May 2012 - Boost-users - lists.preview.boost.org

[Geometry] spatial linestring access along line
by Stephan Menzel 25 May '12

25 May '12

Hi all, before I begin, let me tell that geometry is not exactly my strong suite so please forgive my probably dumb question. I have started to work with boost geometry which, I find very neat, and assembled a line string. Now I basically need a method that gives me a point to a length value. Like when my linestring is 100 units long and I say give me the point at 3 I want the exact position of the point (coordinates) as if I were following the line for exactly 3 units. I have an approach that would allow me to implement this myself by following the segments (possibly after indexing them) but I have a feeling that one of those many functions provided by the library itself might do just that and I simply don't know it. If anyone knows if such is the case, would be nice to give me a heads up. Thanks, Stephan

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[multi_index] movable only types
by Szymon Gatner 25 May '12

25 May '12

Hi, with boost.move available are there any plans to make multi_index work with movable-only types? -- Szymon Gatner The Lordz Games Studio www.thelordzgamesstudio.com

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offlist - Re: [iterator] Problems with iterator_facade and const-qualification
by Neil Groves 24 May '12

24 May '12

On Sat, May 7, 2011 at 5:52 PM, Dave Abrahams <dave(a)boostpro.com> wrote: > On Fri, May 6, 2011 at 1:51 PM, Evan Driscoll <driscoll(a)cs.wisc.edu> > wrote: > > On 05/06/2011 11:59 AM, Jeff Flinn wrote: > >> > >> You might google any_iterator, and see how other authors have addressed > >> similar problems. > > > > Great! I tried to find someone who had done something similar, figuring I > > couldn't have been the first, but all the search terms I tried were too > > generic. > > > > Thanks, > > Evan > > You can find one in the ASL that's built on iterator_facade. > http://stlab.adobe.com/classadobe_1_1any__iterator.html > > The underlying Boost.Range implementation implements an any_iterator that I believe to be similar to the one in ASL in terms of functionality. I believe that the small-buffer optimization implementation is superior to forcing the definition of a closed-set of possible type as suggested in a TODO within the ASL documentation. During my performance testing I had considerably superior performance than the ASL implementation. I wondered if you disliked my implementation, or had any feedback. Additionally I wondered what you thought about moving the Boost.Range internal any_iterator implementation into Boost.Iterator. I can't honestly imagine a good use-case for using any_iterator in preference to any_range, hence I haven't suggested this previously. This could easily be due to my lack of imagination! Can you think of a time when using an any_iterator on any interface would be superior to using an any_range? Your opinions and guidance would be much appreciated. HTH, > > -- > Dave Abrahams > BoostPro Computing > http://www.boostpro.com Regards, Neil Groves

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Iterator concept checking
by McNamara, Nate 24 May '12

24 May '12

I'm trying to learn to use BOOST_CONCEPT_CHECK for custom iterators, ranges, and containers. I've built a simple linked list class with an iterator (and const_iterator) that, as far as I can tell, satisfies the forward traversal iterator requirements. However, g++ gives the following errors: concept.cpp:81: error: `*' cannot appear in a constant-expression concept.cpp:81: error: a call to a constructor cannot appear in a constant-expression concept.cpp:81: error: template argument 1 is invalid concept.cpp:81: error: template argument 1 is invalid concept.cpp:82: error: `*' cannot appear in a constant-expression concept.cpp:82: error: a call to a constructor cannot appear in a constant-expression concept.cpp:82: error: template argument 1 is invalid concept.cpp:82: error: template argument 1 is invalid concept.cpp:83: error: `*' cannot appear in a constant-expression concept.cpp:83: error: a call to a constructor cannot appear in a constant-expression concept.cpp:83: error: template argument 1 is invalid concept.cpp:83: error: template argument 1 is invalid concept.cpp:84: error: `*' cannot appear in a constant-expression concept.cpp:84: error: a call to a constructor cannot appear in a constant-expression concept.cpp:84: error: template argument 1 is invalid concept.cpp:84: error: template argument 1 is invalid Compiling with -E, lines 81-84 are as follows: typedef ::boost::concepts::detail::instantiate< &::boost::concepts::requirement_<void(*)(boost::concepts::ForwardTravers alIterator<iterator>)>::failed> boost_concept_check81; typedef ::boost::concepts::detail::instantiate< &::boost::concepts::requirement_<void(*)(boost::concepts::WritableIterat or<iterator>)>::failed> boost_concept_check82; typedef ::boost::concepts::detail::instantiate< &::boost::concepts::requirement_<void(*)(boost::concepts::ForwardTravers alIterator<const_iterator>)>::failed> boost_concept_check83; typedef ::boost::concepts::detail::instantiate< &::boost::concepts::requirement_<void(*)(boost::concepts::ReadableIterat or<const_iterator>)>::failed> boost_concept_check84; That tells me that, regardless of why g++ is having trouble, my iterator fails to satisfy the concept somehow. So I wrote some code (see my_naive_check, below) to try to figure out which requirement is failing, but my check code is missing the same thing as the iterator, because the check code runs fine. Any pointers much appreciated. // concept.cpp // What's wrong with the iterators? #include <cassert> #include <cstdlib> #include <iostream> #include <string> #include <boost/concept_check.hpp> #include <boost/iterator/iterator_concepts.hpp> #include <boost/iterator/iterator_facade.hpp> #include <boost/lambda/lambda.hpp> #include <boost/range/algorithm.hpp> template <typename T> class List { struct Node { Node(const T& value_, Node *next_): value(value_), next(next_) {} T value; Node *next; } *head; public: List(): head(0) {} ~List() { Node *node = head; while (node) { Node *tmp = node->next; delete node; node = tmp; } } void push_front(const T& value) { head = new Node(value, head); } class iterator: public boost::iterator_facade<iterator, T, boost::forward_traversal_tag> { public: iterator(): node(0) {} private: iterator(Node * const node_): node(node_) {} friend class List; friend class boost::iterator_core_access; T& dereference() const { return node->value; } bool equal(const iterator& rhs) const { return node == rhs.node; } void increment() { node = node->next; } Node *node; }; iterator begin() { return iterator(head); } iterator end() { return iterator(); } class const_iterator: public boost::iterator_facade<const_iterator, const T, boost::forward_traversal_tag> { public: const_iterator(): node(0) {} const_iterator(const iterator& old): node(old.node) {} private: friend class boost::iterator_core_access; const T& dereference() const { return node->value; } bool equal(const const_iterator& rhs) const { return node == rhs.node; } void increment() { node = node->next; } const Node *node; }; const_iterator begin() const { return const_iterator(head); } const_iterator end() const { return const_iterator(); } BOOST_CONCEPT_ASSERT((boost::concepts::ForwardTraversalIterator<iterator >)); BOOST_CONCEPT_ASSERT((boost::concepts::WritableIterator<iterator>)); BOOST_CONCEPT_ASSERT((boost::concepts::ForwardTraversalIterator<const_it erator>)); BOOST_CONCEPT_ASSERT((boost::concepts::ReadableIterator<const_iterator>) ); }; /* ForwardTraversalIterator must be SinglePassIterator IncrementableIterator Assignable Copy Constructible &r == &++r r++ *r++ == != difference_type DefaultConstructible iterator_traversal<X>::type => forward_traversal_tag */ void my_naive_check(List<std::string>& words) { typedef List<std::string>::iterator It; It it1 = words.end(); it1 = words.begin(); &it1 == &++it1; It it2 = it1++; std::string word = *it2++; assert(it1 == it2); assert(words.begin() != words.end()); It::difference_type distance = 0; It it3; boost::forward_traversal_tag tag = boost::iterator_traversal<It>::type(); } int main() { List<std::string> words; words.push_front("world"); words.push_front("Hello"); my_naive_check(words); boost::for_each(words, std::cout << boost::lambda::_1 << "\n"); return EXIT_SUCCESS; } ________________________________________ This E-Mail (including any attachments) may contain privileged or confidential information. 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boost::asio one connectio-per-thread
by Christer Borgqvist 24 May '12

24 May '12

Hello, is this a code appropriate? boost::asio::io_service io_service; tcp::acceptor a(io_service, tcp::endpoint(tcp::v4(),3080)); for (;;) { socket_ptr sock(new tcp::socket(io_service)); a.accept(*sock); emv_clientthread_ptr cli(new axf::server::server_socket(sock)); boost::thread t(boost::bind(&axf::server::server_socket::start, cli)); } appreciate any help. Christer

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[Chrono] Negative real time
by Wilfried Kirschenmann 23 May '12

23 May '12

Dear chrono maintainer team, Using the following example : int main(int argc, char **argv) { boost::chrono::process_real_cpu_clock::time_point start = boost::chrono::process_real_cpu_clock::now(); for ( long i = 0; i < 1000; ++i ) std::sqrt( 123.456L ); // burn some time Sleep(10000); //idle some time boost::chrono::process_real_cpu_clock::time_point end = boost::chrono::process_real_cpu_clock::now(); std::cout << end << std::endl; boost::chrono::process_real_cpu_clock::duration elapsed = (end - start); std::cout << "took real : " << elapsed << "nanoseconds\n"; return 0; } I obtain negative times. I run boost 1.49 win32 on Windows 7 x64 with Visual studio 2010. Studying the behavior of the timer, I think that the error is one of these : - process_real_cpu_clock::now() only stores the current time in a 32 bit integer instead of a 64 bit integer - time_points only prints the 32 lowest bits. I came to this conclusion by observing the results printed before they got negatives (printing in the loop with the sqrt): 2019000000 nanoseconds is the last value printed before getting negative. Is there any mistake in my way of using this chronometer ? Do you have a workaround ? Thank you for your help ! Wilfried K. ----- Cordialement, Wilfried Kirschenmann "An expert is a person who has made all the mistakes that can be made in a very narrow field."* *Niels Bohr - *Danish physicist (1885 - 1962)*

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boost::serialization "input stream error" in release-build (msvc2010)
by Jens Saathoff 23 May '12

23 May '12

Hi! I'm using boost::serialization to save a structure to a file and read from a file. My code works perfect in debug-build, but in release-build an exception is thrown. I'm using MSVC2010 to build the project on Windows 7 64-Bit-Machine. The code is the same. Who could help me out? You can find the code here: http://boost.codepad.org/8fp6XnC3 Thank you very much!!!!

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First attempt at using Boost::Test is a flop: the program ends with an exception related to std::string but I don't use any
by Ted Byers 23 May '12

23 May '12

Here is the full output from my program: $ ./decision.test.suite terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_S_construct NULL not valid Aborted (core dumped) Now, all the code in this program is focussed on number crunching, so none of it involves strings. I am guessing that I missed something in setting up a test suite. After including the headers for the function objects being tested (some of which are template classes) as well as headers for several boost libraries, I have the following: #define BOOST_TEST_MAIN decision_tests #include <boost/test/unit_test.hpp> #include <boost/test/floating_point_comparison.hpp> BOOST_AUTO_TEST_SUITE( test_decisions ) BOOST_AUTO_TEST_CASE( test_dist_moments ) { And I have a series of test cases that start the same way. After setting up the required data for each test, I use something like: BOOST_CHECK_CLOSE( Sm, 0.00000000000, 0.0001 ); or something like: BOOST_CHECK(ibll(x1,i) == true); Of course each test case ends with a closing '}' and the whole program ends with: BOOST_AUTO_TEST_SUITE_END() Now, I know I can write a suite of unit tests without using Boost::Test, but I was hoping I'd just missed something obvious. I don't even know where to look for the cause of this exception since none of the code I actually wrote that is involved in these tests makes any use at all of any strings. My guess is that I must have missed some macro required by the unit test framework that is required in order to ensure whatever string object is involved in this exception doesn't get a NULL value. Or maybe I missed a header. I really have no idea where to look for the cause of this problem. Any guidance on what to look for or what I may have missed, would be greatly appreciated. Cheers Ted

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boost::signals2::signal - is a "decimated" version available?
by Chris Stankevitz 22 May '12

22 May '12

Hi, I'm using boost::signals2::signal to notify a dialog when the state of an underlying object has changed. The signal is sometimes is generated at 100Hz. Other times it is generated at 1Hz. The dialog provides a "slot" for this signal that updates the controls on the screen. I'd like to limit the "slot rate" to 10Hz. By "slot rate" I mean the rate at which the slot receives notification from the signal. This will prevent the screen updates from happening faster than can be seen. Has this been done already? If not, I'm going to implement something like the pseudocode below. Currently I'm not sure how I to specify "arguments" nor how I am going to specify the function "SlotCallback". Thank you, Chris === Pseudocode: float MaxPeriod = 0.001; // 10Hz class SignalDecimator { public: void Register(signal Signal, slot Slot) { Signal.connect(&SignalDecimator::SlotCallback, this, _1, _2, _3, _4...); mSlot = Slot; } private: void SlotCallback(arguments Arguments) { if (TimeSinceLastCall() > MaxPeriod) { mSlot(Arguments); } else { mArguments = Arguments; if (!TimerIsRunning()) { StartTimer(MaxPeriod - TimeSinceLastCall()); } } } void TimerCallback() { mSlot(mArguments); } slot mSlot; timer mTimer; arguments mArguments; }

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Re: [Boost-users] asio - improving chat server example
by Marat Abrarov 22 May '12

22 May '12

Hi, John. > As you recall, I am using boost/Threads to execute io_service::run() to allow my server to have a > main-thread application loop. The use of threads have complicated my application design by giving me > problems to join the thread_group upon shutdown. > > I just had the thought, maybe I can tickle the io_service each frame of my main-thread loop instead of > using Threads? Is that the motivation for io_service::poll() ? Maybe using io_service.poll() will > allow me to avoid the need for threads, at least while I'm proving the concept. What do you think? I don't think asio::io_service::poll() can help you. The only solutions I can suggest I've described before. It isn't related to Asio - it is related to proactor pattern. > Maybe I can contribute a more interesting TCP server example if this works. :) Ideally, it would also > show clean shutdown when using threads to run the io_service, but I'm not there yet. I thought I've already done it :) > Also, I began looking at your code. Thank you for making it available. I'm a little worried it will > take me as long to learn your framework as it will to learn the Asio framework. It is not a framework. It is more like to be code snippets. Some parts are copies of Asio internals. Regards, Marat Abrarov.

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