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[BGL] implementing operator < for edge_descriptors
by Max Schoebinger 02 Feb '05

02 Feb '05

Hello, I am trying to create a std::map<edge_descriptor, unsigned int>. Unfortunaltely, there is no less operator defined for edge descriptors, so i'd like to implement my own version based on a custom internal property associated with the edge. Is it possible to access an arbitrary property, solely based on an edge_descriptor without having access to the graph object? Here some pseudo-code: struct compare_edge_descriptors { bool operator()(edge_descriptor e1, edge_descriptor e2) { unsigned int val1 = get_property_somehow(e1.get_property(), my_custom_property); unsigned int val2 = get_property_somehow(e2.get_property(), my_custom_property); return (val1 < val2 ); } }; Do you have an idea how to implement "get_property_somehow"? Thanks, Max

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boost-users: cant i use mpl::contains to find members of list_c ??
by suresh.t＠philips.com 02 Feb '05

02 Feb '05

hi, I was trying to use mpl::contains with list_c and it always seems to return mpl::false_. For example typedef mpl::list_c< int ,16,8 > mylist; typedef mpl::contains<mylist, mpl::int_<16> >::type tt; "tt::value" is zero though i thought 16 being in the mylist it would be 1. Can someone please let me know whether the usage is improper and if so what should be used to find elements in list_c? Thanks in Advance S.T

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Exercices 3-3 and 3-4 (C++ Templates Metaprogramming)
by Philippe Mori 02 Feb '05

02 Feb '05

I'm not sure of the meaning of "twice twice" and "twice on itself" respectively. My guess would be for exercice 3 that I should do something like : typedef twice<to_be_filled_1>::type T1; // T1 would be T ** // The second time, I replace T (in to_be_fiiled_1) by // T1 (in to_be_filled_2) , thus T2 is T1** which is also T**** typedef twice<to_be_filled_2>::type T2; while for exercice 4, we want something that would look like : typdef twice<twice<to_be_filled_3a>to_be_filled_3b>::type T3; Does I understand the questions correctly? For twice, I use the definition from section 3.3.2. Philippe

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Exercice 3-7 (C++ Templates Metaprogramming)
by Philippe Mori 02 Feb '05

02 Feb '05

I do not understand well the semantic of some constructs. 1) For t1, does the external mpl::lambda has any effect on some use of t1 or mpl::lambda<_1>::type and also mpl::lambda<_1> are always equivalent? 2) Does the uses of lambda in t8 has any effect or the result is always the same as with t2. 3) Does there are other tests that the ones below (i to vii) that would shows some other differences in the semantics of the expression? 4) Same question but for to_be_filled part of my tests. Anything different that the four ones belows (a to d)? 5) In any ot the tests with a to_be_filled part, is it possible to have more than one template argument and that the extra ones are used? The thing I have some of the following (what I have tried and what compile depends on the construct - that is t1, t2,...) : i) display_type(tn); ii) display_type(tn::type); iii) display_value(tn::type::value); iv) display_type(mpl::apply<tn, to_be_filled>::type) v) display_value(mpl::apply<tn, to_be_filled>::type::value) vi) display_type(tn::apply<to_be_filled>::type) vii) display_value(tn::apply<to_be_filled>::type::value) where tn is one of the type t1, t2,... t8 and to_be_filled is something similar to one of those : a) int b) X where X is a metafunction class c) mpl::plus<int_<1>, int_<2> > d) Y where Y is a simple metafunction similar to always_int in section 3.5.4. I have look at the documentation but it is hard to see the relation between each construct, the possible uses of each ones and their prmary purpose. I would be nice to provide more samples and more equivalences. Philippe

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uBLAS sparse_matrix "default" value
by Austin Bingham 02 Feb '05

02 Feb '05

Apparently the wheels of the ublas mailing list move slowly, so I'm asking this question here. Is there any way to set the "default" value of a sparse_matrix? sparse_matrix seems to guarantee that you always get a value when you access an index, even if that index hasn't been explicitly set. For sparse_matrix<float>, for instance, you get 0. Is there any way to specify this value? That is, if I wanted to get back, say, -1 for unset entries, is there a way to do this? There's no direct mention of this that I can find, although there were some discussions of zero-constructors or somesuch that may have been dealing with this question. Thanks. Austin Bingham

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mpl -> integral sequence wrappers -> wrapping enums ?
by Martin Pasdzierny 02 Feb '05

02 Feb '05

Hello MPL experts, I'd like to use meta - vectors of integral constants defined as enums. But unfortunately the code below does not compile. <code> #include <iostream> #include <boost/mpl/vector_c.hpp> #include <boost/mpl/size.hpp> enum MY_ENUM {X,Y}; // (*) typedef boost::mpl::vector_c<MY_ENUM,X,Y> my_vector_c; static const int size = boost::mpl::size<my_vector_c>::value; int main(int argc, char** argv) { std::cout << "\nsize:" << size << "\n... bye" << std::endl; } </code> After replacing line (*) with typedef boost::mpl::vector_c<int,X,Y> my_vector_c; the code compiles and runs fine, but this does not look type safe any more. Any suggestions ?! regards, Martin.

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Re: Rationale for intrusive_ptr?
by Brian Neal 02 Feb '05

02 Feb '05

Well to answer my own question, I think, it can be used when you already have something that is reference counted and you want to manage it yourself. Also in places where new and delete aren't the correct actions. Or when you need something with less resource requirements than shared_ptr. For example, when multi-threading is turned on, shared_ptr asks for a mutex. Intrusive_ptr leaves that up to you. Am I getting close here? I didn't think about using it when you have a function that takes a shared_ptr but you need to pass in this. I dunno, I tend to use shared_ptr sparingly. If I don't need a shared_ptr, I don't ask for one on the interface to a function. That way the user can pass in a naked pointer or a shared_ptr::get(). I make sure to document what the function does (and does not do) with the input pointer though. Thanks. __________________________________ Do you Yahoo!? Yahoo! Mail - Find what you need with new enhanced search. http://info.mail.yahoo.com/mail_250

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equality fails with C++ bools
by Ross Boylan 02 Feb '05

02 Feb '05

I have a function declared bool that is acting rather non-bool. std::cout << obj.fn() gives me "76" and BOOST_CHECK_EQUAL(obj.fn), true) fails, with the message /home/ross/peter/R/mspath/src/test/Covariates_test.cc(178): error in "obs_covariates": test env.matchesObservation() == true failed [76 != 1] std::cout << true prints "1". obj.fn() works OK as an argument to if (obj.fn()). I am using g++ 1:3.3.5-5 on Debian GNU/Linux. I've tried -O2 and -O1; same behavior either way. boost is 1.31.0-9 The function is declared bool matchesObservation() const Maybe bool is being typedef'd or #define'd to int somewhere, for compatibility with old code? Probably not; I tried printing typeid(xxx).name() and got "b" for true and the function return value, while I got "i" for the number 1. I tried tracing into the code with limited success. Some mix of the fact that the underlying libraries weren't a debug version, that the code was optimized, and that there are #line directives (the source files were generated out of another file) made it hard to follow. Any suggestions? -- Ross Boylan wk: (415) 502-4031 530 Parnassus Avenue (Library) rm 115-4 ross(a)biostat.ucsf.edu Dept of Epidemiology and Biostatistics fax: (415) 476-9856 University of California, San Francisco San Francisco, CA 94143-0840 hm: (415) 550-1062

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Christoph Jaeschke/Germany/IBM is out of the office.
by Christoph Jaeschke 02 Feb '05

02 Feb '05

I will be out of the office starting 02/02/2005 and will not return until 02/09/2005. I will respond to your message when I return.

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Compilation Error
by Grek 01 Feb '05

01 Feb '05

Hi: I am a newbie to the world of Boost. I have a problem in compiling a program. I do not know how to set the path to compile the attached code. My platform is Cygwin gcc version 3.3.3 The boost_1_32_0 subdirectory resides in the Cygwin directory. I tried the following, g++ boost_1_32_0/boost/graph/sourcecode.cpp and it displays the message boost/config.hpp : No such file or directory boost/graph/graph_traits.hpp : No such file or directory boost/graph/adjacency_list.hpp : No such file or directory boost/graph/dijkstra_shortest_paths.hpp : No such file or directory followed by more error messages. Please refer to the attached code and help me out. Thanks in advance. Sourcecode.cpp ****************************************************************************** #include <boost/config.hpp> #include <iostream> #include <fstream> #include <string> #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/dijkstra_shortest_paths.hpp> using namespace boost; float maximum(float a[], float mx, int n){ float max=mx; for(int i=0; i<n; ++i){ if(max < a[i]){ max=a[i]; } } return max; } int main() { int num_nodes = 10000; int num_PPIs = 50000; char node[num_nodes][10], p1[num_PPIs][10], p2[num_PPIs][10]; char name[num_nodes]; float wt[num_PPIs], apl, dia, path[num_nodes]; int i, j, l, l1, l2, mx_len=num_nodes, pl[mx_len]; typedef adjacency_list < listS, vecS, directedS, no_property, property < edge_weight_t, float > > graph_t; typedef graph_traits < graph_t >::vertex_descriptor vertex_descriptor; typedef graph_traits < graph_t >::edge_descriptor edge_descriptor; typedef std::pair<int, int> Edge; std::ifstream INF1 ("./data/None.conversion"); std::ifstream INF2 ("./data/None.before"); if(!INF1){ std::cerr << "Cannot find INF1 file." << std::endl; return EXIT_FAILURE; } if(!INF2){ std::cerr << "Cannot find INF2 file." << std::endl; return EXIT_FAILURE; } //read data i=0; while(INF1 >> num_nodes >> node[i]){ ++i; } INF1.close(); num_nodes=i; i=0; while(INF2 >> p1[i] >> p2[i] >> wt[i]){ wt[i]=1.0; ++i; } INF2.close(); num_PPIs=i; // Edge edge_array[num_PPIs]; for(i=0; i<num_PPIs; ++i){ for(j=0; j<num_nodes; ++j){ if(stricmp(p1[i],node[j]) == 0){ edge_array[i].first=j; } } for(j=0; j<num_nodes; ++j){ if(stricmp(p2[i],node[j]) == 0){ edge_array[i].second=j; } } } // int num_arcs = sizeof(edge_array) / sizeof(Edge); std::cout << "0 None " << num_PPIs << " " << num_nodes; graph_t g(edge_array, edge_array + num_arcs, wt, num_nodes); property_map<graph_t, edge_weight_t>::type weightmap = get(edge_weight, g); std::vector<vertex_descriptor> p(num_vertices(g)); std::vector<float> d(num_vertices(g)); // l1=0; l2=0; dia=0; for(j=1; j<mx_len; ++j){ pl[j]=0; } // for(int src=0; src<num_nodes; ++src){ vertex_descriptor s = vertex(src, g); dijkstra_shortest_paths(g, s, predecessor_map(&p[0]).distance_map(&d[0])); for(j=0; j<num_nodes; ++j){ if(j == p[j]){ //set self-looping node to zero distance d[j]=0; } if(d[j] > 10000){ //set non-connecting node to zero distance d[j]=0; } path[j]=d[j]; pl[int(d[j]+0.5)]=pl[int(d[j]+0.5)]+1; } dia=maximum(path,dia,num_nodes); } for(l=1; l<=int(dia); ++l){ l1=l1+pl[l]*l; l2=l2+pl[l]; } apl=float(l1)/float(l2); std::cout << " " << apl << " " << l1 << " " << l2 << " " << dia << std::endl; return EXIT_SUCCESS; } ********************************************************************************** Cheers Grek --------------------------------- Do you Yahoo!? Yahoo! Search presents - Jib Jab's 'Second Term'

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