November 2005 - Boost-users

[serialization] trouble with member_saver / member_save ?
by William Kemper 21 Nov '05

21 Nov '05

In 1.33.0 split_member uses: template<class Archive, class T> struct member_saver { static void invoke( Archive & ar, const T & t, const unsigned int file_version ){ access::member_save(ar, t, file_version); } }; And member_save looks like: template<class Archive, class T> static void member_save( Archive & ar, //const T & t, T & t, const unsigned int file_version ){ t.save(ar, file_version); } So the compiler complains about converting a const T to a non const T. It's curious that the source has the const T& in member_save commented out. Is there a workaround for this? Or is it planned to be fixed in the next release?

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Re: [Boost-users] lambda and shared_ptr?
by Mark Santaniello (AMD) 21 Nov '05

21 Nov '05

> > template< typename T > > > boost::function<T(T)> foo( T n_ ) > > { > > //Works, but leaks n > > //T *n = new T( n_ ); > > > > //Doesn't work > > boost::shared_ptr<T> n( new T(n_) ); > > > > return ( *n += _1 ); > > I think that you need to wrap n in boost::lambda::constant: > > return *constant(n) += _1; > > Without it, *n is evaluated immediately. > > > } > Peter, Thanks for the reply. I must be doing something dumb, because now I'm getting a build error. I think this *might* be the important part: /usr/include/boost/detail/is_incrementable.hpp:59: error: no match for 'operator++' in '++boost::detail::is_incrementable_::impl<boost::shared_ptr<int> >::x' The 799B source file is here: http://mark.santaniello.net/files/hof2.cpp The 19KB error message is here: http://mark.santaniello.net/files/err.txt :) -Mark

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The fate of has_member?
by Sniv Le Flomp 21 Nov '05

21 Nov '05

Hi, What ever happened with has_member? I really need it. - Sniv

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Re: [Boost-users] program_options: wild write
by Merrill Cornish 21 Nov '05

21 Nov '05

Christian, If I put an unknown --option on the command line, I get an exception with an "unknown option" message, just as you would expect. If I omit --limit from the command line, then it gets defaulted to 1, just as it should. However, if I put --limit on the command line with an illegal value, say a string or a negative number rather than an unsigned int, then there is no exception message, even though I am catching std::exception& and (...) and printing a message for both. Instead, Dr Watson is called, apparently without triggering a C++ exception. Merrill

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lambda and shared_ptr?
by Mark Santaniello (AMD) 21 Nov '05

21 Nov '05

All, I'm trying to use lambda and shared_ptr together, but I'm running into a problem. Please see the code below. I'd like the lambda-generated functor to hold the shared_ptr by value, such that its ref count is incremented. This doesn't seem to be happening. Instead, the shared_ptr is deleted when foo() returns, resulting in undefined behavior. What am I doing wrong? Thanks, Mark #include <boost/lambda/lambda.hpp> #include <boost/function.hpp> #include <boost/shared_ptr.hpp> #include <iostream> using namespace std; using namespace boost::lambda; template< typename T > boost::function<T(T)> foo( T n_ ) { //Works, but leaks n //T *n = new T( n_ ); //Doesn't work boost::shared_ptr<T> n( new T(n_) ); return ( *n += _1 ); } int main() { // start with one boost::function<int(int)> accum = foo(1); cout << accum(2) << endl; cout << accum(10) << endl; // start with zero boost::function<int(int)> accum2 = foo(0); cout << accum2(6) << endl; cout << accum2(2) << endl; }

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Re: [Boost-users] Collections of shared_ptr<Base> and shared_ptr<Derived>
by Keith Weintraub 21 Nov '05

21 Nov '05

Folks, I have come up with the following solution in template form. I would be ecstatic to receive any feedback on either my solution or original question. I am not an expert in these things and I can use all the help any generous soul could provide. Here is my solution: // Function template to create a vector<shared_ptr<Base> >* from // a vector<shared_ptr<Derived> > template<typename Base, typename Derived> vector<shared_ptr<Base> > *derivedSharedPtrVectorToBase(vector<shared_ptr<Derived> > const &dVec) { vector<shared_ptr<Base> > *bVec = new vector<shared_ptr<Base> >(dVec.size()); for(int i = 0; i < dVec.size(); i++) (*bVec)[i] = dVec[i]; return(bVec); } Thanks for your time, KW ________________________________ From: Keith Weintraub Sent: Wednesday, November 16, 2005 10:17 AM To: 'boost-users(a)lists.boost.org' Subject: Collections of shared_ptr<Base> and shared_ptr<Derived> Folks, What is the best way to pass a std::vector<boost::shared_ptr<Derived> > to a function that expects a std::vector<boost::shared_ptr<Base> >? Can I use a cast or should I create a new std::vector<boost::shared_ptr<Base> > by iterating over the std::vector<boost::shared_ptr<Derived> >? Here is some sample code. What f is doing is not important it is just an example: class A { // This class is from a library I have no control over. public: virtual string getName() { return string("A");} }; class B : public A { // I need to create B from A to have extra functionality public: virtual string getName() { return string("B");} virtual string getLongName() { return string("This is B");} }; void f(std::vector<boost::shared_ptr<A> > &v) { // This function is from a library that I have no control over. for(int i = 0; i < v.size(); i++) cout << v[i]->getName(); } int main(char *argv, int arc) { std::vector<boost::shared_ptr<B> > bvec(10); boost::shared_ptr<B> bPtr(new B); bvec[0] = bPtr; f(bvec); // This should not compile. <------------------------- } The last line (with the arrow) won't compile because std::vector<boost::shared_ptr<B> > cannot be converted to std::vector<boost::shared_ptr<A> >.

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[BGL, Graph] add_vertex with specific ctor
by Johan Oudinet 21 Nov '05

21 Nov '05

Hello, I like the named parameter method to define graph properties, so all our properties are concentrated in a struct. But, I'd like add a vertex with specific properties are already defined: //======================= #include <iostream> #include <string> #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> using namespace std; using namespace boost; struct People { People () { } People (string const& n, int a) : name(n), age(a) { } string name; int age; }; int main(int, char**) { typedef adjacency_list< vecS, vecS, bidirectionalS, People > Graph; typedef graph_traits< Graph >::vertex_descriptor vertex_descriptor; Graph g; vertex_descriptor v; People n ("toto", 26); v = add_vertex (g); // this use the default ctor of People, a add_vertex(g, n) g[v] = n; // will be more efficiently (avoid a People assignment) cout << g[v].name << " is " << g[v].age << " old." << endl; } //======================= -- Johan

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Re: [Boost-users] Q: Graphs. Sorting edges. Possible? How to?
by Jeff Holle 21 Nov '05

21 Nov '05

I've found this partial solution for what I'm searching for. This code sorts by target, name. I want to sort by source, target. I find that in boost::graph adjacency_list edge descriptors there is a "get_target" method, but no "get_source" method. Can someone tell me how to either find the equivalent or give the comparison function object a non-default constructor so I can pass it a graph reference? Actually in the latter, I need assistance in feeding the graph reference to the graph object at construction time, not writing a constructor. Jeremy Siek wrote: > On Wed, 19 Jun 2002, stas_fomin wrote: > stas_f> > By using a custom container (use a std::set with your custom > stas_f> comparison > stas_f> > function) for the EdgeList type, you can get the out-edges of each > stas_f> vertex > stas_f> > sorted, but there currently is not a way to get the entire edge list > stas_f> > sorted. > stas_f> Ok... But BGL docs is less understandable (in comparison with > stas_f> LEDAbook) for me (I know I am stupid). > > Have you tried reading the BGL book? > > stas_f> So, please, show me small example of declaration > stas_f> of some graph with out_edges sorted according to some function... > > Here you go. Also, this example is checked into the libs/graph/example/ > directory. > > #include <boost/config.hpp> > #include <iostream> > #include <functional> > #include <string> > > #include <boost/graph/adjacency_list.hpp> > #include <boost/graph/properties.hpp> > > /* > Sample output: > > 0 --chandler--> 1 --joe--> 1 > 1 --chandler--> 0 --joe--> 0 --curly--> 2 --dick--> 3 --dick--> > 3 > 2 --curly--> 1 --tom--> 4 > 3 --dick--> 1 --dick--> 1 --harry--> 4 > 4 --tom--> 2 --harry--> 3 > > name(0,1) = chandler > > name(0,1) = chandler > name(0,1) = joe > > */ > > template <class StoredEdge> > struct order_by_name > : public std::binary_function<StoredEdge,StoredEdge,bool> > { > bool operator()(const StoredEdge& e1, const StoredEdge& e2) const { > // Order by target vertex, then by name. > // std::pair's operator< does a nice job of implementing > // lexicographical compare on tuples. > return std::make_pair(e1.get_target(), boost::get(boost::edge_name, > e1)) > < std::make_pair(e2.get_target(), boost::get(boost::edge_name, e2)); > } > }; > struct ordered_set_by_nameS { }; > > #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION > namespace boost { > template <class ValueType> > struct container_gen<ordered_set_by_nameS, ValueType> { > typedef std::multiset<ValueType, order_by_name<ValueType> > type; > }; > template <> > struct parallel_edge_traits<ordered_set_by_nameS> { > typedef allow_parallel_edge_tag type; > }; > } > #endif > int > main() > { > #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION > std::cout << "This program requires partial specialization" << > std::endl; > #else > using namespace boost; > typedef property<edge_name_t, std::string> EdgeProperty; > typedef adjacency_list<ordered_set_by_nameS, vecS, undirectedS, > no_property, EdgeProperty> graph_type; > graph_type g; > > add_edge(0, 1, EdgeProperty("joe"), g); > add_edge(1, 2, EdgeProperty("curly"), g); > add_edge(1, 3, EdgeProperty("dick"), g); > add_edge(1, 3, EdgeProperty("dick"), g); > add_edge(2, 4, EdgeProperty("tom"), g); > add_edge(3, 4, EdgeProperty("harry"), g); > add_edge(0, 1, EdgeProperty("chandler"), g); > > property_map<graph_type, vertex_index_t>::type id = get(vertex_index, > g); > property_map<graph_type, edge_name_t>::type name = get(edge_name, g); > > graph_traits<graph_type>::vertex_iterator i, end; > graph_traits<graph_type>::out_edge_iterator ei, edge_end; > for (boost::tie(i, end) = vertices(g); i != end; ++i) { > std::cout << id[*i] << " "; > for (boost::tie(ei, edge_end) = out_edges(*i, g); ei != edge_end; > ++ei) > std::cout << " --" << name[*ei] << "--> " << id[target(*ei, g)] << " > "; > std::cout << std::endl; > } > std::cout << std::endl; > > bool found; > typedef graph_traits<graph_type> Traits; > Traits::edge_descriptor e; > Traits::out_edge_iterator e_first, e_last; > > tie(e, found) = edge(0, 1, g); > if (found) > std::cout << "name(0,1) = " << name[e] << std::endl; > else > std::cout << "not found" << std::endl; > std::cout << std::endl; > > tie(e_first, e_last) = edge_range(0, 1, g); > while (e_first != e_last) > std::cout << "name(0,1) = " << name[*e_first++] << std::endl; > #endif > return 0; > } > > > > ---------------------------------------------------------------------- > Jeremy Siek http://php.indiana.edu/~jsiek/ > Ph.D. Student, Indiana Univ. B'ton email: jsiek(a)osl.iu.edu > C++ Booster (http://www.boost.org) office phone: (812) 855-3608 > ---------------------------------------------------------------------- > > >

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Boost::thread scheduling under HPUX
by Pete 21 Nov '05

21 Nov '05

Under heavy load, my HP-UX 11i application can run multiple, CPU intensive boost::thread's. Unfortunately, this has the side effect that other processes suffer in terms of performance. I initially thought that decreasing the nice value of my app would do the trick and ensure that other processes with a higher value would get priority by the kernel scheduler. However, this does not appear to be true (my app's nice value is 30 when most other processes run at 20). The requirement of my app is to run only whenever the system is idle. Is there a way this can be done using boost::thread or does anybody know how I could configure my process under HP-UX so that it behaves as intended?

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program_options: St9exception Exception?
by Merrill Cornish 21 Nov '05

21 Nov '05

I posted a question earlier about why I couldn't get Boost 1.33.0 program_options to "see" my positional parameter and why it bombed on unexpected options. Volodya pointed out that an illegal option throws an exception and asked if I had a catch. I felt like a fool for forgetting exceptions and through that was the problem. Then I looked at the code again. The method that uses program_options to read the command line had no try/catch, but the main program that called that method DID have the call wrapped in a try that has catches both for std::exception and (...). And yet, it wasn't trapping anything. Between ZoneAlert and Windows, I *think* I know the problem: something is attempting to access NULL, so I'm getting an OS memory error that C++ exceptions can't catch. I moved try's and catch's around in the code until I found the offending statement: po::variables_map vm; ...a declaration of all things. Here's an excerpt of the code po::options_description desc("Options"); desc.add_options() ("help,h", " Display this help message.") ("version", " Display the version.") // ... other options ;//add-options() // specify the single, required graph file positional parameter po::positional_options_description pd; pd.add("graph_file", 1); po::variables_map vm; //<============== try { po::store(po::command_line_parser(argc, argv). options(desc). positional(pd). run(), vm); po::notify(vm); // ... other code that references vm }//try catch(std::exception e) { cerr << "Exception:" << endl; cerr << e.what() << endl; exit(EXIT_FAILURE); }//catch catch(...) { cerr << "An unknown exception occurs while parsing : "command line arguments." << endl; exit(EXIT_FAILURE); }//catch Using the 'try' in the position shown above, if I input an unexpected command line options, an exceptioin is thrown whose what() method returns "St9exception". That's it. Just "St9exception". I can't find that string in the Boost source anywhere. However, if I move the "try" up one statement so it's above "po::variables_map vm;", then there's no exceptoin, but the access to location 0. That's one picky declaration. Merrill

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