February 2009 - Boost-users

Re: [Boost-users] Remove edge
by Gianni Loiacono 16 Feb '09

16 Feb '09

Hi Michael, thanks for the answer. Can you write me an example for to use the remove_edge_if() function? I have read the docs on the site, but there isn't an example :( Thanks a lot Passa a Yahoo! Mail. La webmail che ti offre GRATIS spazio illimitato, antispam e messenger integrato. http://it.mail.yahoo.com/

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[Serialize] Problem creating boost::archive::text_iarchive
by Javier Sanz 16 Feb '09

16 Feb '09

Hello, I'm getting problems creating a boost::archive::text_iarchive with boosts version 1.35.0 and Visual C++ Studio 2005 (Version 8). When I do so I get a std::bad_alloc exception. The code is as follows: void Serialize::deserialize(std::ifstream &modelFile, CoreModel &c) { try { boost::archive::text_iarchive ia(modelFile); // This line throws the exception (I've seen it with the debugger) ia >> c; } catch (std::exception& ex) { // I catch the bad_alloc here } } And this code si called this way: ... for (...) { modelFile.open(model_name.c_str(), std::ios::binary); if (modelFile.is_open() == false) { // ... We deal with the error but it does not get into here } CoreModel model; Serialize::deserialize(modelFile, model); .... } With the debugger I have seen that the exception is thrown into the method text_iarchive_impl<Archive>::load. The method basic_text_iprimitive::load is not setting the size of the string and when the string resize is done the value is huge (is garbage actually) and it throws the std::bad_alloc. Digging into the mailing list I have seen a thread that explains the same problem: http://lists.boost.org/boost-users/2006/03/18032.php But the solution proposed there does not fit me (As far as I can see). /Thanks Francisco Javier Sanz Olviera

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Remove edge
by Gianni Loiacono 16 Feb '09

16 Feb '09

Hi all, I have defined my graph like this: typedef adjacency_list<vecS, vecS, undirectedS,NodoProperty, ArcoProperty> Graph2; And also: graph_traits < Graph2 >::edge_iterator ei, ei_end; Now, I want to delete all edges where the capacity is less than 10. Than I have write this code: for (tie(ei, ei_end) = edges(g); ei != ei_end; ++ei) { if (capacity2[*ei] < 10) { remove_edge(source(*ei,g),target(*ei,g),g); } } But the program after 2 cicles....it crashs :(....Why? Thanks a lot Passa a Yahoo! Mail. La webmail che ti offre GRATIS spazio illimitato, antispam e messenger integrato. http://it.mail.yahoo.com/

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boost::asio handler based on received data
by Abdo Haji-Ali 16 Feb '09

16 Feb '09

Greetings, A server that I'm communicating with sends two types of messages identified by an ID. The first message type is sent automatically on specific events. The second type is sent in response to commands. I want to provide an interface that notifies the user when events occur (asynchronously) and at the same time enable performing commands. My first implementation did this (pseudocode): // In initialization socket.async_receive(buffer, event_handler); // In send_command socket.send(command_buffer); socket.receive_async(response_buffer, user_response_handler); event_handler() { user_event_handler(); socket.async_receive(buffer, event_handler); } The problem here is that 'event_handler' might (or will?) receive the response message. An additional problem is that these messages have no specific order. In other words, the following sequence might occur: - Send command (A) - Send command (B) - Receive event notification - Receive response (A) - Receive response (B) A possible solution might be the following: // In initialization socket.async_receive(buffer, msg_handler); // In send_command socket.send(command_buffer); handlers_queue.enqueue(user_command_handler); socket.receive_async(response_buffer, msg_handler); // Line(3) msg_handler() { if (event) user_event_handler(); else handlers_queue.dequeue() (); // Call first user handler socket.async_receive(buffer, msg_handler); } I want to know if boost::asio provides a better way to solve this problem. I'm particularly interested if writing a custom io service can help me in this situation. Thanks you, -- Abdo Haji-Ali Programmer In|Framez

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[Lambda] Misplaced "const" causes runtime error?
by Paul Baker 16 Feb '09

16 Feb '09

Hi, The following program, as expected, outputs "1 1 1": #include <algorithm> #include <iostream> #include <vector> #include <boost/mem_fn.hpp> #include <boost/bind.hpp> #include <boost/lambda/bind.hpp> int main() { std::vector<std::pair<int, int> > pairs; pairs.push_back(std::make_pair(1, 1)); std::vector<int> result; std::transform(pairs.begin(), pairs.end(), std::back_inserter(result), boost::mem_fn(&std::pair<int, int>::first)); std::transform(pairs.begin(), pairs.end(), std::back_inserter(result), boost::bind(&std::pair<int, int>::first, _1)); std::transform(pairs.begin(), pairs.end(), std::back_inserter(result), boost::lambda::bind(&std::pair<int, int>::first, boost::lambda::_1)); std::cout << result[0] << ' ' << result[1] << ' ' << result[2]; } Changing "std::pair<int, int>" to "std::pair<const int, int>" on the line using boost::mem_fn or the line using boost::bind causes a compile-time error. However, performing the same change on the line using boost::lambda::bind leads to a successful compile - yet at run-time result[2] is set to a seemingly random value. This has been tested on Visual C++ 7.1 SP1, 8.0 SP1 and 9.0 SP1. Is this expected behaviour? I was expecting to see either a compile-time error or run-time success. Thanks

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[boost-users][signals]
by Germán Diago 16 Feb '09

16 Feb '09

Hello. I'm trying to implement a similar system to signals/slots found in qt, with connections at runtime. Now I need to know the argument types for a given signal, like boost::function<>::first_arg_type and so on. Is this possible, and how? thank you very much.

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[asio] read with transfer_at_least(300) return after 256 characters with no error
by tomasz jankowski 16 Feb '09

16 Feb '09

hello, how it is possible that size = boost::asio::read(socket_, boost::asio::buffer(serverReply_,300),boost::asio::transfer_at_least(300)); return with no error after reading 256? thanks, tom ---------------------------------------------------- Inżynierskie Targi Pracy 26.02.2009 http://klik.wp.pl/?adr=http%3A%2F%2Fwww.itp.BEST.krakow.pl&sid=643

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Importing namespaced templates
by Esben Mose Hansen 16 Feb '09

16 Feb '09

Hi, from the C++0x standard, 7.3.3 (5) I gather that it is not possible to write a using statement to import a templated function into the global namespace. E.g. #include <boost/units/quantity.hpp> using template<typename X, typename Y> boost::units::quantity_cast<X,Y>; will be malformed. The only alternatives I have been able to come up with are 1) Use boost::units::quantity_cast<X>(Y) which is a bit longwinded 2) Write a new quantity_cast in the global namespace, and forward it to the boost::units one. Is there a better way? (Sorry that this is only borderline a boost question) -- kind regards, Esben

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FindBoost.cmake
by Ruediger Berlich 16 Feb '09

16 Feb '09

Hi there, I'm using CMake as my build system -- not to build boost, but build my own project, which heavily depends on Boost. I habe in the past used the FindBoost.cmake macro to locate the most suitable Boost version. However, there does not seem to be a centrally maintained version of this file (I believe it originated from the KDE project ?), and I was wondering whether "anyone" in Boost was working on a replacement. After all, if CMake is considered as an alternative build system for Boost itself, allowing users to find the installed libraries would be the most logical step. Thanks and Best Regards, Ruediger

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Seeking writers to develop quarterly digests of Boost newsgroups
by Brian Wood 16 Feb '09

16 Feb '09

I'm planning to start an on line magazine called C++ Quarterly. *http://tinyurl.com/df6hn2 or **http://preview.tinyurl.com/df6hn2 * If you are interested in writing a quarterly digest of Boost Users and/or Boost Developers, please let me know. Alternatively, if you're interested in writing a non-digest article, I'd be happy to hear from you. Just to clarify something from the above link. I want to set things up so that advertisers send money directly to authors. Advertisers would send ads to us but money to authors. Brian Wood Ebenezer Enterprises www.webEbenezer.net <http://www.webebenezer.net/>

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