August 2010 - Boost-users - lists.preview.boost.org

[DateTime] from time_t to ptime and back - or not
by Christoph Duelli 23 Aug '10

23 Aug '10

[I am using Boost 1.43.0 on linux, gcc 4.4.1] I am having trouble with date_time's ptime. I am passing it a time_t, and store that in a ptime object. When I retrieve the time_t, I am getting a different value than the one I passed to it originally. (the difference seems to be 2 hours - in all probability due to UTC vs local time issues). Code: time_t now = time(NULL); boost::posix_time::ptime pt = boost::posix_time::from_time_t(now); struct tm tm = to_tm(pt); time_t should_be_now = mktime(&tm); BOOST_CHECK_EQUAL(now, should_be_now); fails for me: now is by 7200 seconds (i.e. 2 hours) ahead of. Is this a bug in date_time or am I just failing to use it properly? Thank you, and best regards Christoph

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[bind]Help! Can we modify parameters before pass them into bind (see the context below for details)
by jungleman 23 Aug '10

23 Aug '10

Hi, I have some problems on function template bind. the original usage of bind is : bind(func, _1, _2), and I wonder whether I can modify the parameters before pass them into bind, for example, functype function = bind(func, *_1, *_2). So that, when I use function(a, b), it will do like this: func(*a, *b). May it work, or some way else to do this? I just wanna do this in one line code. thanks in advance. -- Stay hungry, stay foolish !

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Boost.Intrusive issues on IBM compiler
by Jeremiah Willcock 22 Aug '10

22 Aug '10

It appears that almost all of the Boost.Intrusive tests (at <URL:http://tinyurl.com/2bzhglh>, for example) fail on IBM's compiler. I get similar results, like the following from the test suite, from my own code: An expression of type "overloaded function: U::to_node_ptr" cannot be converted to type "boost::intrusive::list_node<void *> *(boost::intrusive::detail::base_hook_traits<boost::intrusive::testvalue<hooks<void *>,0>,boost::intrusive::list_node_traits<void *>,1,boost::intrusive::default_tag,1>::*)(testvalue<hooks<void *>,0> &)" Is there an easy workaround for this issue? Is there a plan to fix it? This has also been reported a couple of months ago as bug 4412 (<URL:https://svn.boost.org/trac/boost/ticket/4412>). Thank you. -- Jeremiah Willcock

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axpy_prod Weirdness
by Jane Shevtsov 22 Aug '10

22 Aug '10

I have a little program that implements an ecological network analysis algorithm. (It looks at the importance of indirect energy or matter flows between species.) 01 //dea.cpp -- The fundamental DEA algorithm 02 03 #include <boost/numeric/ublas/matrix.hpp> 04 #include <boost/numeric/ublas/operation.hpp> 05 #include <boost/numeric/ublas/io.hpp> //for test 06 #include "storage_adaptors.hpp" //for test 07 08 using boost::numeric::ublas::matrix; 09 10 void dea(const matrix<double>[], int, int, matrix<double>[]); 11 matrix<double> indflow(const matrix<double> & Ndea, const matrix<double> & Gdea); 12 13 int main() { 14 using boost::numeric::ublas::make_matrix_from_pointer; 15 matrix<double> Garr[4]; 16 matrix<double> Narr[2]; 17 double G1[3][3] = {0, 0, 0, 0.33333, 0, 0, 0.66667, 1, 0}; 18 double G2[3][3] = {0, 0, 0, 0.6, 0, 0, 0.4, 1, 0}; 19 double G3[3][3] = {0, 0, 0, 0.55, 0, 0, 0.45, 1, 0}; 20 double G4[3][3] = {0, 0, 0, 0.5, 0, 0, 0.5, 1, 0}; 21 Garr[0] = make_matrix_from_pointer(G1); 22 Garr[1] = make_matrix_from_pointer(G2); 23 Garr[2] = make_matrix_from_pointer(G3); 24 Garr[3] = make_matrix_from_pointer(G4); 25 dea(Garr, 2, 4, Narr); 26 std::cout << Narr[0] << std::endl; 27 matrix<double> ratio = indflow(Narr[0], Garr[0]); 28 std::cout << ratio << std::endl; 29 return 0; 30 } 31 32 //The fundamental DEA algorithm 33 //Takes array of G matrices, window size, array length and empty array for N_DEA matrices as input 34 void dea(const matrix<double> Garr[], int win, int arrLen, matrix<double> Narr[]) { 35 using namespace boost::numeric::ublas; 36 int matSize = Garr[0].size1(); 37 for (int i = 0; i < arrLen - win; i++) { 38 matrix<double> Gprod = identity_matrix<double>(matSize); 39 Narr[i] = identity_matrix<double>(matSize); 40 //the core loop 41 for (int j = 0; j < win; j++) { 42 Gprod = prod(Gprod, Garr[i+j]); 43 Narr[i] += Gprod; 44 } 45 } 46 } 47 48 //computes indirect flow fraction 49 matrix<double> indflow(const matrix<double> & Ndea, const matrix<double> & Gdea) { 50 using namespace boost::numeric::ublas; 51 int matSize = Ndea.size1(); 52 matrix<double> iflow = Ndea - Gdea - identity_matrix<double>(matSize); //Ind = N-G-I 53 matrix<double> frac = zero_matrix<double>(matSize, matSize); //inialize indirect flow fraction matrix 54 //perform division for nonzero, off-diagonal elements 55 for (int i=0; i<matSize; i++) { 56 for (int j=0; j<matSize; j++) { 57 if (i != j && Ndea(i,j) != 0) //avoid division by zero 58 frac(i, j) = iflow(i, j) / Ndea(i, j); 59 } 60 } 61 return frac; 62 } The correct output is below. [3,3]((1,0,0),(0.33333,1,0),(1.26667,1,1)) [3,3]((0,0,0),(0,0,0),(0.473683,0,0)) The code given above works, but to speed it up, I tried replacing the first line of the core loop in dea() with axpy_prod(Gprod, Garr[i+j], Gprod, true);. This gives the following wrong output: [3,3]((1,0,0),(0,1,0),(0,0,1)) [3,3]((0,0,0),(0,0,0),(0,0,0)) And if I use axpy_prod(Gprod, Garr[i+j], Gprod, false);, I get: [3,3]((3,0,0),(1.26666,3,0),(2.33334,3,3)) [3,3]((0,0,0),(0.736843,0,0),(0.714285,0.666667,0)) What gives? When should I avoid using axpy_prod? -- ------------- Jane Shevtsov Ecology Ph.D. candidate, University of Georgia co-founder, <www.worldbeyondborders.org> Check out my blog, <http://perceivingwholes.blogspot.com>Perceiving Wholes "The whole person must have both the humility to nurture the Earth and the pride to go to Mars." --Wyn Wachhorst, The Dream of Spaceflight

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[bind]Help! Can we modify parameters before pass them into bind (see the context below for details)
by jungleman 22 Aug '10

22 Aug '10

Hi, I have some problems on function template bind. when I uses stl algorithm adjacent_find(inputIterator begin, inputIterator) -- Stay hungry, stay foolish !

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[asio] Feature request for serializable types.
by Germán Diago 22 Aug '10

22 Aug '10

Hello. I'm using boost.asio and trying to serialize a boost.variant, which is serializable because each of the fields I used in the variant have a serialize method required by boost.serialization library. I want to send my variant as binary data. This is not easy although I have a serialize method because this does not work: async_write(mysocket, boost::asio::buffer(myserializablevariant), when_done); I think all serializable types should be automatically usable as boost::asio::buffer, like std::vector, in this call. I think this shouldn't be too hard to implement, but I don't know how to serialize my data in binary format in a straight-forward way. Any ideas? Thanks in advance.

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thread-safe initialization for singleton
by Kraus Philipp 22 Aug '10

22 Aug '10

Hi, I have written a class with static methods and properties. Now the class must be used in a multithreaded environment, so I get some race conditions error. I use boost::thread for implementating the threads. I have found boost_once but I don't know how to use it, so my class properties are initialized once. Thanks Phil

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multiple serialized objects to same file
by Oscar Pernas 21 Aug '10

21 Aug '10

Hi! I know that this question is asked before but I cant see any answer about it. Is posible with boost serialization to write different objects to the same file? if is possible, is possible to access to each object with an iterator or with position like binary files? thanks -- Óscar Pernas Plaza.

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[BGL] segFault
by John Robertson 21 Aug '10

21 Aug '10

I'm trying to obtain an iterator of edges with a different ordering than that given in egdes(g). The following compiles but segfaults at std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() ); (runs ok if the above line is commented out) //////////////////////////////////////////////////////////////////////////////////////////////////////////////// typedef Traits::edge_descriptor edd; // Create ordering template < typename Graph, typename edd > struct ordering { Graph & g; bool operator ()(const edd & a, const edd & b) { return g[a].eName < g[b].eName; } }; template < typename Graph > int initialize_container( Graph & g ) { typename graph_traits<Graph>::edge_iterator edge_iter, edges_end; // create vector of edge descriptors. std::vector< Traits::edge_descriptor > VE(num_edges(g)+1); int i = 1; // (Sometimes I like to start at 1.) //insert edge descriptors into vector of edge descriptors. for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end; ++edge_iter) { cout << " *edge_iter = " << *edge_iter << endl; VE[i++] = *edge_iter; } // segfaults here //sort vector of edge descriptors. std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() ); //print sorted edge descriptors. for( int i = 1; i < num_edges(g)+1; ++i ) cout << " -Edge " << i << " = " << VE[i] << endl; } Thanks

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[BGL] Updating the source vertex of an edge in-place
by Daniel Trebbien 21 Aug '10

21 Aug '10

I need to be able to update the source vertex of an edge in-place. The only option that I see is to remove the edge with `remove_edge` and then add a new edge with `add_edge`. The problem, however, is that I think this will mess up a property map of an edge property if it cannot expand to map a new value for the newly-added edge. Thus, I would like to update the edge in-place. How do I do this?

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