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

iostream gzip / bzip header
by Kraus Philipp 09 Dec '10

09 Dec '10

Hello, I'm using bzip and gzip iostreams algorithms, but is there a solution to remove the header data of the compressed stream? I need only the compressed data not the header. Thanks Phil

2 1

Re: [Boost-users] variant over base and derived classes
by Hicham Mouline 09 Dec '10

09 Dec '10

-----Original Message----- From: "Hicham Mouline" [hicham(a)mouline.org] Date: 09/12/2010 03:22 PM To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] variant over base and derived classes >>-----Original Message----- >>From: "Diederick C. Niehorster" [dcnieho_at_[hidden]] >>Date: 09/12/2010 01:51 PM >>To: boost-users_at_[hidden] >>Subject: Re: [Boost-users] variant over base and derived classes >>(sorry if this is a top post, my phone shows no msg quotes) >>I'm no expert on this, but isn't there an compile time function to >>testing if an instance is derived from another (in introspection or >>something)? You could then maybe sort the variant types for most to >>least derived and then test untill you find the suitable cast? >>Just brainstorming pretty much. Hope its useful! >>Best, >>Dee >yes, there is boost::is_base_of or some metafct like that in type_traits. >not quite sure how to implement the sort though? >will checkout mpl::sort with binary predicate base_or_derived. >I have under 10 types, so compile time should be ok >thanks, This works. The source is pasted below. I am however obliged to 1. declare a default-constructed variant 2. call mpl::for_each on the sequence of types in the variant a assign functor to assign to the variant. Is there a way I can embed/simplify this 2 stage construction? regards, Here is the source :-) #include <iostream> #include <boost/variant.hpp> #include <boost/type_traits/is_base_and_derived.hpp> #include <boost/mpl/sort.hpp> #include <boost/mpl/vector.hpp> #include <boost/mpl/lambda.hpp> #include <boost/mpl/for_each.hpp> #include <boost/mpl/not.hpp> #include <boost/mpl/logical.hpp> struct S { virtual ~S() {} }; struct Deriv1 : public S { virtual ~Deriv1() {} }; struct Deriv2 : public S { virtual ~Deriv2() {} }; struct Deriv3 : public Deriv2 { virtual ~Deriv3() {} }; typedef boost::variant<S,Deriv1, Deriv2, Deriv3> my_variant_t; typedef boost::mpl::sort<my_variant_t::types, boost::mpl::not_<boost::is_base_and_derived<boost::mpl::_,boost::mpl::_> > >::type v0_sorted_t; template <typename Variant, typename Base> struct assign { assign(Variant& v, const Base& b) : v_(v), assigned_(false), b_(b) {} template <typename T> void operator()(const T&) { std::cout<< typeid(T).name() <<std::endl; if (!assigned_) { const T* t = dynamic_cast<const T*>(&b_); if (t!=0) { v_ = (*t); assigned_ = true; } } } private: Variant& v_; bool assigned_; const Base& b_; }; int main() { S s; Deriv1 d1; Deriv2 d2; Deriv3 d3; const S& base = s; my_variant_t vvv; boost::mpl::for_each<v0_sorted_t>( assign<my_variant_t,S>(vvv, base) ); std::cout<< vvv.which() <<std::endl; return 0; }

2 1

Re: [Boost-users] variant over base and derived classes
by Hicham Mouline 09 Dec '10

09 Dec '10

>>-----Original Message----- >>From: "Diederick C. Niehorster" [dcnieho_at_[hidden]] >>Date: 09/12/2010 01:51 PM >>To: boost-users_at_[hidden] >>Subject: Re: [Boost-users] variant over base and derived classes >>(sorry if this is a top post, my phone shows no msg quotes) >>I'm no expert on this, but isn't there an compile time function to >>testing if an instance is derived from another (in introspection or >>something)? You could then maybe sort the variant types for most to >>least derived and then test untill you find the suitable cast? >>Just brainstorming pretty much. Hope its useful! >>Best, >>Dee >yes, there is boost::is_base_of or some metafct like that in type_traits. >not quite sure how to implement the sort though? >will checkout mpl::sort with binary predicate base_or_derived. >I have under 10 types, so compile time should be ok >thanks, This works. The source is pasted below. I am however obliged to 1. declare a default-constructed variant 2. call mpl::for_each on the sequence of types in the variant a assign functor to assign to the variant. Is there a way I can embed/simplify this 2 stage construction? regards,

1 0

Re: [Boost-users] mpi/serialization: broadcast function and the value argument
by Hicham Mouline 09 Dec '10

09 Dec '10

-----Original Message----- From: "Matthias Troyer" [troyer(a)phys.ethz.ch] Date: 09/12/2010 02:39 PM To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] mpi/serialization: broadcast function and the value argument >On Dec 8, 2010, at 5:50 PM, Hicham Mouline wrote: >> Following a suggestion from another thread, I have tried broadcasting in a polymorphic way. >> >> I have a hierarchy of polymorphic struct (they have 2 virtual functions). I was wondering if it was possible/allowed to >> >> root process: >> base* b; /// b points to an actual derived struct but may also point the base struct (not abstract) >> broadcast( ..., b, ...); >> >> slave processes: >> base* b; >> broadcast( ..., b, ...); /// broadcast constructs the appropriate struct and makes b point to where it did that >> >> assuming all the conditions for pointer to class conditions are satisfied for the serialization library. >> >If serialization works on your polymorphic class then this should work as well. >Matthias It appears the implementation of mpi::broadcast(), according to this post, http://lists.boost.org/boost-users/2010/12/64802.php and I confirm that expects an already built object to call the (de)serialization procedure on. Therefore, this seems a specific issue that mpi::broadcast() may want to handle differently, could you confirm/correct? thanks,

1 0

serialization: const char*
by Hicham Mouline 09 Dec '10

09 Dec '10

hello, serializing a const char* is not allowed I gather? char* seems not to be allowed either. primitive types pointers are not serializable? I have a struct S{ double d; char c[SIZE]; const char* x; }; template <typename Archive> void serialize(Archive& ar, S& s, const unsigned int version) { ar & s.d; ar & s.c; ar & s.x; } the 3rd one seems to cause the compile error, removing constness didn't help. is one supposed to an array of char or a std::string instead regards,

3 2

mpi/serialization: broadcast function and the value argument
by Hicham Mouline 09 Dec '10

09 Dec '10

Following a suggestion from another thread, I have tried broadcasting in a polymorphic way. I have a hierarchy of polymorphic struct (they have 2 virtual functions). I was wondering if it was possible/allowed to root process: base* b; /// b points to an actual derived struct but may also point the base struct (not abstract) broadcast( ..., b, ...); slave processes: base* b; broadcast( ..., b, ...); /// broadcast constructs the appropriate struct and makes b point to where it did that assuming all the conditions for pointer to class conditions are satisfied for the serialization library. Otherwise, perhaps a solution with a boost::variant over the base struct and all of its derived is the way to go? Thanks,

2 1

Re: [Boost-users] variant over base and derived classes
by Hicham Mouline 09 Dec '10

09 Dec '10

>> -----Original Message----- >> From: Hicham Mouline [mailto:hicham@mouline.org] >> Sent: 09 December 2010 00:04 >> To: 'boost-users(a)lists.boost.org' >> Subject: variant over base and derived classes >> >> hello, >> <snip> >> >> typedef boost::variant<S,Deriv1, Deriv2, Deriv3> my_variant_t; >> >> Deriv3 d3; >> >> struct print_type: public boost::static_visitor<> { >> template <typename T> >> void operator()(const T&) const >> { >> std::cout<< typeid(T).name() <<std::endl; >> } >> }; >> >> const S& s = d3; >> my_variant_t v = s; >> boost::apply_visitor( print_type(), v ); >> >> This prints S. >> >> Is it a truncated copy of d3 that is stored v? >Yes. >> How do I construct v polymorphically so that the real object is stored? >> >> regards, >You have to downcast before creating the variant. >boost::variant only uses the static type of the object. >In Christ, >Steven Watanabe If I am given a const S* sptr, how do I construct an instance of the above variant then? const Deriv1* d1ptr; const Deriv2* d2ptr; const Deriv3* d3ptr; my_variant_t v = ((d1ptr = dynamic_cast<const Deriv1*>(sptr)) != 0 )? *d1ptr: ((d2ptr = dynamic_cast<const Deriv2*>(sptr)) != 0 )? *d2ptr: ((d3ptr = dynamic_cast<const Deriv3*>(sptr)) != 0 )? *d3ptr: *sptr; Is there a better way of writing this? rds, -------------------------------------------- Trying to do this more generically, I've thought of call mpl::for_each on the ::types of the variant to see which dynamic_cast works. The problem is that I need the most derived type to be stored in the variant. I can see how to do it by a virtual function but that is completely intrusive. regards,

2 1

Re: [Boost-users] [Proto] Failed to Mimic the "Lazy Vector" Example
by Hossein Haeri 09 Dec '10

09 Dec '10

Hi Thomas, > > Trying to mimic what comes in the Lazy Vector example > > http://www.boost.org/doc/libs/1_45_0/doc/html/proto/users_guide.html#boost_… <snip> > The type EmtDomain is incomplete when it is used in EmtExpr > (proto::extends ...). So is also lazy_vector_domain when it is used in lazy_vector_expr. What's different here? (See below.) > The solution is to forward declare EmtExpr, define the Domain and then > define the expression wrapper. Thanks, that works. :) But, I do still wonder why the same order of definition for Lazy Vector didn't work here: Grammar > Forward Declaration of Domain > (Context) > Expression Wrapper > Domain Do you mind shedding light on this too? TIA, --Hossein

1 0

Re: [Boost-users] mpi: sending/receiving different types
by Hicham Mouline 09 Dec '10

09 Dec '10

>The way we do this is send a special message saying that a broadcast >will be sent next. > Brian > >probe() checks only for messages sent by send(), not by broadcast(). >Matthias Thanks, I spend most of my time broadcasting, and sometimes sending.... I guess that means in the slave processes: . use mpi::broadcast() . if the received value is a signal that a send() to me will be issued next, then I'll recv() About the broadcast() function, I obviously have many types of messages to send, would you rather: 1. send a broadcast with just an int (like a tag) to tell which broadcast is following next or 2. construct a virtual base class my_mpi_broadcast , derive all the sendable broadcasts from it, from sender, send actual instance of derived from my_mpi_broadcast, and at receiver, can the mechanism reconstruct for me the derived class? (with boost::serialization) Is 2 doable at all? If so, pros/cons regards,

2 4

variant over base and derived classes
by Hicham Mouline 09 Dec '10

09 Dec '10

hello, How to determine the actual type of the object stored in a variant? struct S { virtual ~S() {} }; struct Deriv1 : public S { virtual ~Deriv1() {} }; struct Deriv2 : public S { virtual ~Deriv2() {} }; struct Deriv3 : public Deriv2 { virtual ~Deriv3() {} }; typedef boost::variant<S,Deriv1, Deriv2, Deriv3> my_variant_t; Deriv3 d3; struct print_type: public boost::static_visitor<> { template <typename T> void operator()(const T&) const { std::cout<< typeid(T).name() <<std::endl; } }; const S& s = d3; my_variant_t v = s; boost::apply_visitor( print_type(), v ); This prints S. Is it a truncated copy of d3 that is stored v? How do I construct v polymorphically so that the real object is stored? regards,

3 2