February 2009 - Boost-users

[Python] Expose c++ instances to python
by Germán Diago 04 Feb '09

04 Feb '09

Hello. I'm trying to embed python to an application. I did that with success and I'm using boost.python to make some bindings to my API. What I would like, is that the interpreter has access to my objects at runtime, namely, I don't want to create objects from python code but to use the c++ objects, created in my c++ application, from python (and I have wrappers for those in boost.python). I don't know how to achieve this. I just know how to wrap classes, but I have no idea how to expose instances. Any idea how to achieve this? I googled and found nothing clear. Thanks in advance.

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[serialization] Sending user data to serialize()?
by Robert Dailey 04 Feb '09

04 Feb '09

Hi, I have a complex case I'm trying to work with. I may be doing this completely wrong so if there is a better design for this I'm always open for that. However for now I'm going to assume my particular problem can be solved. There exists two classes: A and B. Class A is defined as such: class A { public: template< typename Archive > void load( Archive& archive, unsigned int ) { archive & m_listOfB; } private: std::vector<int> m_listOfInt; boost::ptr_vector<B> m_listOfB; }; And class B is defined roughly as: class B { public: template< typename Archive > void load( Archive& archive, unsigned int ) { // Code isn't important here } }; Here's the problem: For each B that is deserialized by A::load(), I need to pass in a reference to m_listOfInt. So, essentially the load() function in B would look something like this: void load( Archive& archive, unsigned int, std::vector<int>& listOfInt ) { } I was hoping boost.bind could be used somewhere, but I just don't see how. One way to solve the problem is to call B::load() explicitly with the extra parameter, but I don't think that's an appropriate solution. Any ideas on how to solve this? Or perhaps I'm trying to solve the wrong problem.

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[boost.asio] repeating a timer
by Sean Farrow 04 Feb '09

04 Feb '09

Hi: I've just been looking at the boost asio timers, I was wondering whetherthere is a repeat timer, so that my call back will be executed everytime the timer completes. This needs to execute more than once. Any help apreciated. Sean.

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Finding the n smallest items in a list
by Ruediger Berlich 04 Feb '09

04 Feb '09

Hi there, I'm searching for a method to find the n smallest numbers in a list of m >> n numbers. The n numbers need to be sorted. m will usually be in the range of 100-1000, n will be 5 or less. So far I'm simply sorting the entire vector, which I assume is not very efficient, as the other m-n items in the container can remain unsorted. Is there a function in Boost that can help me in this situation ? Best Regards, Ruediger

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[date_time] posix_time::time_duration::operator<< fails for hours>23
by Soren Dreijer 04 Feb '09

04 Feb '09

I'm creating a posix_time::time_duration object based on the minutes() helper function. If I specify a large value, such as 2000, I get a time_duration of 33:20:00. Take a look at the following piece of code, though: time_duration td = minutes(2000); cout << to_simple_string(td); // OK cout << td; // Fails with an assertion in VS2008 The latter call fails with the following assertion in strftime.c on line 658: _VALIDATE_RETURN( ( ( timeptr->tm_hour >=0 ) && ( timeptr->tm_hour <= 23 ) ), EINVAL, FALSE) Apparently, operator<< expands to _expandtime(), which doesn't allow values for the hour to be greater than 23. Is this intended behavior, or should I just always use to_simple_string() rather than the convenient operator<< ?

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[asio] how to handle sync_accept error to avoid server hang on?
by tomasz jankowski 04 Feb '09

04 Feb '09

hello, actualy I'm testing my server. I'm making new connections faster than server is able to handle it. because of it server quickly is getting from system errno 24 (Too many open files). because of chaining async operation in asio design async_accept handler like below lead to server hang on. void AnldServer::handle_accept(const boost::system::error_code& e) { if (!e) { new_connection_->start(); new_connection_.reset(new AnldConnection(io_service_, request_handler_)); acceptor_.async_accept(new_connection_->socket(), boost::bind(&AnldServer::handle_accept, this, boost::asio::placeholders::error)); }else{ NDSLOG_NOTICE_S() << "Accept error: " << e << "\n"; } } Since we are not starting a new accept operation the io_service will run out of work to do and the server will hang on (if it was daemonised) or exit(if not). ofcourse server in production environment couldn't behaves like this. server must can handle such situation. my question is: how to fix it? just start async_accept without creating new_connection in case of error? like this for example? void AnldServer::handle_accept(const boost::system::error_code& e) { if (!e) { new_connection_->start(); new_connection_.reset(new AnldConnection(io_service_, request_handler_)); acceptor_.async_accept(new_connection_->socket(), boost::bind(&AnldServer::handle_accept, this, boost::asio::placeholders::error)); }else{ NDSLOG_NOTICE_S() << "Accept error: " << e << "\n"; acceptor_.async_accept(new_connection_->socket(), boost::bind(&AnldServer::handle_accept, this, boost::asio::placeholders::error)); } } I have just tested above code - it seems to work fine. but maybe someone have beter solution> or maybe it is good idea to add sleep(5) before async_accept in case of error? thanks, tom ---------------------------------------------------- Twoja rodzina na bliscy.pl Zobacz: http://klik.wp.pl/?adr=http%3A%2F%2Fcorto.www.wp.pl%2Fas%2Fbliscy.html&sid=…

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What does sys_err = 3 mean? or where can I find out?
by Andrew Bond 04 Feb '09

04 Feb '09

I am using Boost filesystem and I am getting an error (sys_err = 3). Where can I find a human-readable explanation of this error? Are there text explanations that can be included in my app to better inform the end user what the erro means? Any help will be much appreciated. Andrew Bond

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Boost compatibility with Green Hills Integrity RTOS and Windows CE
by Vikas Goel 04 Feb '09

04 Feb '09

Hi, I am planning to use Boost libraries with Green Hills Integrity RTOS and Windows CE. Please let me know if there are any known issues (like build, compilation, etc) in running Boost on Green Hills Integrity RTOS and Win CE. Any comment regarding usage of Boost with any other RTOS is also welcome. Thanks & Regards, Vikas **************** CAUTION - Disclaimer ***************** This e-mail contains PRIVILEGED AND CONFIDENTIAL INFORMATION intended solely for the use of the addressee(s). If you are not the intended recipient, please notify the sender by e-mail and delete the original message. Further, you are not to copy, disclose, or distribute this e-mail or its contents to any other person and any such actions are unlawful. This e-mail may contain viruses. Infosys has taken every reasonable precaution to minimize this risk, but is not liable for any damage you may sustain as a result of any virus in this e-mail. You should carry out your own virus checks before opening the e-mail or attachment. Infosys reserves the right to monitor and review the content of all messages sent to or from this e-mail address. Messages sent to or from this e-mail address may be stored on the Infosys e-mail system. ***INFOSYS******** End of Disclaimer ********INFOSYS***

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[signals (thread safe)] Scope of slot_call_iterator (or how to implement deferred signals)
by Fabio Fracassi 04 Feb '09

04 Feb '09

Hi, I am currently trying to implement deferred signals using boost signals (well thread safe signals). I had the (crazy?) idea that it might be possible to hijack the combiner interface to do this. The design rational said that during the signal call the state (including the arguments that were passed) are cached for the combiner. So, what I tried to do was to copy and store the first and last iterater out of the combiner, to iterate over them at a later time, to call the slots. What I don't know is whether the slot_call_iterator (and the data it uses ) stays in scope after the signal call (i.e. signal...::operator() ) returns. Here is what I tried: #include <boost/signal.hpp> #include <boost/tr1/memory.hpp> #include <queue> struct signal_queue { signal_queue() : m_signals() {} template <typename InputIterator> void add_signal(InputIterator first, InputIterator last) { m_signals.push( std::tr1::shared_ptr<sig_iterator_range_placeholder>( new sig_iterator_range_holder<InputIterator>(first, last))); } bool process_one_signal() { if (!m_signals.empty()) { std::tr1::shared_ptr<sig_iterator_range_placeholder> sig = m_signals.front(); m_signals.pop(); sig->send(); return true; } return false; } private: struct sig_iterator_range_placeholder { virtual void send() = 0; }; template <typename InputIterator> struct sig_iterator_range_holder : sig_iterator_range_placeholder { sig_iterator_range_holder( InputIterator first, InputIterator last) : m_first( first ), m_last( last ) {} virtual void send () { while (m_first != m_last) { *m_first++; } return; } private: InputIterator m_first; InputIterator m_last; }; std::queue< std::tr1::shared_ptr<sig_iterator_range_placeholder> > m_signals; }; struct defered_send { typedef void result_type; template<typename InputIterator> void operator()(InputIterator first, InputIterator last) const { s_signalQueue.add_signal( first, last ); } static signal_queue s_signalQueue; }; signal_queue defered_send::s_signalQueue = signal_queue(); // Tests struct test_slots { void operator()() const { std::cout << "exec Slot()" << std::endl; } void operator()(int t1, int t2) const { std::cout << "exec Slot(" << t1 << ", " << t2 << ")" << std::endl; } }; int main () { boost::signal<void ( int, int ), defered_send> def_ii; test_slots test; def_ii.connect(test); std::cout << "Send Defered Signals ... " << std::endl; def_ii(42, 24); // <- Point 1 std::cout << "Entering 'event loop' ... " << std::endl; while ( defered_send::s_signalQueue.process_one_signal() ) {} std::cout << "Done." << std::endl << std::flush; return EXIT_SUCCESS; } The good news is that it doesn't crash, though I suspect that this is pure luck. After the slot call (Point 1) some things go out of scope (most notably the cache variable in slot_call_iterator). Now to make a long story short. Is what I am trying to do possible? If not should it? Or do I have to find another way to achive this? If so does someone have a hint? Regards Fabio

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Re: [Boost-users] Transferring files across a network.
by Andrew Maclean 03 Feb '09

03 Feb '09

To all those who helped, especially Rahul who very kindly made some sample code available and put me on the right track. I now have a client and a server that can handle multiple files being sent over the network. The files are attached for your interest. If anyone can improve them I really will welcome their comments. If there is a need, it is Ok to include them as examples in the ASIO documentation. I have no issues with this. Thanks once again to everyone who helped. Regards Andrew

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