October 2008 - Boost-users - lists.boost.org

Design for boost::serialization of STL iterators.
by Carlo Wood 23 May '09

23 May '09

On Sat, Mar 11, 2006 at 11:45:36PM +0200, Peter Dimov wrote: > Carlo Wood wrote: > > > 1) WHY does boost::serialization not support serialization > > of iterators? > > It's very hard, if not impossible, in general. It is either impossible or possible. When it is possible, it can't be hard :p I think that at the moment of serialization, the actual container needs to be known. So, only concentrating on the syntax of the code that serializes an iterator, the following cannot work: ar & iter; However, the container will be known at that point (or at least, we might as well assume that). Therefore, I could imagine a syntax like: ar & foobar(container, iter); where 'foobar' is some template function (that will be part of boost::serialization in the future). Lets start with the last one (have to start somewhere). In order to deserialize the iterator (and taken into account that we already have the container) -- which makes me think that it might be better to pass a functor to operator& above. In other words, (at least for writing), use: template<class Container> struct Foobar { Foobar(Container const&, typename Container::const_iterator& iter) : M_container(container), M_iter(iter); private: Container const& M_container; Container::const_iterator& M_iter; }; and then assign to M_iter, whatever we find in M_container. > If you have access to the container to which the iterator i refers: > > a) if the container is a map, you can serialize i->first, then on > deserialization look up the key in the map using .find(); > > b) if the container is a sequence, and it has the same contents on > deserialization as it does on serialization, you can serialize the index of > the element - distance( c.begin(), i ). I don't think that it is a requirement that the whole container has to be read: either it's a map or set, in which case later insertions will not invalidate the container, or it is a vector, in which case we use an index, from which we can construct the end iterators before the whole container is reconstructed. Therefore, the following syntax can work imho: ar & FooBar(container, iter); Would you agree? There are a zillion questions and implementation details open - but I'd like to get anyones feedback about this type of interface for iterators before continuing. Current questions: What is a good name for Foobar? Am I right when I think that Foobar needs to be declared in boost::serialization? Now the hard part (for me) is that part that involves the internals of the boost library. At the moment one tries to serialize an iterator, it is possible (though not necessarily) that the object that the iterator points to is already serialized. In the case that we are dealing with an associative container (map or set etc), we don't want to store the contents of the object (or key part, in the case of a map) again: I'd like to just store that once, and store a reference in the archive at the other place. How can I make the library store an object only the first time and the store a reference the second time? This would be for an object of arbitrary type thus. I think that it is only feasible to do this when it's actually the same object (same memory address), which is the case; but while storing the object element of the container, the address of it isn't stored as well, is it? Is there a way to make: std::set<SomeData> s; [...] ar << s; Store the address of s (&s) along with the contents of s? And would that then automatically cause the library to not store that same object again when I do: std::set<SomeData>::iterator iter = s.find(...); [...] ar << *iter; Because then, &*iter would again be the same memory address as what was stored before. -- Carlo Wood <carlo(a)alinoe.com>

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[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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Updating my local boost.
by Robert Jones 06 Jan '09

06 Jan '09

I guess this question is more appropriate to the Subversion maillist, but I'm not subscribed to that, so it might take upto 24 hours to appear there. I'm hoping someone here will know the answer! My organisation maintains its boost libraries under its own Subversion repository. This strikes me as a bit odd, but no reason really why not AFAICS. However, the version in our repository is 1.33.1, and I'd like to upgrade to latest 1.36 release. Our network prevents me accessing the Boost subversion repository, so I have to download the tarball and unpack. Then what do I do? I basically want to overwrite our existing boost code with the newer code, but maintain our local edit history so we can see what's changed locally between our old boost code and new. Hence there are lots of additions, changes and deletions, all of which I want to be able see (that's see the differences between our old code and new code, not all the individual boost commits). How can I do this? Thanks - Rob.

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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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