June 2014 - Boost-users - lists.preview.boost.org

stack unwinding with boost::fcontext
by David Frank 20 Jun '14

20 Jun '14

Context - 1.53.0 beta1 Context - 1.53.0 beta1 Context Struct fcontext_t and related functions Each instance of fcontext_t represents a context (CPU registers and stack space). View on www.boost.org Preview by Yahoo I'm wondering if there is any example showing how to do stack unwinding as described at the bottom of the above link as quoted below: " Stack unwinding Sometimes it is necessary to unwind the stack of an unfinished context to destroy local stack variables so they can release allocated resources (RAII pattern). The user is responsible for this task. " Thanks, Frank

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[coroutine] await_emu example
by bbxiong 20 Jun '14

20 Jun '14

Hi, coroutine listers! The example is very awesome. but after reading though the source, i have a question: Is any limitation makes a push_coroutine must be caller and pull_coroutine must be the coro? This way, we have to yield out at the first line of coroutine function by calling caller(), just like the example showed: typedef coroutines::pull_coroutine<void> coro_pull; typedef coroutines::pull_coroutine<void> coro_push; auto asynchronous(F f) -> future<decltype(f())> { typedef promise<decltype(f())> CoroPromise; CoroPromise coro_promise; auto coro_future = coro_promise.get_future(); CurrentCoro current_coro = { make_shared<coro_pull>(std::bind([f](CoroPromise &coro_promise, coro_push &caller) { caller(); coro_stack.top().caller = &caller; coro_promise.set_value(f()); }, std::move(coro_promise), placeholders::_1); }; coro_stack.push(std::move(current_coro)); (*coro_stack.top().coro)(); coro_stack.pop(); return coro_future; } There is an extra call to caller() in coroutine function to jump out to prepare coro stack. Why not swap coro_pull and coro_push like this: auto asynchronous(F f) -> future<decltype(f())> { typedef promise<decltype(f())> CoroPromise; CoroPromise coro_promise; auto coro_future = coro_promise.get_future(); CurrentCoro current_coro = { make_shared<coro_push>(std::bind([f](CoroPromise &coro_promise, coro_pull &caller) { coro_stack.top().caller = &caller; coro_promise.set_value(f()); }, std::move(coro_promise), placeholders::_1); }; coro_stack.push(std::move(current_coro)); (*coro_stack.top().coro)(); coro_stack.pop(); return coro_future; } This still works on my machine, and has no extra "call to caller()", push_coroutine is not invoked until we explicitly run it (while pull_coroutine is invoked in constructor). So, my question is, s there any bad effects by using coroutines in this way? Thanks in advance!

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How to use vertex mapping parameter in copy_graph
by Christoph Czurda 19 Jun '14

19 Jun '14

Hello! I want to create a straight line drawing of a planar graph that is not maximal planar. So I want to follow the instructions in http://www.boost.org/doc/libs/1_55_0/libs/graph/doc/straight_line_drawing.h… : "If you want to draw a graph g, you can create a copy g' of g, store a mapping m of vertices in g' to vertices in g, triangulate g', and then send g' in as the input to chrobak_payne_straight_line_drawing. The drawing returned can then be applied to g using m to translate vertices from one graph to another." But I'm stuck at the point where I need to make a copy of the graph and store the vertex-to-vertex mapping between the two graphs. I'm not good enough at C++ to understand from the documentation at http://www.boost.org/doc/libs/1_55_0/libs/graph/doc/copy_graph.html how to provide or access the last parameter orig_to_copy(Orig2CopyMap c) If someone could fill in the missing code in this function, I would be most thankful! void doSomething(MyGraph_t& g){ MyGraph_t g_copy; copy_graph(g, g_copy, [...???...]); // here I would like to access the Orig2CopyMap which stores the mapping }

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Prominent Booster makes a big splash
by Robert Ramey 19 Jun '14

19 Jun '14

Notice that our own Matthias Troyer - important boost contributor made a big splash. http://www.theverge.com/2014/6/19/5824336/google-s-quantum-computer-just-fl… Robert Ramey -- View this message in context: http://boost.2283326.n4.nabble.com/Prominent-Booster-makes-a-big-splash-tp4… Sent from the Boost - Users mailing list archive at Nabble.com.

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[archive] binary archive to memory stream
by Michael Powell 19 Jun '14

19 Jun '14

Hello, I am wrapping my head around archive, specifically binary archive. I'd like to serialize a vector of objects in such a way, I need to capture intermediate vector buffers (literally, to vector of uint8_t) so that I can determine their sizes. After which point the parent object(s) can serialize to file using more conventional, built-in file streams and such. It seems that binary_oarchive is helpful, but still requires there be an ostream or streambuf in the mix. Which, as an adapter layer, while helpful, it still leaves the question of extending streambuf to work with ostream to vector<uint8_t> open. I've read some docs on vectors and streambuf, but they all seem to be geared towards a known-size vector, istream and such. I am interested in a vector that can be streamed to, will grow in size, etc. Some clues seem to hint at underflow, overflow type issues? Any helpful pointers how to go about doing this? Thanks... Best regards, Michael Powell

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[Python]compiling python library
by Miklós Tóth 19 Jun '14

19 Jun '14

Hi All, I want to embed python in my c++ code using boost.python library. As far as I understand I need python headers and libs. So my python27.lib is "incompatible". I want to compile it from code but I failed with mingw32. Could you give me some advice, or links to achieve my goal? I'm using gcc4.6.3 and qt 4.8.2 and boost 1.49 on windows 7. Thanks, Miklós

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Possible problem with property tree and ini files
by Tim Burgess 19 Jun '14

19 Jun '14

Hi, I make the following call in my application, based on Boost 1.55.0: property_tree::ini_parser::read_ini(IniFile.GetFullPath().ToStdString(), IniTree); This works fine for .ini files up to 64kb, but throws an exception for larger files. Is this a known limitation and, if so, can anybody suggest an alternative that could cope with larger files, please? Best wishes. Tim Burgess

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Splitting string at whitespace
by Florian Lindner 17 Jun '14

17 Jun '14

Hello, for some time now I've been trying to split a given string at whitespaces: "A B C" -> "A", "B", "C". I want to use boost/algorithm/string #include "boost/algorithm/string/split.hpp" #include "boost/algorithm/string/compare.hpp" std::vector<std::string> tokenize(const std::string& text ) { std::vector<std::string> tokens; boost::algorithm::split(tokens, text, boost::algorithm::is_equal(" ")); return tokens; } but compilation on gcc 4.9.0 / boost 1.55.0 just gives: test.cpp: In function 'std::vector<std::basic_string<char> > tokenize(const string&)': test.cpp:40:71: error: no matching function for call to 'boost::algorithm::is_equal::is_equal(const char [2])' boost::algorithm::split(tokens, text, boost::algorithm::is_equal(" ")); ^ test.cpp:40:71: note: candidates are: In file included from /usr/include/boost/algorithm/string/finder.hpp:24:0, from /usr/include/boost/algorithm/string/split.hpp:17, from test.cpp:7: /usr/include/boost/algorithm/string/compare.hpp:34:16: note: boost::algorithm::is_equal::is_equal() struct is_equal ^ /usr/include/boost/algorithm/string/compare.hpp:34:16: note: candidate expects 0 arguments, 1 provided /usr/include/boost/algorithm/string/compare.hpp:34:16: note: boost::algorithm::is_equal::is_equal(const boost::algorithm::is_equal&) /usr/include/boost/algorithm/string/compare.hpp:34:16: note: no known conversion for argument 1 from 'const char [2]' to 'const boost::algorithm::is_equal&' What is wrong there? Thanks, Florian

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Boost Voronoi: Automate creation of graph for indoor navigation
by Stadin, Benjamin 16 Jun '14

16 Jun '14

Hi all, I’m provided with geometry data for buildings. The data contains info about the „feature“ type of a geometry (floor, room, stairway, elevator). Now I need to automate the creation of an indoor routing graph (room-to-room navigation) to minimize manual works later on. This is not for a robot scenario – the line parts will be shown on a map application. Therefore it should also look good (routing edges should be centered etc). This is new land for me and I’ll will be grateful for advise how to achieve this. My initial thought is that Voronoi may be helpful. But this alone will probably not be sufficient. Any pointers and examples welcome. Thanks Ben

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[numeric conversation] behavior on std::numeric_limits<double>::max() + eps with numeric_cast
by Olaf Peter 16 Jun '14

16 Jun '14

Hello, at this time I play with numeric_cast and struggle with this: first: double z = std::numeric_limits<double>::max(); z += 2*std::numeric_limits<double>::epsilon(); // doesn't matter if 1*eps std::cout << z << std::endl; std::cout << boost::numeric_cast<double>(z) << '\n'; I would expect that an exception is thrown which isn't, the output is 1.79769e+308 1.79769e+308 and as second: If I write my onw UDT as shown in the tutorial like: namespace my { enum range_check_result { cNonFinite = 0, cInRange = 1, cNegOverflow = 2, cPosOverflow = 3 } ; //! Define a custom range checker template<typename Traits, typename OverFlowHandler> struct range_checker { typedef typename Traits::argument_type argument_type; typedef typename Traits::source_type S; typedef typename Traits::target_type T; //! Check range of integral types. static range_check_result out_of_range(argument_type value) { if(!std::isfinite(value.to_builtin())) // Neither infinity nor NaN. return cNonFinite; else if(value > boost::numeric::bounds<T>::highest()) return cPosOverflow; else if(value < boost::numeric::bounds<T>::lowest()) return cNegOverflow; else return cInRange; } static void validate_range(argument_type value) { BOOST_STATIC_ASSERT(std::numeric_limits<T>::is_bounded); OverFlowHandler()(out_of_range(value)); } }; .... struct bad_numeric_cast : virtual boost::exception, virtual std::bad_cast { ... }; struct rounding_error : virtual boost::exception, std::domain_error { rounding_error() : std::domain_error("NaN or Infinity") {} // XXX Better solution? virtual const char * what() const throw() { return "bad numeric conversion: can not be represented in the target integer type"; } }; struct negative_overflow : virtual bad_numeric_cast { .... }; struct positive_overflow : virtual bad_numeric_cast { .... }; struct overflow_handler { void operator()(range_check_result result) { if(result == cNonFinite) BOOST_THROW_EXCEPTION(rounding_error()); else if(result == cNegOverflow) BOOST_THROW_EXCEPTION(negative_overflow()); else if(result == cPosOverflow) BOOST_THROW_EXCEPTION(positive_overflow()); } }; it doesn't change the result - is this the right way? Thanks, Olaf

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