May 2011 - Boost-users - lists.preview.boost.org

Need help with compiling boost::function and ublas::matrix
by archie14 05 May '11

05 May '11

I am getting compiler error using boost::function and boost::numeric::ublas as function return value. I am sure I am not declaring something right, but I can't quite catch where (probably the "const" member function specifier). Any help will be greatly appreciated. Code to reproduce the problem is shown below. If #include <vector> #include <boost/function.hpp> #include <boost/numeric/ublas/matrix.hpp> using namespace boost::numeric::ublas; class Foo { public: int bar() const { return 1; } const matrix<double>& stdev() const { return _stdev; } private: matrix<double> _stdev; }; typedef std::vector<Foo> container; class invoker { public: invoker (container* cont, boost::function<int (Foo*) > t) : f(t), _cont(cont) { for (container::iterator it = _cont->begin(); it != _cont->end(); ++it) { Foo& foo = *it; int i = f(&foo); } } // compiler generates error if following code // is uncomennted together with the call in _tmain // invoker (container* cont, // boost::function<const matrix<double>& (Foo* const) > fmatrix) // : _fmatrix(fmatrix), _cont(cont) // { // for (container::iterator it = _cont->begin(); // it != _cont->end(); ++it) // { // Foo& foo = *it; // const matrix<double>& stddev = _fmatrix(&foo); // } // } private: boost::function<int (Foo*) > f; boost::function<const matrix<double>& (Foo* const) > _fmatrix; container* _cont; }; int _tmain(int argc, _TCHAR* argv[]) { container lst (5); std::fill(lst.begin(), lst.begin() + 5, Foo()); invoker invbar(&lst, &Foo::bar); // uncomment this line together with method in "invoker" to generate error // invoker invstdev(lst, &Foo::stdev); return 0; }

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Adjacency List vertex access
by Carlo jardinier 05 May '11

05 May '11

I try to use the adjacency list from boost. I can fill the list with vertices and edges, but somehow I cannot access a specific vertex or edge. For example this is not working (see test.cpp): ** struct EdgeProperties { bool bConnectedBond; EdgeProperties(){bConnectedBond=false;} }; struct VertexProperties{ int index; int spin; bool bOnCluster; VertexProperties(): spin(){ bOnCluster = false;} ~VertexProperties(){ } }; typedef adjacency_list< vecS, vecS, bidirectionalS, VertexProperties, EdgeProperties > Graph; typedef graph_traits< Graph >::vertex_iterator Vit; Graph g(9); unsigned int i = 3; Vit vi; vi = vertex(i,g); ** I want vi to bi an iterator that points on the 3. vertex of the graph g. I attached the error message from g++ when compiling. Can anyone help?

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[Signals] Is connection::disconnect() "const-correct"?
by Greg Hickman 05 May '11

05 May '11

For a connection 'c', if c.connected() == true prior to calling c.disconnect(); after which c.connected() == false, how can connection::disconnect() be considered a "const" member function since it clearly changes the observable state of a connection?

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dereferencing type-punned pointer will break strict-aliasing rules
by Hossein Haeri 05 May '11

05 May '11

Dear all, [Boost 1.46, GCC 4.5.1, MinGW32, WinXP SP3] I use a number of Boost libraries that I see emit the following warning in GCC under release build: "dereferencing type-punned pointer will break strict-aliasing rules" I have traced the code (of SmartPtr and Function specifically) and it's always with an operations like reinterpret_cast<T*>(...)->~T(). Now, I'm wondering how safe this reinterpret_cast is? How serious should I take this warning here? (I do already know how to turn it off or the strict aliasing check.) And, more than anything else: Is this warning suggesting an improvement in my own code? TIA, --Hossein

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Specifying an outgoing interface for IPv6 multicast
by Jay Katti 04 May '11

04 May '11

Folks, Has anyone figured out how to specify the outgoing interface for IPv6 multicast using the boost asio library socket options on Linux ? See snippets below... What value does one specify for "unsigned int ipv6_interface" in the network_interface constructor ? Tried specifying the interface index (1..3 on my host) but that did not work. Thanks, Jay .. >From multicast.hpp * Implements the IPPROTO_IP/IP_MULTICAST_IF socket option. * * @par Examples * Setting the option: * @code * boost::asio::ip::udp::socket socket(io_service); * ... * boost::asio::ip::address_v4 local_interface = * boost::asio::ip::address_v4::from_string("1.2.3.4"); * boost::asio::ip::multicast::outbound_interface option(local_interface); * socket.set_option(option); * @endcode * * @par Concepts: * SettableSocketOption. */ #if defined(GENERATING_DOCUMENTATION) typedef implementation_defined outbound_interface; #else typedef boost::asio::ip::detail::socket_option::network_interface< IPPROTO_IP, IP_MULTICAST_IF, IPPROTO_IPV6, IPV6_MULTICAST_IF> outbound_interface; #endif ========================================================== From: socket_options.hpp ... // Construct with IPv6 interface. explicit network_interface(unsigned int ipv6_interface) { ipv4_value_.s_addr = boost::asio::detail::socket_ops::host_to_network_long( boost::asio::ip::address_v4::any().to_ulong()); ipv6_value_ = ipv6_interface; }

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Re: [Boost-users] [msm] EUML and State construction
by Christophe Henry 04 May '11

04 May '11

> I'm trying to construct some euml states with data at the time of the state > machine construction. The below boils down what I'm trying to do and > fails to compile. Should I expect this mechanism to work with the euml > frontend ? Yes you should but there is a bug, thanks for reporting it. <snip code> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > With gcc 4.5 and Boost 1.46.1, I get: > > simpletest.cpp: In function 'int main()': > simpletest.cpp:30:75: error: no match for 'operator<<' in > 'boost::msm::back::states_ << test_state_with_constructor(1)' Ok, I see what it is, I did not solve correctly my conflict between proto and serialization. I just committed a fix into the trunk (revision 71719), but it's not working, I simply run into my next proto problem :( I'll continue working on this tomorrow. Thanks, Christophe

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[unordered_map] Trying to understand some errors
by Craig Longman 04 May '11

04 May '11

I'm using VS v9, just in case that matters in this case. I'm : using namespace std; using namespace boost; unordered_map< string, uint32_t > xrf1; unordered_map< string, uint32_t >::const_iterator& iter = xrf1.find( "hello" ); This is something I've used many times with the other containers (well, std::map at least), but here I'm getting a conversion error. This is resolved by either removing the reference marker, or removing the const qualifier. Can someone explain this please? I'd always thought that applying const was easily done, and if so, then a reference should be sufficient, right? Unless the const cast is marked as explicit somehow? And as a side(ish) question, is there any real need to worry about have an object versus reference to something like an iterator? I've always tried to use references where I can, but I wonder if I should "just say no" and use regular objects from now on? Thanks, -- Craig Longman If it's not *signed* by me, then please don't assume it *is* from me.

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[BGL] Extending Floyd Warshall (was: All-pairs SP algorithms -> Determine the path)
by Nicholas Mario Wardhana 04 May '11

04 May '11

On 16 April 2011 02:42, Jeremiah Willcock <jewillco(a)osl.iu.edu> wrote: > Hi Jeremiah, My apology for digging up an old post. I'd like to ask how Boost's Floyd Warshall can extended to provide further functionality. I cannot find any notion of visitor for Floyd Warshall, unlike Dijkstra and A*, and I am a bit confused about the types of the arguments that have to be passed to the function. > One thing you can do in BGL is to compute the paths using the distances; > look for edges where the source and target distances from a particular > starting node differ by the edge's weight, and that will be in the SSSP tree > for that starting node. You can also change the distances to <distance, > predecessor> pairs (just by changing the types being passed into the > algorithm); Will that be a variable of type std::vector<std::vector<std::pair<float, boost::vertex_descriptor>>> ? I tried this and the code failed to compile. > you would still compare just the distances, and the weight of an > edge would be a pair <actual_weight, source>. Will that be a std::pair<float, vertex_descriptor> variable? Additionally, is it also possible to know the number of nodes in a shortest path between two vertices in the graph by using Boost's Floyd-Warshall implementation? > > -- Jeremiah Willcock Thank you. Best regards, Nicholas

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[asio] Joining a group on a specific interface not documented
by Dylan Klomparens 04 May '11

04 May '11

I discovered today that the boost::asio::ip::multicast::join_group option has a constructor to specify a local address to use when joining a multicast group. Unfortunately, this constructor is not documented. How can I contribute to the boost documentation or contact the author to request an update in the documentation?

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Force boost::asio::buffer to copy by value.
by Slav 04 May '11

04 May '11

Hello. I use boost::asio::buffer to send a message using void Send(const std::string& messageData) { socket.async_write(boost::asio::buffer(messageData), ...); } And encounter "string iterator not dereferencable" runtime error somewhere within io_service' thread. When I create objects' variable to store message data for the buffer: void Send(const std::string& messageData) { this->tempStorage = messageData; socket.async_write(boost::asio::buffer(this->tempStorage), ...); } the error is never occured. std::string (to which messageData is referenced to) is freed almost right after Send() calling - does boost::asio::buffer stores just a reference to object? If so, how can I force it to store the data by value?

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