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[graph] template beginner question: How to create a template parameter option
by Christoph 07 Oct '11

07 Oct '11

Hi, i would like to create a generic function, that returns a random bipartite graph like this: enum graph_type {bipartite, none_bipartite}; template <typename Graph> Graph generate_random_graph (unsigned int num_vertices, graph_type t, double density) { if (density > 1) { std::cout << "value of parameter density in Function generate_random_graph is out of range (0.0 - 1): " << density << std::endl; exit(-1); } if (t == bipartite) { Graph g(2*num_vertices); for (int i = 0; i < num_vertices; ++i) for (int j = 0; j < num_vertices; ++j) if (std::rand()%100 <= 100*density) add_edge (i, j+num_vertices, g); return g; } else return Graph(99); // dummy part } @ Then i realized that the option parameter 'graph_type' in 'generate_random_graph' should be a template parameter, too. Like the way we use a template parameter 'boost::undirectedS' in typedef boost::adjacency_list < boost::listS, boost::vecS, boost::undirectedS> my_graph; I don't know where to start from here. I tried to find out the way the 'boost::undirectedS' thing works but i was lost in code jungle. Any assistance is welcome. Maybe you know a nice reference for me to start. If you have any other criticism, please do not hide, i am eager to learn. bye Christoph

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[BGL] boost/graph/graph_utility.hpp - cannot find any documentation
by Christoph 07 Oct '11

07 Oct '11

Hi, i would like to know why it is, that there is no documentation about boost/graph/graph_utility.hpp Functions like 'print_graph' or 'print_edges' are used quite often in the examples, for instance here http://www.boost.org/doc/libs/1_47_0/libs/graph/doc/filtered_graph.html For a newbie, as i am, it is always confusing to have to deal with undocumented functions. How should i start in such a case. I finally did something like find ./ | xargs grep print_edges inside of my boost directory. Are there any other undocumented functions within the Boost Graph Library? best Regards Christoph

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[result_of] Simple question
by Robert Jones 07 Oct '11

07 Oct '11

Morning All It's first thing in the morning for me, so maybe my neurons aren't warmed up, but I was surprised this doesn't work. #include <boost/utility/result_of.hpp> #include <boost/function.hpp> typedef boost::function<int(char)> my_function_type; typedef boost::result_of<my_function_type>::type my_return_type; Doesn't Boost.Function support 'result_of', or am I missing something obvious? If not, is there some other idiom for this, bearing mind that 'my_function_type' might be a Boost.Function, or a true function, or a Boost.Bind? Thx, - Rob.

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Boost IPC shared queue
by sidharth shanbhag 07 Oct '11

07 Oct '11

Hi, I am trying to build a shared queue between a reader and writer thread of my process. I am creating a managed shared memory segment, defining an allocator on top and using the same to initialize a shared queue. I have a question related to the edge case, considering there is a disparity in the speed of the reader and writer threads and the writer thread pumps in more data than the shared segment size, what is the expected behavior of the queue? Will it allocate a new memory segment or block the writer thread or throw an exception? Are there any links or references for the same? I had a look at the boost ipc documentation, but did not see any text explaining this scenario. Thanks and regards, Sid

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Boost Interprocess Question
by Brian 07 Oct '11

07 Oct '11

Hello For simplicity, say I have this: class Animal { int id; }; class Dog : public Animal { int tag; }; class Cat : public Animal { int lives; }; offset_ptr<Dog> a = segment.construct<Dog>(anonymous_instance)(); offset_ptr<Animal> b; b = a; Also assume I have a correctly setup managed_shared_memory called segment. Is there anyway I can delete the constructed object using b? I tried segment.destroy_ptr(b.get()) and segment.deallocate(b.get()) but I get assertion failures. Obviously segment.destroy_ptr(a.get()) would work but I'd like to be able to do it with a pointer to the parent class. Also casting won't work because I won't know if it's a dog or a cat when I delete it. Thanks for any suggestions!

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boost::exception crash when throw from library
by Alexey Badyaev 07 Oct '11

07 Oct '11

Hi all. My little test project (minimal testcase attached to this mail) crashed on ms windows7 when compiled by ms visual studio 2008 express edition. May be, my c++ code is wrong - any help appropriated. -- With best regards, Alexey Badyaev Russian Federation, Kemerovo

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[property_tree] Writing comments in JSON format
by Ruediger Berlich 07 Oct '11

07 Oct '11

Hi there, by trying it out with a modified debug_settings example, I can see that property_tree accepts Javascript ("//") comments inside of the JSON files it parses. I want to find out whether it makes sense to use JSON as an alternative to boost.program_options for configuration files. The idea would be to use a JavaScript-based GUI to modify or create the configuration files in a comfortable way and to use the same files as input for my C++-based programs. As my configuration files are auto-generated by my objects and not everybody loves GUIs, I need to be able to add comments to a property_tree object, so that they are emitted during a "write_json" call. The easiest way to add comments to the config files would be to just add a "comment" data member. This would indeed be very useful for the JavaScript usecase, as comments can be integrated into the GUI / Browser, and would still give guidance to those wanting to modify the JSON files with a standard editor. However, this does not help me to write things like a header, or to add information targeted only at those who modify the files by hand. For these I still need to be able to generate "//"-style comments. From the documentation I could not find out whether this can be done in a standard and portable way. Any pointer would be very welcome! Thanks and Best Regard, Ruediger

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[filesystem] path iterator appends / instead of \ on windows
by Sachin Garg 07 Oct '11

07 Oct '11

In boost v1.47, filesystem\v3\src\path.cpp, inside function m_path_iterator_increment, on line 654, It should be: it.m_element.m_pathname = preferred_separator; Instead of it.m_element.m_pathname = separator; Reason: In below sample code boost::filesystem::path new_path; for (fs::path::iterator i=path.begin();i!=path.end();i++) new_path/=(*i); On windows when iterating a path using above code, line 654 incorrectly appends / instead of \ after drive letter. For example, D:\path\file Becomes, D:/path\file I have created a trac ticket for the same: https://svn.boost.org/trac/boost/ticket/5989 SG

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[boost-users] [serialization] working example of (intrusive) serialization of class with no default constructor? and handling of nested classes with no default constructor
by alfC 07 Oct '11

07 Oct '11

Hi, this question has been asked thousand of times and I still can not see a detailed answer. How can I deserialize a class with no default constructor. The usual response is to point to this documentation http://www.boost.org/doc/libs/1_35_0/libs/serialization/doc/serialization.h… . I read the documentation many time and I can not figure out what does it mean and how it can be used. Does any body has a working small example where this is effectively used? Ideally, I am looking for something like the following, I am willing to accept other options, like making a2 a pointer, etc. int main(){ { A a( ... ); // proper construction syntax std::ofstream ofs("A.xml"); boost::archive::xml_oarchive oa(ofs); a & BOOST_SERIALIZATION_NVP(a); } { std::ifstream ifs("A.xml"); boost::archive::xml_iarchive ia(ifs); A a2(ia); // construct from iarchive or some other intermediate class { a2 & BOOST_SERIALIZATION_NVP(a2); //data can still be loaded in existing object (as usual) } } return 0; } Even if I want to implement my own reading of the xml_iarchive inside the constructor of A, it looks like I need to access the nested elements of the class before accessing to the level of the class (I am thinking in xml terms here). This is where I am stuck, the syntax above forces me to define A::A(boost::archive::xml_iarchive& ia){ ... } If all members are default constructible I can do: A::A(boost::archive::xml_iarchive& ia){ ia & BOOST_SERIALIZATION_NVP(*this); } (yes, the solution in intrusive but the at least I avoid default constructor at all cost) but if one of the member is not default constructible (and I can modify that class) I should be able to do something like, A::A(boost::archive::xml_iarchive& ia) : member1( ...ia?... ){ // ia & BOOST_SERIALIZATION_NVP(member2); // not possible because the archive is still waiting for class of type A to be read } which has two problems, 1) I need to access the elements of the archive (e.g. member2 before A is really handled by boost.serialization) 2.a) for member1 it regresses the problem to the member1 type, which is fine because all this objects will at some point be composed only from build-in "default constructible" types 2.b) if I have no way to modify member1 and it is not default constructible then I can't continue but that is also fine because that means that member1 was not serializable anyway. The real problem is 1). because if I have access to all the classes I will reach a point in which I have to read a built-in class from the iarchive, but I have have access to those nested elements directly, at least not with the documented interface. Thanks, Alfredo

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Creating list of Graphs
by Yajima 06 Oct '11

06 Oct '11

Hi List I would like a help on figuring out how to manage bunch of Graph object as a vector. (vector could be ublas vector or stl doesn't matter) What I'm looking for is an operation that looks like the following: // (It doesn't work as it is.) typedef boost::adjacency_matrix<boost::directedS> Graph; Graph g0, g1, g2; ublas::vector<Graph> ListOfGraphs; ListOfGraphs.resize(3); ListOfGraphs(0) = g0; ListOfGraphs(1) = g1; ListOfGraphs(2) = g2; I'd appreciate it if you could give me an advice. Thank you. -- Yaji

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