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

Limitations of BOOST_COROUTINES_V2 (pass by reference)
by Mueller-Roemer, Johannes Sebastian 09 Jul '14

09 Jul '14

Hi, aside from the fact that the new coroutines are - apparently intentionally - only unidirectional now (currently not much of an issue for me), I noticed that it is apparently no longer possible to yield values by reference as shown in the following example: #include <fstream> #include <string> #include <iostream> #include <boost/coroutine/all.hpp> using type = std::string; auto lines_from_file(char const * fname) -> boost::coroutines::coroutine<type>::pull_type { using namespace boost::coroutines; return coroutine<type>::pull_type{ [fname](coroutine<type>::push_type& yield) { std::string line; std::ifstream stream(fname); while(stream) std::getline(stream, line), yield(line); }, attributes(fpu_not_preserved) }; } int main(int, char**) { auto lines = lines_from_file("test.txt"); unsigned count = 0; for(auto& line : lines) std::cout << std::setw(4) << ++count << ": " << line << "\n"; } If one changes type to std::string const & the example no longer compiles. If I use the old BOOST_COROUTINES_V1 API boost::coroutines::coroutine<std::string const &()> works just fine. Is this limitation also intentional (why?) or is this an unintentional regression? Regards Johannes S. Mueller-Roemer -- Johannes S. Mueller-Roemer, MSc Wiss. Mitarbeiter - Interactive Engineering Technologies (IET) Fraunhofer-Institut für Graphische Datenverarbeitung IGD Fraunhoferstr. 5 | 64283 Darmstadt | Germany Tel +49 6151 155-606 | Fax +49 6151 155-139 johannes.mueller-roemer(a)igd.fraunhofer.de | www.igd.fraunhofer.de

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Boost.python with custom (Anaconda) python installation on Mac OSX
by Gianluca Meneghello 09 Jul '14

09 Jul '14

Dear all, Sorry for asking a probably basic question, I have been trying to use boost. python with Anaconda python (https://store.continuum.io/cshop/anaconda/) on Mac OSX without success. My current installation works with the standard OSX python, for example by running the test in boost_1_55_0/libs/python/example/quickstart using the following command: $/usr/bin/python test_extending.py where /usr/bin/python is the default OSX python. In contrast the command: $python test_extending.py where python is the custom Anaconda one fails with Trying: from extending import * Expecting nothing Fatal Python error: PyThreadState_Get: no current thread Abort trap: 6 I understand this is due to boost linking the wrong python --- i.e. the system python instead of the Anaconda one - -- but I cannot make up my mind on how to change this, despite the fact that the project-config.jam file created by bootstrap.sh seems to correctly point to the anaconda installation. Please let me know if I can provide more details. Thanks in advance for your help, gianluca

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[ptr_container] usage of auto_type
by Olaf Peter 09 Jul '14

09 Jul '14

Hello, I have the following code fragment: typedef boost::ptr_vector<T> vector_t; typedef message_vector_t::auto_type auto_t; .... vector_t v; { auto_t x(new T) // do something with x v.push_back(x.release()); // here rise my question } according http://www.boost.org/doc/libs/1_53_0/libs/ptr_container/doc/examples.html #6 Do I have to release x all the time? E.g. I want to use it in the loop, where at the end I have to push_back the value, where for my understanding x goes out of scope and hence is released automatically. After studying the header, there is no push_back for auto_type (which is static_move_ptr), but for std::auto_ptr (which is imo deprecated in C++11) and T (which converts it into an auto_type again). Is it correct or do I miss something?

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Wrapper to C++ Lists using Python Boost
by Kv Gopalkrishnan 09 Jul '14

09 Jul '14

Hi all I am relatively new to python boost and am trying to wrap a list of pairs using an iterator. In the Public section I have namespace sky{ class FindNextMask{ public: FindNextMask() {}; FindNextMask(int i):iter(i){} bool operator()(const pair<int,string>& p)const{ if (iter <= p.first) return true; else return false; } private: int iter; }; Then in another class say S class S { private: list<pair<int,string> > A; } I am unable to find a solution to this. Any help in this context would be appreciated. I know to write wrappers for pairs and vectors but I do not understand how to extend this to C++ lists and connect it with iterators and operators. class_<std::vector<std::pair<double, double> > >("VectorOfPairs") .def(vector_indexing_suite<std::vector<std::pair<double,double> > >()); class_<std::pair<double, double> >("DoublePair") // Wrapper for a pair only .def_readwrite("first", &std::pair<double, double>::first) .def_readwrite("second", &std::pair<double, double>::second); Kind Regards K.V.

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boost::function performance issues with C++11
by 饭桶 09 Jul '14

09 Jul '14

Hi, Does anyone know why -std=c++11 causes so much difference on boost::function? I was planed to understand if there any performance issues with big size of parameters. So I wrote a function that takes a vector as parameter, like func2 shows. I know it's better to use a pointer or reference as function parameter. I just want to evaluate the performance, so let's keep the vector as parameter. However, I found that it's quite slow when compiled with -std=c++11. In detail, it takes 173874 milliseconds with C++11, while it takes 3676 seconds without C++11. About 50 times slower!! How can that be? In my opinion, I thought boost::function should had the same performance with std::function. So I decided to try std::function in C++11 directly, Finally, it takes about 29233 milliseconds. That's till 8 times slows! Can anyone tell me what happend here? int func2(std::vector<int> i){ total += i.size(); return i.size(); } const int T = 1000000; s = boost::chrono::system_clock::now(); for (int i = 0; i < T; ++i) call(boost::bind(&func2, v)); e = boost::chrono::system_clock::now(); In case you need to know my enviorment, my OS is Arch, compiler is gcc 4.9.0, and optimizations are default. The execution time (ms) of three versions I tried: boost::function with C++11 : 173874 boost::function without C++11 : 3676 std::function in C++11 : 29233 Any thoughts are appreciated! Thanks, Athrun

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Determine if boost was compiled with c++11
by Chris Stankevitz 08 Jul '14

08 Jul '14

Hello, My project uses cmake, gcc with c++11 support, and boost compiled libraries. Apparently my project must use only boost libraries that were created with c++11. The consequences of not doing this are random crashes. Is there a way I can determine whether or not boost was compiled with a c++11 compiler? I would like to verify, at configure time, that a c++11 version of boost is being used. Thank you, Chris

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Re: [Boost-users] DateTime without serialization
by Macumber, Daniel 08 Jul '14

08 Jul '14

Thanks John, BOOST_SERIALIZATION_NO_LIB worked for me. I assume that some include I am using was inadvertently triggering the auto link with serialization even though I was not using that functionality. Thanks for the help! Dan -----Original Message----- Date: Mon, 07 Jul 2014 18:27:00 +0100 From: John Maddock <boost.regex(a)virgin.net> To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] DateTime without serialization Message-ID: <53BAD864.3090800(a)virgin.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed > Hello, I am using the DateTime library's to/from string > functionality but not the DateTime serialization > functionality. However, when I build my program boost > auto linking keeps trying to link against the serialization > library. Is there a way I can build and link against DateTime > without auto linking against serialization? I am using visual > studio 2013 and boost 1.55. Define BOOST_SERIALIZATION_NO_LIB to disable auto-linking of serialization. However... you should need to #include the date_time serialization code in order to use iostream output? John.

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Re: [Boost-users] boost::function performance issues with C++11
by Seeger, Steven D. (GSFC-444.0)[Embedded Flight Systems, Inc] 08 Jul '14

08 Jul '14

>Right, there are 1000 integers in the vector. If something, say STL, is bottleneck for boost::bind with C++ 11, it >should also be a bottleneck without C++11. And they should have the same performance. However, the fact shows >that C++11 mode has some additional overhead. I wanna figure that out. What if you try with just 1 integer? Does the difference in time stay proportionally the same? Steven

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[spirit] qi xml parser
by Michael Powell 07 Jul '14

07 Jul '14

Hello, I am building out a general use xml parser including attributes, arbitrary number of elements, and so on. So far so good, makes sense parsing names and so forth. However, how do you handle element content? Which could either be a string, or zero or more other elements (basically of the same rule as the enclosing element rule). It would seem you need a terminus, the empty element tag. In such a way that populates the parent (initial) element, and its children (of the same element kind). I'll be adapting structs to capture the results. I am also using a couple of helpful references, for instance: http://www.w3.org/TR/xml11/ http://stackoverflow.com/questions/9473843/boost-spirit-how-to-extend-xml-p… Also not sure quite how to capture the adapted parts at strategic rule opportunities. My domain model will look something like this, keeping it simple as possible: struct xattribute { std::string name; std::string value; }; typedef std::vector<xattribute> xattribute_vector; struct xelement; typedef std::vector<xelement> xelement_vector; struct xelement { std::string name; std::string content; xattribute_vector attributes; xelement_vector children; }; Thanks... Best regards, Michael Powell

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DateTime without serialization
by Macumber, Daniel 07 Jul '14

07 Jul '14

Hello, I am using the DateTime library's to/from string functionality but not the DateTime serialization functionality. However, when I build my program boost auto linking keeps trying to link against the serialization library. Is there a way I can build and link against DateTime without auto linking against serialization? I am using visual studio 2013 and boost 1.55. Thanks, Dan Sent with Good (www.good.com)

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