August 2008 - Boost-users - lists.preview.boost.org

[BGL] citing the Boost Graph Library
by Alejandro Marcos Aragón 06 May '09

06 May '09

Can anyone point me how to cite the Boost Graph Library in a paper? Is there any information in the boost website? Thank you all, Alejandro Aragón

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compile-time check that a member function exists
by John Pretz 25 Mar '09

25 Mar '09

Hi, I'm pretty new to boost. I want to write some code with a compile-time check whether a member function exists or not. The code below shows kinda what I need except I'd obviously like to avoid a specialized template for each class that I use. Can anybody point me in the right direction? Thanks, John **************************************** #include <iostream> using namespace std; struct WithMemberGo { void Go() const {cout<<__PRETTY_FUNCTION__<<" going...."<<endl;} }; struct WithoutGo { }; template <class T> void CallGoIfItExists(const T& t){ t.Go(); } // I want to avoid having to specialize this function for every class without the // right member function. template <> void CallGoIfItExists<WithoutGo>(const WithoutGo&){ cout<<"not going anywhere...."<<endl; } int main(){ WithMemberGo with; CallGoIfItExists(with); WithoutGo without; CallGoIfItExists(without); } -- John Pretz -- P-23, MS H803 Los Alamos National Lab Los Alamos, NM 87545 Phone: (505)665-5847 Fax: (505)665-4121

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Boost.Graph set of edges
by James Sutherland 17 Mar '09

17 Mar '09

Can you do something like typedef boost::graph_traits<Graph>::edge_descriptor Edge; Edge e; .... std::set<Edge> edges; edgeSet.insert( e ); I am getting compiler errors that imply that the edge_descriptor does not implement the < operator. Thanks, James

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serial programs
by Steven Woody 02 Mar '09

02 Mar '09

Hi, I want to write a portable program which need to read/write serial ports. How can boost help this? Thank you. ( I got know basic serial programming in Linux but I have no idea how that it done in Windows ) -- woody then sun rose thinly from the sea and the old man could see the other boats, low on the water and well in toward the shore, spread out across the current.

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Re: [Boost-users] metafunction invocation performance
by Hicham Mouline 26 Feb '09

26 Feb '09

The solution to this one is provided by Joaquin, in his reply below: I tried compiling your code with MSVC++ 8.0 and it is indeed incredibly slow. After playing a little with the code I realized that MPL views are the culprit here: for some reason it is much faster to fold on a vector-based computation rather than a view: template<typename Sequence1,typename Sequence2> struct sequence_product : boost::mpl::fold< Sequence1, boost::mpl::vector0<>, boost::mpl::copy< boost::mpl::transform< Sequence2, pair_with<boost::mpl::_2> >, boost::mpl::back_inserter<boost::mpl::_1> > > {}; This transformation on sequence_product and seq_seqpair_product alone improved the performance tremendously. Additionally I've tried a small optimization: in seq_seqpair_product it is preumable better to fold on Sequence rather than SequencePair, since on average the first is expected to be shorter. Truth be said, I haven't detected any improvement with this, anyway. > Shouldn't there be a dot-product or cross-product of mpl sequences as > a general algorithm? and not just 2 sequences but N. I guess it is the O(n^2) behavior that deterred the author from including the algorithm (much as STL usually does not contain quadratic algorithms). It might be a worthy addition, nonetheless Joaquin --------- Interesting why a joint_view slower than the alternative. This result confirmed then on MSVC8 , gcc4.1, Intel10... regards, /Hicham

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[date_time] posix_time::time_duration::operator<< fails for hours>23
by Soren Dreijer 04 Feb '09

04 Feb '09

I'm creating a posix_time::time_duration object based on the minutes() helper function. If I specify a large value, such as 2000, I get a time_duration of 33:20:00. Take a look at the following piece of code, though: time_duration td = minutes(2000); cout << to_simple_string(td); // OK cout << td; // Fails with an assertion in VS2008 The latter call fails with the following assertion in strftime.c on line 658: _VALIDATE_RETURN( ( ( timeptr->tm_hour >=0 ) && ( timeptr->tm_hour <= 23 ) ), EINVAL, FALSE) Apparently, operator<< expands to _expandtime(), which doesn't allow values for the hour to be greater than 23. Is this intended behavior, or should I just always use to_simple_string() rather than the convenient operator<< ?

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thread_group / removal of items
by Christian Ost 13 Dec '08

13 Dec '08

Hi, I have a question concerning the removal from entries of a thread_group. Consider the following code (i am working on a small threaded server): in TCPServer.h: boost::thread_group threads in TCPServer.cpp: int TCPServer::loop(int listen_fd) { for (;;) { [connect client] boost::thread* thrd = new boost::thread(boost::bind(&TCPServer::readMessages, this, rfd)); threads.add_thread(thrd); } } } int TCPServer::readMessages(int rfd) { boost::this_thread::at_thread_exit(boost::bind(&TCPServer::exitThread, this)); for(;;) { [read message] if ([buffer is empty]) { [close connection] return(0); } } return 1; } void TCPServer::exitThread() { cout << "thread exited" << endl; } Now I would like to remove the exited thread from the thread_group, however to do this I would need its thread* object - but the maximum of information I can get from boost::this_thread is a boost::thread::id and I haven't found a possibility to get a thread by its thread::id so far. How can/should I solve this issue? I would be quite happy about any advice... Thank you very much! Christian

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[graph] property_map from bundled properties in a subgraph, how?
by Christian Rössel 28 Nov '08

28 Nov '08

Hi, thanks for the great graph library! My first attempts with boost.graph were quite successful, but now I'm stuck. My question is: How can I get a property_map from bundled properties in a subgraph? (boost 1.34.1, g++ and VC8) In the beginning I had a bidirectional graph with bundled properties and I used a property map from the edge's bundled properties: #include <boost/graph/adjacency_list.hpp> #include <boost/graph/subgraph.hpp> using namespace boost; struct VertexProperty { // ... }; struct EdgeProperty { double length_; // ... }; typedef adjacency_list<vecS, vecS, bidirectionalS, VertexProperty, EdgeProperty> Graph; int main () { Graph g; typedef property_map<Graph, double EdgeProperty::*>::type EdgeWeightMap; EdgeWeightMap ewm = get (&EdgeProperty::length_, g); // use ewm in an algorithm ... return 0; } Everthing worked fine. Then, I had to change the graph-type from adjacency_list to subgraph ... typedef subgraph< adjacency_list<vecS, vecS, bidirectionalS, property<vertex_index_t, int, VertexProperty>, property<edge_index_t, int, EdgeProperty> > > Subgraph; int main () { Subgraph g; typedef property_map<Subgraph, double EdgeProperty::*>::type EdgeWeightMap; EdgeWeightMap ewm = get (&EdgeProperty::length_, g); // use ewm in an algorithm ... return 0; } ... and got this compile error: In instantiation of `boost::property_map<Subgraph, double EdgeProperty::*>': subgraph_property_map.cpp:45: instantiated from here ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:355: error: no type named `vertex_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:356: error: no type named `edge_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:360: error: no type named `vertex_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:360: error: `value' is not a member of `<declaration error>' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:364: error: no type named `vertex_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:364: error: `value' is not a member of `<declaration error>' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:367: error: no type named `vertex_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:367: error: `value' is not a member of `<declaration error>' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:369: error: no type named `vertex_bundled' in `class Subgraph' ../../vendor/boost_1_34_1-multithread/boost/graph/properties.hpp:369: error: `value' is not a member of `<declaration error>' Is there a way to use property maps from bundled properties in a subgraph? If not, can you give me a hint for a workaround, please. Thanks and best regards, Christian __

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Random: Using random generators with runtime parameters
by Hans Mull 23 Nov '08

23 Nov '08

Hi! How can I use random generators with multiple parameters such as linear_congruential with parameters that are only known at runtime? Thanks in advance, Hans

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[boost-users][bind, signal] binding a weak_ptr?
by Igor R 12 Nov '08

12 Nov '08

Hello, When using shared_ptr, we usually take an advantage of weak_ptr to break the "cycles". But sometimes the "forth connection" between the objects is by means of shared_ptr, while the "back connection" is by means of signal-slot connection. Like this: shared_ptr<Class1> o1; shared_ptr<Class2> o2; o1->someSignal_->connect(bind(&Class2::responder, o2)); // besides, o2 has a shared_ptr to o1 I'd like this signal-slot to be "weak", i.e. instead of "bind(&Class2::responder, o2)" I wish it could be "bind(&Class2::responder, weak_ptr(o2))" - which is illegal. Of course, I can define (and connect to the signal) a wrapping functor that would store a weak_ptr to the wrapped object, and would try to lock it in operator(). But probably boost already have some off-the-shelf solution for this issue? Thanks!

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