET( "Message received: %s\n", clipMsg.c_str() ); m_network->QueueReceivedMessage( clipMsg ); read = read.substr( n+1, read.length()-n-1 ); } // start listening again boost::asio::async_read_until( m_socket, m_rx, '@', boost::bind( &CASIOClient::HandleReadUntil, this, boost::asio::placeholders::error)); } else { m_log->NET( "ReadUntil Error: %s\n", error.message().c_str() ); DoClose(); } } void CASIOClient::DoClose() { m_log->NET( "Closing ASIO\n" ); m_socket.close(); m_connectionState = NETWORK_FAILED; }

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[boost-users][StateChart] failure during termination
by Igor R 27 Jul '08

27 Jul '08

Hello, When trying to terminate an asynchronous_state_machine I get the error message: "Expression: list iterator not decrementable". This occures in state_machine::terminate_impl( state_base_type & theState, bool performFullExit ) in the line: else if ( currentStates_.begin() == --currentStatesEnd_ ), when trying to perform --currentStatesEnd_, as currentStatesEnd_== 0xcdcdcdcd (i.e. uninitialized). theState == outermost state of the machine. I believe the problem is actually somewhere in my own code, so my question is what it could be, according to the above symptom? I request the termination in the following way: struct ServerImpl { //.... shared_ptr<state_chart::fifo_scheduler<> > sessionScheduler_; state_chart::fifo_scheduler<>::processor_handle sessionProcessor_; ~ServerImpl() { // the scheduler resides in some pool, so it continues living after ~ServerImpl sessionScheduler_->terminate_processor(sessionProcessor_); } Thank you, Igor'.

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[Graph] Disjoint Sets and Incremental Components with VertexList=listS
by Pedro Teixeira 27 Jul '08

27 Jul '08

Hi all, I am quite new to boost and would appreciate a hint on the following matter. My doubt is related to what exactly does the API expects in terms of a ReadWriteProperty and currently I am not amble to figure it out how to instantiate a disjoint_set for a graph of type adjacency_list <setS, listS, undirectedS>. The example (to a vecS graph) shows: std::vector<size_type> rank(num_vertices(G)); std::vector<Vertex> parent(num_vertices(G)); typedef size_type* Rank; typedef Vertex* Parent; disjoint_sets<Rank, Parent> ds(&rank[0], &parent[0]); I just spent some time trying different combinations of map<Vertex, size_type> and map<Vertex, Vertex> but it does not work. Also tried boost::property_map<Graph, boost::vertex_predecessor_t>::type for parent, but it didn't work either. Can anyone shed some light? thanks! Pedro

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How do I push_back classes that disallow copy construction?
by Kevin Jenkins 26 Jul '08

26 Jul '08

How do I do this? Is there a way to make the boost::fusion vector hold references instead of copies? Or hold pointers? class DoNotCopyConstructMe { public: DoNotCopyConstructMe() {} private: DoNotCopyConstructMe(const DoNotCopyConstructMe &ref) {} }; DoNotCopyConstructMe var1,var2,var3,var4; boost::fusion::push_back(boost::fusion::make_vector(var1,var2,var3),var4); Error 1 error C2248: 'DoNotCopyConstructMe::DoNotCopyConstructMe' : cannot access private member declared in class 'DoNotCopyConstructMe' c:\boost_1_35_0\boost\fusion\view\single_view\single_view.hpp 38

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Re: [Boost-users] XML library?
by Andrej van der Zee 26 Jul '08

26 Jul '08

I would definitely prefer libxml2/libxml++ over xerces-c (its too big and awkward in usage - prepare to type alot). For simple and basic usage you could also use tinyxml/ticpp or rapidxml. And yes, its a pitty that Boost does not provide some basic XML parser/generator. In so many projects you end up needing just a simpel parser... Cheers, Andrej ----- Original Message ---- From: Michiel Helvensteijn <m.helvensteijn(a)gmail.com> To: boost-users(a)lists.boost.org Sent: Saturday, 26 July, 2008 10:44:54 PM Subject: [Boost-users] XML library? I was surprised not to find an XML parser/generator library in boost. Or is it hidden somewhere? Is it planned for a future release, perhaps? In the meantime, can anyone recommend another open source C++ XML library I can use (with DOM parser)? Thanks! -- Michiel Helvensteijn _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users __________________________________________________________ Not happy with your email address?. Get the one you really want - millions of new email addresses available now at Yahoo! http://uk.docs.yahoo.com/ymail/new.html

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(A dynamic) Singleton using weak_ptr and shared_ptr
by Martin Trappel 26 Jul '08

26 Jul '08

Hi all. I was faced with the requirement for a singleton class where the object has to be constructed dynamically and where I wanted to assure that the object is destructed automatically when no longer needed. A solution using shared_ptr and weak_ptr immediately came to mind and after a short google I found http://lists.boost.org/boost-users/2002/10/2014.php. However, if you have to assure that construction and destruction never overlap if you have multiple (sequential) initializations/destructions it gets a bit more complicated :) Well. Here follows what I have come up with and it seems to work pretty well. Any comments welcome. br, Martin Singleton using boost weak_ptr and shared_ptr --------------------------------------------- Requirement: Singleton that is constructed on first use (not on process start) and destroyed after the last "client-code" has finished with it. Note: It is therefore possible that more that one Singleton instances exist within a process's lifetime, BUT there must only be at most one Object active at any given time (Construction must not run before destruction has finished. Starting point: http://lists.boost.org/boost-users/2002/10/2014.php Problem of the simple solution: No protection against multiple initialization and against simultaneous deletion and construction. Solution: The construction and destruction of the singleton instance(s) has to be protected additionally. [CODE:dynamic_singleton.h] #pragma once ////////////////////////////////////////////////////////////////////// #include <boost/noncopyable.hpp> #include <boost/shared_ptr.hpp> #include <boost/scoped_ptr.hpp> ////////////////////////////////////////////////////////////////////// class dynamic_singleton : private boost::noncopyable { public: typedef boost::shared_ptr<dynamic_singleton> shared_t; static shared_t get_instance(); // Interface: void example(int cookie); // ... private: dynamic_singleton(); virtual ~dynamic_singleton(); struct impl; typedef boost::scoped_ptr<impl> impl_t; impl_t pimpl; struct deleter; friend struct deleter; }; [/CODE] [CODE:dynamic_singleton.cpp] #include "dynamic_singleton.h" #include <boost/weak_ptr.hpp> #include <boost/thread/recursive_mutex.hpp> #include <boost/thread.hpp> ////////////////////////////////////////////////////////////////////// #define MESG(msg) \ printf("%s\n", msg); \ /**/ ////////////////////////////////////////////////////////////////////// class atomic_bool : protected boost::noncopyable { public: atomic_bool() : b_(false) {} explicit atomic_bool(bool b) : b_(b) {} inline operator bool() const { boost::recursive_mutex::scoped_lock lock(sync_); return b_; } inline bool operator=(bool b) { boost::recursive_mutex::scoped_lock lock(sync_); b_ = b; return b_; } private: bool b_; mutable boost::recursive_mutex sync_; }; ////////////////////////////////////////////////////////////////////// struct dynamic_singleton::impl : private boost::noncopyable { impl() {} ~impl() {} static void start_construction() { boost::xtime spin_time; spin_time.sec = 1; while(the_object_exists) { boost::thread::sleep(spin_time); } } static void finish_construction() { assert(!the_object_exists); the_object_exists = true; } static void finish_destruction() { assert(the_object_exists); the_object_exists = false; } typedef boost::weak_ptr<dynamic_singleton> internal_shared_t; static internal_shared_t the_object; static boost::recursive_mutex sync_init; static atomic_bool the_object_exists; }; ////////////////////////////////////////////////////////////////////// dynamic_singleton::impl::internal_shared_t dynamic_singleton::impl::the_object; boost::recursive_mutex dynamic_singleton::impl::sync_init; atomic_bool dynamic_singleton::impl::the_object_exists; ////////////////////////////////////////////////////////////////////// struct dynamic_singleton::deleter { void operator() (dynamic_singleton* p) { assert(p); delete p; impl::finish_destruction(); } }; ////////////////////////////////////////////////////////////////////// dynamic_singleton::shared_t dynamic_singleton::get_instance() { // Syncronise Initialization: boost::recursive_mutex::scoped_lock lock(impl::sync_init); MESG(__FUNCTION__); // Acquire singleton pointer: shared_t object_ptr = impl::the_object.lock(); if(!object_ptr.use_count()) { impl::start_construction(); object_ptr.reset(new dynamic_singleton(), dynamic_singleton::deleter()); impl::the_object = object_ptr; impl::finish_construction(); } return object_ptr; } ////////////////////////////////////////////////////////////////////// dynamic_singleton::dynamic_singleton() { pimpl.reset(new impl()); MESG(__FUNCTION__); // For example open a unique system or process global resource printf(" >> Singleton opens the global resouce.\n"); } ////////////////////////////////////////////////////////////////////// dynamic_singleton::~dynamic_singleton() { MESG(__FUNCTION__); // For example close a unique system or process global resource printf(" << Singleton closes the global resouce.\n"); } ////////////////////////////////////////////////////////////////////// void dynamic_singleton::example(int cookie) { printf("%s(%d)\n", __FUNCTION__, cookie); } [/CODE] [CODE:main.cpp] #include "dynamic_singleton.h" #include <iostream> #include <boost/thread.hpp> struct singleton_user { explicit singleton_user(int num) : num_(num) { } void operator()() { using namespace std; printf("%d uses singleton ...\n", num_); dynamic_singleton::shared_t s = dynamic_singleton::get_instance(); s->example(num_); } int num_; }; int main(int argc, char* argv[]) { boost::thread t1( singleton_user(1) ); boost::thread t2( singleton_user(2) ); boost::thread t3( singleton_user(3) ); boost::thread t4( singleton_user(4) ); boost::thread t5( singleton_user(5) ); t1.join(); t2.join(); t3.join(); t4.join(); t5.join(); return 0; } [/CODE]

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