January 2009 - Boost-users - lists.preview.boost.org

Newbie: Partial Problem with link
by Paul Campbell 25 Jan '09

25 Jan '09

OK: method A in section 6 # SUCCESS g++ -I /usr/local/boost_1_36_0 regex_test.cpp -o regex \ /usr/local/boost_1_36_0/bin.v2/libs/regex/build/gcc-4.1.2/release/link-static/threading-multi/libboost_regex-gcc41-mt-1_36.a ./regex < jayne.txt > Will Success Spoil Rock Hunter? NG: method B in section 6 #FAILURE http://www.boost.org/doc/libs/1_37_0/more/getting_started/unix-variants.html #link-your-program-to-a-boost-library This is a snip from my make file do_regex_not_working: g++ -I /usr/local/boost_1_36_0 regex_test.cpp -o regex \ -L /usr/local/boost_1_36_0/bin.v2/libs/regex/build/gcc-4.1.2/release/threading-multi/ \ # don't worry about my mail wrap problem -lboost_regex-gcc41-mt-1_36 Execution: g++ -I /usr/local/boost_1_36_0 regex_test.cpp -o regex \ -L /usr/local/boost_1_36_0/bin.v2/libs/regex/build/gcc-4.1.2/release/threading-multi/ \ -lboost_regex-gcc41-mt-1_36 Error Message: /usr/bin/ld: cannot find -lboost_regex-gcc41-mt-1_36 collect2: ld returned 1 exit status make: *** [do_regex_not_working] Error 1 Can you see what could be in error ?

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Extending boost::function for mathematics?
by Jesse Perla 25 Jan '09

25 Jan '09

Steven: beautifully simple code on your previous post. I just fear that MPL is beyond the reach of mortals such as myself because I could never come up with that solution. If people are in the mood for this kind of stuff, let me post on a set of questions coming up in my libraries: 1) QUESTION 1: MANAGING DERIVATIVES FOR FUNCTIONS * I am doing a lot of work with functions that may have an associated derivative analytically or numerically determined. * This is the tip of the iceberg in associating a bunch of information with a mathematical function that all needs to be bundled. * I have been creating functors like the following: template <class ParamType> struct square{ typedef double result_type; //For adaptors double operator()(double x, const ParamType& params ) { return x*x;} double gradient(double x, const ParamType& params ){return 2 * x;} boost::function<double (double,const ParamType& params)> gradient(){return boost::bind(&square::gradient, *this, _1, _2)}; //I forget the exact notation for bind with member functions, but the idea is that it would return a boost::function. }; //Analytical derivative But I would also love the ability to use finitedifference or autodifferentiation algorithms for more complicated examples. Perhaps something like: struct square : finite_differences<int Order>{ double operator()(double x, const ParamType& params ) { return x*x;} }; //Analytical derivative * Ideally here, finite_differences<int Order> would be able to generate the derivative using order taylor series approx and the operator() to evaluate the function. Even here I am not sure the best way to organize it. 2) QUESTION 2: ADAPTATION AND USE LIKE BOOST::FUNCTION Now, lets say that there was something similar to boost::function but which had the "derivative" concept to call.gradient(...) to evaluate grad, or return a functor which is the gradient as another function.. Lets call it math_function for now. The behavior is things like the following: using lambda::_1; using lambda::_2; math_function<double (double)> mysquare(_1 * _1); //This will generate a math_function with the finite differences as its derivative. assert(mysquare(1) == 1); math_function<double (double)> mysquaregrad = mysquare.gradient(); //Gets the derivative, which was generated through finite differences. This could then be used to get the .gradient again for example. assert(mysquare.gradient(.1) == mysquaregrad(.1)); math_function<double (double, int)> myfunc(_1 + _2); math_function<double (double)> myboundfunc = bind(my_func, _1, 3); assert(myboundfunc.gradient(1.0) == 4.0); //And then to create one with an analytical derivative math_function<double (double)> mysquare(_1 * _1, 2 * _1); assert(mysquare.gradient(1.0) == 2.0); //evaluated through the analytical derivative. boost::function<double (double)> myboostsquare = mysquare.as_function(); //would be nice for interoperability... or something similar. //Then we can create a class such as polynomial which subclasses math_function polynomial_function<3> mypoly({{2, 3, 5}}); //Creates a third order polynomial. The operator() uses fancy algorithms for polynomial evaluation. math_function<double (double)> mypoly2 = mypoly; //Can adapt to a math_function for use in generic algorithms. math_function<double (double)> mypolygrad1 = mypoly.gradient(); polynomial_function<2> mypolygrad2 = mypoly.gradient(); //Maybe this is getting too fancy... 3) QUESTION 3: WHY DO I WANT ALL THIS STUFF? For the same reason that boost::function is so useful for functional programming. I am going to have a million permutations on this kind of pattern, am writing very generic algorithms, and would prefer not to have to write a superclass for every permutation of parameters. I want to be able to freely bind to it, easily use lambdas, and eventually want to add a bunch of other traits such as # of derivatives, range/domain, continuity, hessians, etc. that can be uniformly managed. 4) QUESTION 4: AM I INSANE? Is this at all possible or has something similar been done? It seems to me that it might be, but I am likely not be capable of doing it. Is piggybacking boost::function in some smart way here the best approach? Even if we can't subclass directly, can we copy the source code and intelligently add in a few extra functions, etc.?

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Re: [Boost-users] boost::interprocess::message_queue::timed_receive, bug or mistake? (Ion Gazta?aga)
by nacitar＠ubercpp.com 24 Jan '09

24 Jan '09

> From: Ion Gazta?aga <igaztanaga(a)gmail.com> > Subject: Re: [Boost-users] > boost::interprocess::message_queue::timed_receive, bug or mistake? > To: boost-users(a)lists.boost.org > Message-ID: <497ADAC1.9090204(a)gmail.com> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Use universal time instead of local time. Maybe this is not documented, > and maybe this might be severe limitation. I've seen that boost::thread > uses boost::system_time so maybe Interprocess should go this way. > > Regards, > > Ion > That makes sense, given my timezone, why it was acting as such. Works now, but you should definitely add that to the documentation. If you have knowledge of the boost's date/time features beforehand, it would seem obvious. But, as in my case, I only looked at boost's date/time features in order to get the timeout to work with interprocess, so I lacked the entire picture. A small footnote would have made it a lot clearer. Great library, thanks for the help.

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reversible_ptr_container question
by Archie14 24 Jan '09

24 Jan '09

I am using ptr_vector and tried to get last element from the vector using rbegin() - which apparently is not supported by ptr_vector unless I missed smth. After some search I found "reversible_ptr_container" in #include <boost/ptr_container/detail/reversible_ptr_container.hpp> I have my doubts if this is the one I should use because it is not easily found in the documentation and buried in the "details". The questions are: 1. For rbegin() relative to ptr_vector - should I employ reversible_ptr_containier? If yes then short example will be highly appreciated. 2. How to get last element from ptr_vector (not using --end())?

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Use of socket
by Johan Mazel 24 Jan '09

24 Jan '09

Hi I'm trying to create some code based on the code of the socket tutorial of the boost website. The code to create a UDP socket which will send datagram is the following one : boost::asio::io_service io_service; udp::resolver resolver(io_service); udp::resolver::query query(udp::v4(), argv[1], "daytime"); udp::endpoint receiver_endpoint = *resolver.resolve(query); udp::socket socket(io_service); socket.open(udp::v4()); But, to send something else than a Daytime request, I need to know what are the avalaible option to put instead of "daytime" in this line : udp::resolver::query query(udp::v4(), argv[1], "daytime"); Unfortunately and as far sa I know, the documentation is quite light about that. The only that I found is this one : http://www.boost.org/doc/libs/1_37_0/doc/html/boost_asio/reference/ip__basi… it is quite empty. Eventually, my goal is to use a specified port instead of a name of service. Thanks in advance for the help. Johan

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[asio] Reading datagram packets
by Chard 24 Jan '09

24 Jan '09

Is it possible to read the extra data that wasn't added to the buffer when a datagram is received ? E.g. given an initial receive instruction something like: char m_buf[10]; udp::endpoint m_endpoint; <--> udpSocket.async_receive_from(buffer(buf), m_endpoint, bind(ReadHandler, ...)); service.run(); If more than 10 characters were in the datagram packet, how can they be accessed? Calling other read methods (after processing in the ReadHandler) just appears to block (I guess it is looking for another packet). Surely I don't have to ensure the buffer is as large as I'll ever need it to be?

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event loop
by Jens Luedicke 24 Jan '09

24 Jan '09

Hello, is there something like a generic event loop library in boost? Jens -- Jens Luedicke web: http://perldude.de

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Re: [Boost-users] Tree library?
by joel falcou 24 Jan '09

24 Jan '09

Le Sam 24 janvier 2009 10:51, Thomas Klimpel a écrit : > Are you sure? The original poster seems to have a "rooted tree" in mind, > which is a special "directed acyclic graph" (DAG). I just looked at the > TOC of the boost::graph documentation, and the only DAG algorithm I could > find was "topological_sort". There is also the transitive_closure > algorithm, which could be used to compute the "partial order" relation of > the DAG, but I'm not sure whether this is really the appropriate way to > compute the "partial order" relation of a DAG (because the number of > edges could increase to O(V^2) and DAG's are not mentioned in the > corresponding documentation). Indeed, I wasn't thinking of the related algorithm. So yeah, boost::tree seems to lack then

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boost::interprocess::message_queue::timed_receive, bug or mistake?
by nacitar＠ubercpp.com 24 Jan '09

24 Jan '09

I'm using boost svn 50746 (latest at time of writing), on 32-bit Ubuntu Intrepid Ibex, with gcc/g++ 4.3.2 This is a simple test case showing that for some reason, message_queue::timed_receive is returning immediately for me, not throwing an exception, but just returning false which signifies that the timeout has been reached. The output of the program is as follows: Current time: 2009-Jan-23 17:40:29 After delay: 2009-Jan-23 17:40:34 Timeout at 2009-Jan-23 17:40:29 Note that the timeout occurs before it is supposed to, it returns instantly. Is this a bug, or am I doing something wrong? MINIMAL CODE: #include <iostream> #include <boost/interprocess/ipc/message_queue.hpp> #include <boost/date_time/posix_time/posix_time.hpp> // Link with boost_date_time int main(void) { char buf[1024]; std::size_t uSize; unsigned int priority; // Create a queue boost::interprocess::message_queue::remove("SOME_QUEUE"); boost::interprocess::message_queue mq(boost::interprocess::create_only,"SOME_QUEUE",1024,1024); // 5 second delay boost::posix_time::time_duration delay(boost::posix_time::seconds(5)); // current time boost::posix_time::ptime timeout = boost::posix_time::ptime(boost::posix_time::second_clock::local_time()); std::cout << "Current time: " << boost::posix_time::to_simple_string(timeout) << std::endl; timeout += delay; std::cout << "After delay: " << boost::posix_time::to_simple_string(timeout) << std::endl; if (mq.timed_receive(buf,sizeof(buf),uSize,priority,timeout)) { std::cout << "Got a message!" << std::endl; } else { std::cout << "Timeout at " << boost::posix_time::to_simple_string(boost::posix_time::ptime(boost::posix_time::second_clock::local_time()))<< std::endl; } return 0; }

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Preserving mtime with filesystem lib
by Brad Schick 24 Jan '09

24 Jan '09

Is there a portable way to use the boost filesystem library to copy files and preserve mtimes? I am writing a tool that moves media files around and mtime can be significant when other sources of metadata are absent (like exif, iptc, xmp). It would be a bummer to have to add platform specific code to do that. Thanks, -Brad

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