January 2013 - Boost-users - lists.preview.boost.org

[boost 1.47] boost::interprocess::scoped_lock<boost::interprocess::named_recursive_mutex> and fork() (linux)
by Frank Bergemann 30 Jan '13

30 Jan '13

Hello, i have a problem with boost::interprocess::scoped_lock<boost::interprocess::named_recursive_mutex> and using that one recursively in a unix (linux) fork() process environment. I.e. I create the boost::interprocess::named_recursive_mutex in a root process, then fork a number of child processes and those synchronize each other via boost::interprocess::scoped_lock<boost::interprocess::named_recursive_mutex>. When i use the named_recursive_mutex in a recursive way, the 2nd instance of the scoped_lock<> of it hangs (for one of the children, the first one, which tries to do a recursive lock.) I didn't have an issue without recursions (before i just used named_mutex - but i need to protect an application level region on a higher level now). And i didn't have a problem with a test program that does NOT fork(), which i start #10 instances on linux in parallel, and which also uses nested scoped_lock<>'s for each of them. Does anybody know about issue of boost::interprocess::named_recursive_mutex or boost::interprocess::scoped_lock<boost::interprocess::named_recursive_mutex> for unix/linux fork()? Do i have to create my named_recursive_mutex AFTER the fork() for each process instance? (i use m_mutex = boost::interprocess::named_recursive_mutex(boost::interprocess::open_or_create, _shmId.c_str())). I read about this here: http://www.linuxprogrammingblog.com/threads-and-fork-think-twice-before-usi… It talks about need to call |pthread_mutex_init()|. Other pages seems to indicate, that there is only a problem, when i lock a mutex and then fork(), inheriting the lock to parent and child process. - many thanks! best regards, Frank

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how to create smart pointer array?
by young 30 Jan '13

30 Jan '13

What is wrong with: boost::scoped_ptr<byte> buff[10]; for(int i=0; i<10; i++) { int size = 2*i + 100; buff[i] = boost::scoped_ptr<byte>(new byte[size]); } ... -- View this message in context: http://boost.2283326.n4.nabble.com/how-to-create-smart-pointer-array-tp4642… Sent from the Boost - Users mailing list archive at Nabble.com.

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Simulating for loop iteration with iota
by Algocoders . 30 Jan '13

30 Jan '13

We have written a free chapter on "Simulating for loop iteration with iota" @ http://www.algocoders.com/sites/default/files/chapter1_c%2B%2B11algorithms_… HTH, Cheers, Algocoders http://www.algocoders.com/

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Building boost on Windows
by John Lilley 30 Jan '13

30 Jan '13

I am trying to figure out which libraries to build on Windows. I really only need "polygon" and "geometry". But what libraries these dependent on that also need to be built? I've tried to query which will be built and I'm not getting the expected results, for example: $ ./b2 --show-libraries --build-type=complete The following libraries require building: - chrono - context - date_time - exception - filesystem - graph - graph_parallel - iostreams - locale - math - mpi - program_options - python - random - regex - serialization - signals - system - test - thread - timer - wave Hmmmm... where is polygon and geometry? $ ./b2 --show-libraries --build-type=complete --with-geometry error: wrong library name 'geometry' in the --with-<library> option. Help please?

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Custom library names
by John Lilley 30 Jan '13

30 Jan '13

How does one build boost with custom library/DLL names? There are two reason for this -- Our software simultaneously runs 32-bit and 64-bit versions of itself, and things are easier if the library names reflect this (e.g. inject _x64_ and _x86_ into the names). -- If we have customized Boost in any way, we want to give it a unique name so that it cannot possibly be incorrectly loaded by other code. Thanks, John Lilley

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Mac OSX build options
by Tim Burgess 30 Jan '13

30 Jan '13

Hi, I'm trying to create an application for the Mac that is compatible with OSX 10.6 through 10.8, with both 32 and 64-bit support. How do I configure my Boost 1.50.0 to generate the appropriate binaries (I use serialisation, System and FileSystem), please? Best wishes. Tim Burgess Raised Bar Ltd. Tel: +44 (0)1827 719822 Web: http://www.raisedbar.net We can supply Roland and Avid products with specialist pre and post-sales support for visually-impaired users - just drop us a line for a quote. Don't forget to sign our on-line petition to lobby for improved access to music education and music technology at: http://www.raisedbar.net/petition.htm

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Build options on Mac OSX 10;.8
by Tim Burgess 30 Jan '13

30 Jan '13

Hi, I'm trying to create an application for the Mac that is compatible with OSX 10.6 through 10.8, with both 32 and 64-bit support. How do I configure my Boost 1.50.0 to generate the appropriate binaries (I use serialisation, System and FileSystem), please? Best wishes. Tim Burgess Raised Bar Ltd. Tel: +44 (0)1827 719822 Web: http://www.raisedbar.net We can supply Roland and Avid products with specialist pre and post-sales support for visually-impaired users - just drop us a line for a quote. Don't forget to sign our on-line petition to lobby for improved access to music education and music technology at: http://www.raisedbar.net/petition.htm

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C++11 Algorithms Book
by Algocoders . 30 Jan '13

30 Jan '13

The book "C++11 Algorithms Volume 1 : Using and Extending C++11, Boost and Beyond <http://www.algocoders.com/>" is published. *Table of Contents: http://www.algocoders.com/sites/default/files/toc_c%2B%2B11algorithms_vol1.… *<http://www.algocoders.com/sites/default/files/toc_c%2B%2B11algorithms_vol1.…> *Sample Chapter: http://www.algocoders.com/sites/default/files/chapter1_c%2B%2B11algorithms_… *<http://www.algocoders.com/sites/default/files/chapter1_c%2B%2B11algorithms_…> **<http://www.algocoders.com/sites/default/files/toc_c%2B%2B11algorithms_vol1.…> @Amazon : www.amazon.com/11-Algorithms-Volume-Extending-Beyond/dp/1482083396/<http://www.amazon.com/11-Algorithms-Volume-Extending-Beyond/dp/1482083396/> @Pothi.com (Indian Edition) : http://pothi.com/pothi/book/chandra-shekhar-kumar-c11-algorithms-volume-1<http://pothi.com/pothi/book/chandra-shekhar-kumar-c11-algorithms-volume-1> ** *Description* This book is vital to understand *algorithms* newly introduced in *C++11*with the help of practical examples illustrating *concepts*, *variations*, *customizations* and *correctness* with deep insight into internals with primary focus on *effective usage*. This book can be read by anyone having some experience in any higher level programming. Beginners in C++ will be able to learn basic concepts of C++11 algorithms with practical examples. Intermediate programmers in C++ will learn foundational aspect of C++11 algorithms in a pragmatic way. Expert programmers(aka C++ hackers) can enjoy interesting variations leading to future of C++11 algorithms(aka C++1y), Boost and beyond. This book(*Volume 1*) illustrates following algorithms: - *Numeric Algorithms* - Simulating for-loop iteration with iota - Customizing iota - Return Type of iota - Compile Time iota - Interesting variations of iota - *Quantifier Algorithms* - Universal Quantifier(*Predicate Satisfiability For All*) - Non-Existential Quantifier(*Predicate Satisfiability For None*) - Existential Quantifier(*Predicate Satisfiability For Some*) - Unique Quantifier(*Predicate Satisfiability For One*) - *Partition Algorithms* - Predicate Based Rearrangements - Partition Structure Validation - Bisection Algorithm - Group Partitions *Recommended Approach* Though this book can be read without reference to any other source, still we recommend our readers to keep a copy of the famous book *The C++ Standard Library, Second Edition : A Tutorial and Reference by Nicolai M. Josuttis* handy for gentle introduction to C++11 algorithms followed by diving into respective sections of our book for detailed information. In-depth treatment of foundational aspect of C++11 algorithms is covered in another book published by us Foundation of Algorithms in C++11, Volume 1(Revised Edition) : Using and Extending C++11, Boost and Beyond.<http://www.amazon.com/Foundation-Algorithms-Volume-Revised-Edition/dp/14819…> For more details, please visit the link : http://www.algocoders.com/article/books Enjoy Reading ! Cheers, Algocoders http://www.algocoders.com paranoids(a)algocoders.com

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[Fusion] Associative Sequence not so associative
by TONGARI 30 Jan '13

30 Jan '13

Hi, I'd expect the associative sequence could be constructed and assigned with another sequence in different order. But it doesn't work, the src sequence must in the same order as the dst sequence defined. E.g. map<pair<K1, int>, pair<K2, int> > cannot take make_map<K2, K1>(1, 2). This is a bit disappointing :-( Does I miss something?

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[Range][Iterator] iterate over an enumeration?
by John M. Dlugosz 29 Jan '13

29 Jan '13

I'd like to make it easy to do a BOOST_FOREACH for every value in an enumeration. I tried enum E { E_First, ⋯ , E_Last }; boost::counting_range(E_First, E_Last) but got compiler template barf. Can someone suggest a good way to do this?

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serialization
by Larry E. Ramey 29 Jan '13

29 Jan '13

I'm having some trouble with the portable_binary_archive. When we serialze our classes via the text archive, they go in and out just fine. My simple test cases work great with the portable_binary_archive. However, in our production code, I get an input stream error exception tossed when I try to read a class that has STL elements in it. I have tried reordering includes and making sure the boost/serialization/list.hpp or whatever comes in front of the STL list class. Heck, I even put all those includes as the very 1st line of my test program to make sure they were included 1st. I am at a loss as the exception really doesn't tell me much, and the only thing I could figure out is that reordering the includes did in fact fix a few of these exceptions. (I still have one left... very annoying) Any ideas? I'd post the code, but it is very intertwined and difficult to distill a clean example. (and my stupid trail test does in fact work) Larry

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regular expression to extract numbers
by Neil Sutton 29 Jan '13

29 Jan '13

Hi, I am new to using boost and am trying to learn basics so I can use regex features in my code. In my test program, I want a function to simply extract some numbers that follow after a certain string pattern and then to read those numbers into a vector. This is an outline of what i would like to do: // function definition #ifndef findnumbers.h #define findnumbers.h #include <string> #include <fstream> #include <vector> #include <boost/regex.hpp> #endif void findnumbers (ifstream& afile) { // assume file is opened in main - i have passed a reference boost::regex expression ( ....having trouble with this); // search for matches - there will be a fixed number of numbers e.g 10 std::string const_iterator start, end; start = afile.begin( ); end = afile.end( ); std::vector<int> results; boost::match_results<std::vector<int>::const_iterator> what; for(int count = 0; count !=10; count++) { boost::regex_search(start,end,what,expression) { //if a number is found place in the vector results.push_back(count); } So the first problem I have is defining a correct expression. The pattern has the format "sometext>NUMBERS<sometext" newline. The NUMBERS may be one or two digits combined and the pattern is repeated 10 times. I have searched the archives and tried to build something based on the examples I have read, but cannot seem to find a working solution. Can anyone help please in defining an expression? I do not need a solution to my function overall as I should be able to write it correctly once I know how to define the pattern. Kind regards

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[GIL] Why does 'get_color' take a tag object instead of its type only?
by TONGARI 29 Jan '13

29 Jan '13

Hi there, I'm curious of why gil::get_color(pixel, tag) is defined that way. Any need to take the tag value? If not, I'd prefer gil::get_color<Tag>(pixel) or just gil::get<Tag>(pixel) or even Tag::get(pixel). And if possible, I hope GIL would just make pixel a Fusion sequence. Thanks.

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stack_allocator
by Andrew Hundt 29 Jan '13

29 Jan '13

Is there some version of a stack allocator in the current 1.52 version of boost, perhaps in some detail namespace? I searched the source and the archives and the only one I could find disappeared after 1.39: http://www.boost.org/doc/libs/1_39_0/boost/signals2/detail/stack_allocator.… Cheers! Andrew Hundt

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Which Parallel Boost Graph Library should I use?
by Christopher Cowing-Zitron 29 Jan '13

29 Jan '13

Hello, There is more than one PBGL server, one hosted by Boost, and the other by the Open Systems Laboratory (OSL). It appears that each has code not included in the other, whether I look at the release or sandbox SVN versions of the library. I have three criteria as to which version(s) I should use, which are all equally important to my final choice. First, in general, which is more reliable, the Boost or the OSL version? Both Boost and the OSL know their stuff, so it's not that I question the authors' skill, but rather I don't know which version has received more testing and validation. Second, which is more up-to-date, both in terms of which is updated more frequently, and which is more algorithmically and mathematically current? While I know programmers do love their graph algorithms, I wonder if the actual computer scientists and mathematicians at the OSL are more on the cutting edge. Finally, whether I use the Boost or the OSL server, I am more interested in the sandbox version than the release, as the development version has a lot of good stuff which isn't present in the release. That being said, in my experience there is quite a bit of variability amongst sandbox libraries as to their readiness for use, and I am not sure whether either PBGL sandbox is functional. Note, if there is some feature in one of the sandboxes that I am quite interested in, but is not yet at production quality, I wouldn't mind fixing it up for the community. Answers to any or all of the above questions would be most appreciated. Have a good day, -- Chris

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narrowing conversion warning in boost's regex_traits_defaults.hpp when trying to initialize wregex object
by rsk82 28 Jan '13

28 Jan '13

The first line compiles ok. The second also produces working EXE, but in addition I get this large error: In file included from d:\boost/boost/regex/v4/regex_traits.hpp:35:0, from d:\boost/boost/regex/regex_traits.hpp:27, from d:\boost/boost/regex/v4/regex.hpp:39, from d:\boost/boost/regex.hpp:31, from test.cpp:4: d:\boost/boost/regex/v4/regex_traits_defaults.hpp: In instantiation of 'const charT* boost::re_detail::get_escape_R_string() [with charT = wchar_t]': d:\boost/boost/regex/v4/basic_regex_parser.hpp:804:54: required from 'bool boost::re_detail::basic_regex_parser<charT, traits>::parse_extended_escape() [with charT = wchar_t; traits = boost::regex_traits<wchar_t>]' d:\boost/boost/regex/v4/basic_regex_parser.hpp:308:36: required from 'bool boost::re_detail::basic_regex_parser<charT, traits>::parse_extended() [with charT = wchar_t; traits = boost::regex_traits<wchar_t>]' d:\boost/boost/regex/v4/basic_regex_parser.hpp:134:10: required from 'void boost::re_detail::basic_regex_parser<charT, traits>::parse(const charT*, const charT*, unsigned int) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>]' d:\boost/boost/regex/v4/basic_regex.hpp:215:7: required from 'void boost::re_detail::basic_regex_implementation<charT, traits>::assign(const charT*, const charT*, boost::re_detail::basic_regex_implementation<charT, traits>::flag_type) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>; boost::re_detail::basic_regex_implementation<charT, traits>::flag_type = unsigned int]' d:\boost/boost/regex/v4/basic_regex.hpp:661:4: required from 'boost::basic_regex<charT, traits>& boost::basic_regex<charT, traits>::do_assign(const charT*, const charT*, boost::basic_regex<charT, traits>::flag_type) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>; boost::basic_regex<charT, traits>::flag_type = unsigned int]' d:\boost/boost/regex/v4/basic_regex.hpp:382:33: required from 'boost::basic_regex<charT, traits>& boost::basic_regex<charT, traits>::assign(const charT*, const charT*, boost::basic_regex<charT, traits>::flag_type) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>; boost::basic_regex<charT, traits> = boost::basic_regex<wchar_t, boost::regex_traits<wchar_t> >; boost::basic_regex<charT, traits>::flag_type = unsigned int]' d:\boost/boost/regex/v4/basic_regex.hpp:367:48: required from 'boost::basic_regex<charT, traits>& boost::basic_regex<charT, traits>::assign(const charT*, boost::basic_regex<charT, traits>::flag_type) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>; boost::basic_regex<charT, traits> = boost::basic_regex<wchar_t, boost::regex_traits<wchar_t> >; boost::basic_regex<charT, traits>::flag_type = unsigned int]' d:\boost/boost/regex/v4/basic_regex.hpp:336:7: required from 'boost::basic_regex<charT, traits>::basic_regex(const charT*, boost::basic_regex<charT, traits>::flag_type) [with charT = wchar_t; traits = boost::regex_traits<wchar_t>; boost::basic_regex<charT, traits>::flag_type = unsigned int]' test.cpp:15:37: required from here d:\boost/boost/regex/v4/regex_traits_defaults.hpp:329:73: warning: narrowing conversion of ''\37777777605'' from 'char' to 'const wchar_t' inside { } [-Wnarrowing] d:\boost/boost/regex/v4/regex_traits_defaults.hpp:331:64: warning: narrowing conversion of ''\37777777605'' from 'char' to 'const wchar_t' inside { } [-Wnarrowing] code : #include <iostream> #include <boost/regex.hpp> int main() { boost::regex narrow_str_regex("a+"); boost::wregex wide_str_regex(L"a+"); } boost: http://sourceforge.net/projects/boost/files/boost/1.52.0/boost_1_52_0.7z compiler: http://sourceforge.net/projects/mingwbuilds/files/host-windows/releases/4.7… ( and I know that this is the bug: https://svn.boost.org/trac/boost/ticket/7263 ) so, any tricks to get around this (some compiler switches?, I dunno) ? Or can I just ignore this error ? (Yes I need regex matching on wide strings.) -- View this message in context: http://boost.2283326.n4.nabble.com/narrowing-conversion-warning-in-boost-s-… Sent from the Boost - Users mailing list archive at Nabble.com.

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[1.53.0] Beta release candidates 2 now available for testing
by Marshall Clow 28 Jan '13

28 Jan '13

Updated release candidate files for 1.53.0 beta 1 are available at http://boost.cowic.de/rc/ As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. This helps ensure the candidates build OK before we push them out to SourceForge. The files (and associated md5s) are: 579b680bf55f53cd6d50adc391cb6c23 *boost_1_53_0_beta1_rc2.tar.gz 02098bb6da0e9c10712ae63c16e6aeea *boost_1_53_0_beta1_rc2.tar.bz2 998e2616a66c50e5693f563afb899002 *boost_1_53_0_beta1_rc2.zip e4fde6a869a3e21f8751ba8b7fd471a8 *boost_1_53_0_beta1_rc2.7z There were three changes between rc1 and rc2: * Fixes for compilation errors in Boost.Serialization * Documentation updates for Boost.SmartPtr * Updates to Boost.Threads Thanks, --The release managers

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Re: [Boost-users] boost random in 2 dimensions
by Robert Patterson 28 Jan '13

28 Jan '13

@Gabriel >From your answer I understand that, the uniform distributed values are >generated seperately for x and y axis. Then both should be combined to >form a point over a plane. @Norbert i think this could do uniform distribution only over one co-ordinates. I am assuming you want to sample a point uniformly at random from a rectangular subset of the plane with the sides of the rectangle parallel to the axes. If not, the problem is a little more complex, but still soluble. However, for a square of size 1 Norbert is correct. The extension to a general rectangle is simple - just use two uniform_real_distributions (this will also give you floating point numbers as per your first post). Calls to two different uniform_real_distributions (or successive calls to one object) using the same engine object will give a point uniformly distributed in the rectangle. You are correct to point out that the individual coordinates are also uniformly distributed, but since they are independent they also yield a uniformly distributed point on the rectangle. Robert

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Assertion `invariant_()' failed. in boost multi index
by Sunil S Nandihalli 28 Jan '13

28 Jan '13

Hi Everybody, Boost multi index is a very nice library. But I have a situation where the invariant_() assertion fails. One of the indices is ordered based on a score which is computed with a function. The score of the same element can change when computed at different times. but however, the scores change, score decay over time, such that the previously computed order will always be right. While I don't know if this is the issue, I wanted to make sure that this kind of scoring functions does not cause a problem because of some caching that boost may be doing internally .. and also, the return value of the scoring function is a double which I can imagine can introduce some comparison issues. I am digging into the code to make sure that that is not the problem .. any pointers from the community is greatly appreciated. Thanks, Sunil.

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[spirit/qi] Error handler not called
by Szymon Gatner 28 Jan '13

28 Jan '13

Hi, I am trying to develop a JSON parser using spirit/qi so far it is not going bad but I am having serious problem with on_error and error handler. This is my code: namespace qi = boost::spirit::qi; namespace ascii = boost::spirit::ascii; namespace phoenix = boost::phoenix; template <typename Iterator> struct error_handler { template <typename, typename, typename, typename> struct result { typedef void type; }; void operator()(Iterator first, Iterator last, Iterator err_pos, const boost::spirit::info& info) const { std::cout << "never called"; } }; template <class Iterator> struct JsonGrammar : public qi::grammar<Iterator, Value(), ascii::space_type> { JsonGrammar() : JsonGrammar::base_type(json, "json"), error(error_handler<Iterator>()) { using qi::double_; using qi::lexeme; using qi::char_; using qi::int_; using qi::on_error; using qi::fail; using phoenix::construct; using phoenix::val; using namespace qi::labels; qi::on_error<qi::fail>(json, error(_1, _2, _3, _4)); string %= lexeme['"' >> +(char_ - '"') >> '"']; number = int_; member = string >> ':' >> value; array = '[' >> value % ',' >> ']'; object = '{' >> member >> *(',' >> member) >> '}'; value = array | object | number | string | qi::bool_ | "null"; json = array | object; json.name("json"); } phoenix::function<error_handler<Iterator> > const error; qi::rule<Iterator, std::string(), ascii::space_type> string; qi::rule<Iterator, int(), ascii::space_type> number; qi::rule<Iterator, Value(), ascii::space_type> json; qi::rule<Iterator, Array(), ascii::space_type> array; qi::rule<Iterator, Value(), ascii::space_type> value; qi::rule<Iterator, Object(), ascii::space_type> object; qi::rule<Iterator, std::pair<std::string, Value>(), ascii::space_type> member; }; now when i try to parse std::string json = "[1, 2, 3, 4, t]"; parising result is false. but error handelr is never called. What am I doing wrong? Regards, Simon -- Szymon Gatner The Lordz Games Studio www.thelordzgamesstudio.com

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boost random in 2 dimensions
by Danny 28 Jan '13

28 Jan '13

I am trying to use a boost random generator to make random points uniformly distributed over a plane surface. In the the following link, the code for doing it in a single dimension is available: http://stackoverflow.com/questions/2254909/boost-random-number-generator Here they use boost::uniform_int<> to generate numbers as int in a single dimension. But in my case I wish to generate numbers as float in two dimensions over a plane. Is there any distribution type available to use it in two dimensions? (I have seen boost::uniform_on_sphere, but it is for spherical surfaces.) Is it possible to to this using boost library? -- View this message in context: http://boost.2283326.n4.nabble.com/boost-random-in-2-dimensions-tp4641761.h… Sent from the Boost - Users mailing list archive at Nabble.com.

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[ICL] interval_map::find returns only const iterator
by CarlosRoVe 27 Jan '13

27 Jan '13

Hi, I am using boost v.1.49.0 and I have a question about ICL. We are building a system that stores information associated with time intervals. For this we are using the interval_map container, and every element that we insert in the map contains a right_open interval as the key, and an instance of the structure that holds the information as the value. Some of the features of the system are: 1. Minimum interval length is one second. 2. We have seen that the default behavior for interval_map is aggregate on overlap, but in our case we enforce that overlapping time intervals are not allowed. To achieve this, every time we try to insert an element we perform a check if the time interval overlaps with any of the existing intervals in the map, and if so, we ignore the element. 3. We should be able to modify the data associated with a time interval. We have seen that the find method of the interval_map container returns only a const iterator, but we would like to have a version of find that returns a non-const iterator as well. We want to be able to search for an element whose time interval contains a certain timestamp, and change its content. With the given requirements, find should return one element at most. For us it would be handy if ICL could also provide a version of find that returns a non-const iterator, but maybe I this would break the philosophy behind the design of ICL. We would be glad to hear ideas suggesting what we could do, or alternatives ways of dealing with other problem. Thank you very much. -- View this message in context: http://boost.2283326.n4.nabble.com/ICL-interval-map-find-returns-only-const… Sent from the Boost - Users mailing list archive at Nabble.com.

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boost::asio async
by huvcbo 26 Jan '13

26 Jan '13

Hello, I have a problem I hope I can get some help with. I use boost http-server3, I have a number of tcp/ip-client started and connects to a server, every 15 seconds sending tcp/ip-client a keepalive message. When an HTTP client connects get tcp/ip-client from a container, and from the http message, a new message must be sent via the tcp/ip-client, when the reply is received how can I return it to the http-session? When i send the message to the tcp/ip-client the http-session goes out of scope. Both http-server and tcp/ip-client use async_write and read. Appriciate any help. /Christer

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[accumulators] accumulator "adapters"?
by Pete Bartlett 25 Jan '13

25 Jan '13

Dear all, The accumulators library is a very nice way to get a set of statistics for a stream of numbers, doubles, say. Now let’s suppose I’m receiving a stream of boost::optional<double>s – e.g. let’s suppose I’m receiving simulation results and some simulations fail. It would be neat if I could somehow write and “adaptor accumulator” that took this stream of optionals and then, if they are not empty, pass them to an underlying accumulator. In rough terms: template<typename UnderlyingAccumulator , typename Sample > struct accumulator_adaptor { template<typename Args> void operator()( Args const& args) { Sample const& s = args[sample]; if( s ) { m_underlying_accumulator( *s ) ; //doesn’t compile UnderlyingAccumulator expects an Args, not a Sample } } private: UnderlyingAccumulator m_underlying_accumulator; }; (we might also define another accumulator that just counts the number of “bad” samples. Then by adding an appropriate feature adaptor, one could write something like accumulator_set< boost::optional<double> , tag::accumulator_adaptor< mean > , tag::bad_samples_count > For the data 1.0,2.0,boost::optional<double>(),4.0 This would return a mean of 7/3 and a bad_samples_count of 1. Is it possible for me to implement such an adaptor that would work for an arbitrary underlying accumulator? Thanks for your interest, Pete

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Does Boost have polymorphic functors as named-operators?
by TONGARI 25 Jan '13

25 Jan '13

Hi all, Is there something like -- functional::identity, functional::plus (not std::plus<T>), functional::assign...etc -- in Boost? I know I can use Phoenix _1, _1 + _2, _1 = _2..., but I'd expect something more basic. Sometimes I just need something like that but not willing to have all the ET things... Maybe they're just provided within Phoenix or Proto? Thanks for any help.

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