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bzip2_compressor help
by Bryan S 14 Oct '10

14 Oct '10

I know that I'm doing something stupid but it isn't obvious to me what. I'm trying to write a compressed file using: namespace BI = boost::iostreams; BI::filtering_ostream out; std::fstream mfile("test.gz", std::ios::binary|std::ios::out); out.push(BI::bzip2_compressor()); out.push(mfile); out << "This is a gz file" << endl; but when I do so, the file is always empty. Commenting out the push of the bzip2_compressor works like I'd expect. Any help for a newbie? Thanks B

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Re: [Boost-users] [Boost.Spirit] Synthesised attributes and sub-rules
by Hartmut Kaiser 14 Oct '10

14 Oct '10

> On 14 October 2010 22:36, Hartmut Kaiser <hartmut.kaiser(a)gmail.com> wrote: > > That should be easy, see below. > > > > start = a_rule | b_rule | c_rule; > > > > qi::rule<Iterator, std::vector<int>()> a_rule; > > qi::rule<Iterator, std::vector<int>()> b_rule; > > qi::rule<Iterator, std::vector<int>()> c_rule; > > > I think I tried something like that, but it didn't work. Unless I'm > mistaken, each of those rules will create their own std::vector<int> > instance, so the values will not end up inserted into the vector specified > in the grammar parameter. No, it should work. The vector attribute is propagated to the alternatives, where it is filled. > I was able to eventually achieve my goal by specifying each of the rules > like so: > > qi::rule<Iterator, std::vector<int> &> a_rule; > > and in the main grammar I passed the _val into them. > > start = a_rule(_val) | b_rule(_val) | c_rule(_val) > > Then I referenced the arguments with _r1 in the sub-rules. > > Does that look correct? Is there a better way? That should work as well. This might be a tick better in terms of performance, even. But I'm guessing here, I have not done any measurements. Regards Hartmut --------------- http://boost-spirit.com

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where is lexical_cast.hpp?
by alapex0310＠gmail.com 14 Oct '10

14 Oct '10

Hi, I want to use boost::lexical_cast but cannot find lexical_cast.hpp in the boost tree. I am using VS2008. Has it been moved somewhere? I am trying to use boost 1.44. Thanks a lot in advance, -Al

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[fusion] memory layout of fusion::vector vs boost::tuple/boost::array
by alfC 14 Oct '10

14 Oct '10

Hi, I am trying to convert a boost::array into a fusion::vector. reinterpreting the memory from boost::array. It works for tuples but not fusion::vector, why is that. Is there a way to make it work? ( I was hoping that the memory layout is the same to make conversion from one to the other very easy.) #include <boost/fusion/container.hpp> #include <boost/fusion/include/container.hpp> #include<boost/array.hpp> #include<iostream> #include<boost/tuple/tuple.hpp> using std::clog; using std::endl; int main(){ boost::array<double, 3> ba={{1.0, 2.1, 3.2}}; clog << "ba: " << ba[0] << ", " << ba[1] << ", " << ba[2] << endl; using namespace boost::fusion; vector<double, double, double> bfv( reinterpret_cast<vector<double, double, double>&>(ba) ); //doesn't work as expected clog << "bfv: " << at_c<0>(bfv) << ", "<< at_c<1>(bfv) << ", " << at_c<2>(bfv) << endl; using boost::tuple; tuple<double, double, double> btt(reinterpret_cast<tuple<double, double, double>&>(ba) ); // works! clog << "btt: " << btt.get<0>() << ", "<< (btt).get<1>() << ", " << (btt).get<2>() << endl; return 0; } outputs: ba: 1, 2.1, 3.2 //original data bfv: -9.25597e+61, -2.35344e-185, 4.87507e-270 //not expected btt: 1, 2.1, 3.2 //works! Let me give some context, the reason I am doing this is that I need to interface fusion::vector of boost::quantities (all have the sizeof double) and adimensionalize the list of quantities into an array of doubles and vise-versa In reality, the final goal is to get this to work: boost::array<double, 3> ba={{1.0, 2.1, 3.2}}; vector<quantity<si::length>, quantity<si::time> , quantity<si::mass> > bfv( reinterpret_cast<vector<quantity<si::length>, quantity<si::time> , quantity<si::mass> >&>(ba) ); (or other generic option to go from array<double, N> to vector<quantity<T1>, quantity<T2>, ... quantity<TN> >) but since I can't make it work with simple 'doubles' I am asking why this could be done. Thank you again, Alfredo

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Re: [Boost-users] [serialization] Deserialize by pointer withoutcalling new/constructor
by averigin 14 Oct '10

14 Oct '10

> It's not the most common scenario. It can be addressed, but requires > some more complete understanding of the library. The library "just works" > for the common cases. > > Think about why you have a base class pointer in your class which will > "never change". That is, if you recover it with out re-creating it, > you're > assuming that in the meantime the following statement has not been > executed. > > my_base_ptr = some_derived_ptr; > > That is, you're writing code on an assumption which you can't enforce. > If someday, in some other code module, far, far, away .. someone > executes the above, you'll have some unrecoverable mess to deal with > with no clear idea of what the source of the problem is. > > Sooo - my suggestion is to replace > > struct my_thing { > Base *m_ptr > ... > }; > > with > > struct my_thing > Base &m_b > ... > }; > > This will "just work" as far as serialization is concerned. > > Now if making the above change in your program is hard to do, you should > think about it a little bit more before you insert a booby trap into your > program. > Usually, this will entail some refactoring to get things back together > again. > But the result will be something more robust, less likely to contain bugs, > easier to test and aintain. Here's an attempt to further explain and (hopefully) clarify what's happening and why. 4 pieces of background to start, then I'll try to tie it all together. 1. In OMNeT, there are two main components to a simulation: Simple Modules, which have associated functionality (i.e., code), and Compound Modules, which are containers for simple modules and have no associated code. Note, for reference, the module types are termed cSimpleModule and cCompoundModule, both derived from cModule. All simple modules are derived from cSimpleModule and all compound modules are derived from cCompoundModule. 2. In a simulation it's possible to lookup another module (M_i) from the active module (M_a) and invoke methods on M_i. The lookup functions return a cModule pointer to M_i, which then must be dynamically cast to M_i's most-derived type to invoke its methods. However, that cast requires including M_i's header file in the code for M_a, which can result in ugly dependency trees. Thus, serializing by a looked-up cModule (base-class) pointer keeps things 'nice'. 3. When dynamically generating modules, they are created using a module factory which configures some internal state information which is not publicly accessible. Also, note that the factory method returns a cModule pointer. 4. When I run simulations, serialization and deserialization never occur during the same simulation; either the simulation starts fully configured and eventually serializes its state immediately before terminating, or it starts with a minimal skeleton and constructs the rest of the modules based upon a previously stored state. Now to put all the pieces together. When saving a simulation state, it's necessary to serialize a number of compound modules. So far, I've done this by adding a simple "archiver" module to them. I lookup the "archiver" module using the lookup functions and try to serialize the resulting cModule pointer. This causes the "archiver" module to save what information is publicly accessible (i.e., there is some internal state information it cannot access). When loading a saved state, the minimal skeleton includes one of the above mentioned "archiver" modules. It creates the input archive and then tries to create the other modules in the simulation. This is where I run into problems. What I wanted to do was have the "archiver" module create the other modules using their associated factories and then deserialize the rest of their state via the cModule pointers returned by the factories. This way the factory configures the module's private internal state information and the everything else is loaded from the archive, and this minimizes file dependencies (i.e., including header files for derived types). (I realize this isn't true (de)serialization, so I refer to it as partial-serialization.) However, this conflicts with the normal method for pointer deserialization, which would allocate memory for a new module, initialize it and then deserialize the information from the archive into that new object, which (in my case) is then promptly deleted or leaked. The only alternative I can see would be to dynamically cast the cModule pointers and directly call their serialize() or save()/load() methods directly. However, this seems like an ugly hack since that requires making the serialization methods public and including derived-class headers all over the place. Thus, I would like to stick with my partial-serialization method. I'm just not sure if it's possible to "easily" implement what I need for the loading portion. > > Of course if you're working in an environment whose controlling principle > is "just make it work right now", you're out of luck. You'll just have to > bury the bomb in your program and hope you're not in the immediate > vicinity when it blows up. > While I don't quite see it as a bomb, I know that probably just indicates short-sightedness on my part. Regardless, I am in the "just make it work right now" boat, so any help you can offer would be much appreciated. Regards, Adam Verigin P.S.: I did manage a temporary hack of archive/detail/iserializer.hpp pointer_iserializer::load_object_ptr() that (badly) assumed that if the passed pointer is not NULL, then it is a pointer to an allocated object so there's no need to create a new object. Coupled with a do-nothing load_construct_data() method this worked great for partial-deserialization, but causes memory corruption for normal deserialization since the assumption is not always true (nor is it a good assumption to try an force on other users).

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[Smart Ptr] Why is weak_ptr a _ptr?
by Szymon Gatner 13 Oct '10

13 Oct '10

Hi, Is it just me or is it really the worse naming in whole boost library? It is nothing like any other smart pointer. No initialization / construction from raw pointer. No operator * or -> (the very least one would expect from _ptr class). No get(). And many more which I now forgot. My point is that is is not a pointer at all, not even a bit. It only happens to have a member variable returning one and that is hardly a reason to call type pointer-like. It should rather be called shared_tracker or shared_listener or something in that taste ;) Regards, Szymon

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Proto domains shenanigans
by joel falcou 13 Oct '10

13 Oct '10

OK, I have a situation in which proto domain/subdomain could help me but i can't wrap my head around a proper solution. Here is the deal, i have various sub EDSL that goes like: - constants EDSL provides named consatnts (like zero_, one_, pi_ etc) that are meant to be terminal usable in any other EDSL en provide a type based way to know which constant is beging used and provide optimization in came it helps (e.g detecting x < zero_ in SIMD EDSL to replace with the SSSE3 corresponding fused operation) - a SIMD vector EDSL - various container based EDSL : table (multidim array), vector, matrix and tensor, polynom and rigid_transform. The rules I want to have is : - constant can mix with any other EDSL - SIMD don't mix with anybody - table mix with every other container and make them evaluates as table (e.g matrix * table == elementwise product and not matrix product) - vector, matrix, tensor can mix - polynom can mix with table but not with vector, matrix, tensor - rigid_transform van mix with table and matrix However i can't find any combination of domain definition that satisfy all. Is there some systematic methodologies to not fail at that ?

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[asio] DNS query
by for-gmane 13 Oct '10

13 Oct '10

Hi, is it possible to do DNS queries with asio? (for example getting the MX record(s) of a domain)

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[units] quantities with system abstraction "any<length>"
by alfC 13 Oct '10

13 Oct '10

Hi, In order to avoid reinventing the wheel I was wondering if there is any effort or there was any attempt to further abstract boost::units::quantities from its unit system but with a given dimension. That is, an object that can hold any boost::units::quantity<unit<Dimension, System> > with a given Dimension fir any System. For example (names are not ideal) any<length_dimension> a1 = 2.*si::meter; // RHS is type quantity<si::length> any<length_dimension> a2 = 2.*cgs::centimeter; //RHS is type quantity<cgs::length> any<length_dimension> b1 = 2.3 * si::second; // ERROR. or can hold any other quantity with length dimension (from any system). A sort of boost::variant<quantity<Dimension, system1> , quantity<Dimension, system2>, ... >, (but since the list is of type is not well defined maybe variant is not an options.) I know that there are some unresolved issues, for example, what is the result of a1 + a2, for which I have some solutions in mind. Anyway I just was wondering if this was tried before. And if not, what would be the best way to achieve it (boost::any? boost::variant?). (Note that all quantity<Unit> types has always the sizeof a double.) Alfredo

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Boost serialization through base class
by Joe Drumm 13 Oct '10

13 Oct '10

Hi, I've tried using the most basic example I can find in the documentation to serialize a class using a pointer to a polymorphic base. However, it only serializes the base class. I'm currently on 1.34.1. Am I missing something obvious? Sample code below: class base { public: friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int) { } }; class derived : public base { public: derived() : foo(5) { } friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int) { boost::serialization::base_object<base>(*this); ar & BOOST_SERIALIZATION_NVP(foo); } int foo; }; BOOST_CLASS_EXPORT_GUID(base, "base") BOOST_CLASS_EXPORT_GUID(derived, "derived") TEST(OMSTestSuite, BasicDeserializeTest) { std::ofstream ofs("test.out"); boost::archive::xml_oarchive toa(ofs); base *b = new derived; toa & BOOST_SERIALIZATION_NVP(b); }

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