November 2010 - Boost-users

Re: [Boost-users] MPI build problems in Fedora 14 x64
by Manish Kumar 15 Nov '10

15 Nov '10

Have u installed MPI or open MPI ? I think u need to install it first. Regards On Mon, Nov 15, 2010 at 8:08 PM, <> wrote: > Hello, > > I'm building boost libraries in a Fedora 14 x64. > In this Linux distribution, mpi.h is located in /usr/include/openmpi-x86_64 > and the build process complains about not finding mpi.h. > How can I configure the build process so that it can find mpi.h? > Thansk, > > Juan Farré > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users > -- Manish Gupta Bioinformatics Software Developer Synamatix Sdn Bhd. Kulalumpur, Malaysia

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[netlib] 0.8-beta now available!
by Dean Michael Berris 15 Nov '10

15 Nov '10

Hi Everyone, advanced apologies for cross-posting. I've just tagged and uploaded archives of the cpp-netlib 0.8-beta which features: * An asynchronous server template, allowing for server-side streaming of data, asynchronous writing and reading facilities for server-side handlers, and a thread pool implementation that's temporarily using Boost.Asio's io_service for application-specific asynchronous handlers to run from. * A `ready(...)` wrapper to check for whether an asynchronous client's response is ready. The documentation has also been updated to feature a brand-new reference manual detailing the implementation, caveats, and public API of the HTTP client and server templates. You can go ahead and download the 0.8-beta and report issues you find either directly to me or through the mailing lists (Boost.User, Boost.Devel, and the cpp-netlib developers mailing lists). The target release for 0.8 will be this Friday, November 19, 2010. As usual, you can download the 0.8-beta package from GitHub at: https://github.com/cpp-netlib/cpp-netlib/downloads You can also check out the documentation for 0.8-beta at: http://cpp-netlib.github.com/0.8-beta Thanks everyone and I look forward to most appreciated feedback! -- Dean Michael Berris deanberris.com

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asio UDP async receive question - seems to lose packets?
by Ákos Maróy 15 Nov '10

15 Nov '10

Hi, I have a question about boost asio UDP async receive. For me, it seems to silently not receive packets, even on localhost. I have a small sample here: http://pastebin.com/NnbK1T7G , which is based on one of the asio examples. the sample code is quite simple: - it allows sync sending of messages (strings) - it allows async reception of such messages - it will put each received message into a vector, which is guarded by a mutex - another thread will process messages from this vector on a regular basis, which processing is also guarded by a mutex. if I compile & run the sample, I get: ./async_asio b sent 20000 messages a received 1981 messages which is a profound loss of packets. as seen in the sample, after the receive handler is called, the recieved message is copied over, and socket::async_receive_from() is called ASAP. I don't see what else would need to be done to have all messages received. If I remove the processing of messages in threa_func(), the results are markedly better: ./async_asio b sent 20000 messages a received 19963 messages increasing the sleeping time at the end does no good - it seems the messages were lost already. I wonder what the proper pattern is to receive messages, store them, and process them in an async manner? Akos

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Re: [Boost-users] Boost.Random multithreading
by Heiko Bauke 15 Nov '10

15 Nov '10

Dear Juan Antonio, On Sun, 14 Nov 2010 16:03:12 +0100 Juan Antonio Farré Basurte <jafb(a)tinet.org> wrote: > Are random number generators thread safe? Can I use a random number > generator by multiple threads without explicit locking? > > I guess the answer is no... Then I wonder if every thread could use a > different instance of the same random number generator without > interference between the different generators. you might consider to use the TRNG library [1] for multithreaded Monte Carlo. It is very similar to Boost random but has some special support for parallel random number generation. Read the TRNG documentation [2] for details. Regards, Heiko [1] http://trng.berlios.de/ [2] http://trng.berlios.de/trng.pdf -- -- Wer lügt, hat die Wahrheit immerhin gedacht. -- (Oliver Hassencamp, dt. Schriftsteller, 1921-1987) -- Number Crunch Blog @ http://numbercrunch.de -- Heiko Bauke @ http://www.mpi-hd.mpg.de/personalhomes/bauke

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[multi_index] How to use a class instead of a struct with the boost:multi_index_container? (addendum)
by jamaj 15 Nov '10

15 Nov '10

Hi All, Since I posted the previous message, I made some experiments. First, I changed the employee from struct to class: From struct employee { int id; std::string name; int age; employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){} friend std::ostream& operator<<(std::ostream& os,const employee& e) { os<<e.id<<" "<<e.name<<" "<<e.age<<std::endl; return os; } }; to class employee { int id; std::string name; int age; employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){} friend std::ostream& operator<<(std::ostream& os,const employee& e) { os<<e.id<<" "<<e.name<<" "<<e.age<<std::endl; return os; } }; I got some errors /home/jamaj/src/wxTestes/multiindexsample/main.cpp|31|error: ‘int employee::id’ is private /home/jamaj/src/wxTestes/multiindexsample/main.cpp|69|error: within this context| typedef multi_index_container< employee, indexed_by< ordered_unique< tag<id>, BOOST_MULTI_INDEX_MEMBER(employee,int,id)>, ordered_non_unique< tag<name>,BOOST_MULTI_INDEX_MEMBER(employee,std::string,name)>, ordered_non_unique< tag<age>, BOOST_MULTI_INDEX_MEMBER(employee,int,age)> > > employee_set; So, I had to change the scope of index class members to public, and it worked: class employee { public: int id; std::string name; int age; employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){} friend std::ostream& operator<<(std::ostream& os,const employee& e) { os<<e.id<<" "<<e.name<<" "<<e.age<<std::endl; return os; } }; The question is: is there any other way to do it without exposing all class members? Thanks in advance. Best Regards. José Augusto Jr. jamaj

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[multi_index] How to use a class instead of a struct with the boost:multi_index_container?
by jamaj 14 Nov '10

14 Nov '10

Dear All, I want to use a class instead of a struct to create a multi_index container. But the example that comes with the documention (basic.cpp) uses a struct. Which changes (if there are any) must I make in order to use this container with a class of objects, instead of with structs? Thanks in advance. Best Regards, José Augusto Jr. (jamaj)

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Doubt about using boost:multiindex containers with classes
by José Augusto Jr. 14 Nov '10

14 Nov '10

Dear All, I've written a set of classes. Suppose I have a class called WorkCenter and another called Machine. I created a smart pointer to each Machine object. Each Workcenter has one or more Machines. I could create a vector of MachineSmartPointers. But I will need to search for Machines by some different index keys, like by the unique ID (an Int) or by Tag (a String). I could not find any example like that. In the Boost documentation the example is made with a struct. I know that a class, in C++, is very similar to a Struct. But I dont know how to write this code. Could someone give me a light on this? Thanks in advance. -- sds. Written by - Escrito por: José Augusto M. Andrade Jr. - JamaJ

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Re: [Boost-users] Boost.Random multithreading
by Steven Watanabe 14 Nov '10

14 Nov '10

AMDG On 11/14/2010 7:03 AM, Juan Antonio Farré Basurte wrote: > Are random number generators thread safe? Can I use a random number > generator by multiple threads without explicit locking? No. > I guess the answer is no... Then I wonder if every thread could use a > different instance of the same random number generator without interference > between the different generators. > > I guess the answer is yes for pseudorandom generators. But what about > real random generators? If I have different instances of one, they all have > to access the same source of randomness (maybe hardware). Will they > synchronize transparently? random_device reads from /dev/urandom. I assume that this is safe. In Christ, Steven Watanabe

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boost::asio::buffer exception
by Lloyd Kanakkassery 14 Nov '10

14 Nov '10

Hi, I want to write some data using boost::asio::write(). write() has two arguments, one is the stream to which the data to be written and the other is the data buffer. The data buffer can be created using boost::asio::buffer() function. When I use it this way it works. Then, I have tried to wrap boost::asio::bufffer() in my custom function like this boost::asio::const_buffers_1 MyBuffer(string msg) { return boost::asio::const_buffers_1(boost::asio::const_buffer(msg.c_str(),msg.length())); } The I use this in my asio::write() as booost::asio::write(mySocket, MyBuffer("hai")); This program compiles and runs but it throws an exception called "The system detected an invalid pointer address in attempting to use a pointer argument in a call". I understand that, it is associated with the MyBuffer() function. I have checked it with the buffer() function available in "buffer.hpp". Both are written in the same way, but my function is throwing exception. Could you give some hint? Thanks and Regards, Lloyd

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[fusion] named parameter technique with fusion::map
by alfC 13 Nov '10

13 Nov '10

Hi, After I discovered Boost.Fusion I realize that I can define proper named functions with Boost.Fusion. Named in the sense of instrospection (not in the sense of default user parameters). It was something that is easy to achieve but it was very verbose. I simplified a little bit the syntax but at the end I got stuck just before achieving something useful with this ideas. I need a little help towards the end. using namespace boost::fusion; double H(double p, double q){ // original function for reference return p*p + q*q; } struct p{}; struct q{}; double H(map<pair<p, double>, pair<q, double> > const& args){ return H(at_key(args), at_key<q>(args)); } int main(){ cout << H( map<pair<p, double>, pair<q, double> >( make_pair(1.), make_pair<q>(2.) ) ); return 0; } One question: Why I can not interchange the order of p and q in the last call, after all it is a map at the library could in principle differentiate the pairs? making it possible to call an unordered named parameter. e.g. cout << H( map<pair<p, double>, pair<q, double> >( make_pair<q>(2.), // was p make_pair(1.) // was q ) ); Is it possible to interchange the order to give more flexibility to the user? After a little playing I gladly found that the make_pair is not stricly necesary cout << H( map<pair<p, double>, pair<q, double> >(1.,2.) ); which is a nice improvement. It seems that still there is some redundancy, so I tried cout << H(make_map<p, q>(1.,2.)); and worked! On the side of the function definition I can have an alternative syntax which may be shorter but more difficult to interpret: double H(result_of::make_map<p, q, double, double>::type const& args) { ... } although it is not a great improvement. Second question: Does it occur to anyone how simplify things further? This is nice because *in principle* I can distinguish between the two parameters (strictly speaking is all one big parameter) at compile time via templates. Third question: I say in principle because I am stuck here. For example how can I implement a named parameter bind? It seems to me that I am close to achieving this but I don't know exactly how. What I want is some kind of "bind<H, q>(3.0)" which is a function object that effectively evaluates to H( pvalue, 3.0) or to H(make_map(pvariable), 3.0) when calling bind<H, q>(3.0)(pvalue) or bind<H, q>(3.0)(make_map(pvalue)). Note that the most general case is something that defines partial parameters by a map //if H had four parameters: auto b = my::bind<H, set<q1, q2> >( make_map<q1, q2>(3.0, 4.0) ) ; // or my::make_bind<H>( make_map<q1, q2>(3.0, 4.0) ) // and then use it as b(make_map<p1, p2>(5.0,6.0)); I think this seems to be promising although I need a little push to finish the technique I hope it is useful for someone (if I am not reinventing the wheel) and that we can round up the idea. or just wanted to know some opinions. Thank you, Alfredo (Note, named parameter boost library is not the proper way to go here because the of the level of instrospection I need in the functions, and because the use of named parameters is not to omit passing parameters but to recognize 'externally' certain parameters).

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