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boost::graph, ref vs. copy during relaxation
by Tristram Gräbener 27 Aug '12

27 Aug '12

Hello, I use boost::graph and the Dijkstra algorithm. My edge property is rather big (I store public transport timetables on them). In the file boost/graph/relax.hpp, the property of an edge is copied : W w_e = get(w, e); As my properties are large, it yields some overhead. I changed that line to const W & w_e = get(w, e); My benchmarks (on 1000 runs) went from 101 secs down to 87 (using GCC 4.6 -O3) So my question is : – would it hurt if it used const& instead of copy? – am I not correctly using the lib? Maybe should I use an index on the edge property and use a functor to get the data in the different operations (edge_less, combine); but wouldn't it mean re-implementing the properties? Thank you for your help

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simultaneous async_read_some and async_write using strand
by Chris Stankevitz 27 Aug '12

27 Aug '12

Hello, Q1: If I call async_write while there is a pending async_read_some in a single-threaded environment, can the write complete before the read completes? (i.e. will I need to receive some data before the write goes out?) Q2: Same question, but if I am using strand to serialize the operations. Thank you, Chris

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Boost graph issues with Xcode 4.4
by Jon McCormack 27 Aug '12

27 Aug '12

Hello, I'm trying to use boost 1.51 graph library with Xcode 4.4 and running into problems. While boost will build fine, when I try some simple graph code as per the documentation: #include <iostream> // for std::cout #include <utility> // for std::pair #include <algorithm> // for std::for_each #include <boost/graph/graph_traits.hpp> #include <boost/graph/adjacency_list.hpp> #include <boost/graph/dijkstra_shortest_paths.hpp> using namespace boost; int main(int,char*[]) { // create a typedef for the Graph type typedef adjacency_list<vecS, vecS, bidirectionalS> Graph; ...etc. I get the following errors: In file included from graph.cpp:4: In file included from /usr/local/include/boost/graph/graph_traits.hpp:26: In file included from /usr/local/include/boost/pending/property.hpp:13: In file included from /usr/local/include/boost/type_traits.hpp:35: In file included from /usr/local/include/boost/type_traits/has_operator.hpp:12: In file included from /usr/local/include/boost/type_traits/has_bit_and.hpp:43: /usr/local/include/boost/type_traits/detail/has_binary_operator.hpp:220:1: error: C++ requires a type specifier for all declarations BOOST_TT_AUX_BOOL_TRAIT_DEF3(BOOST_TT_TRAIT_NAME, Lhs, Rhs=Lhs, Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::trait_impl < Lhs, ... ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ /usr/local/include/boost/type_traits/detail/has_binary_operator.hpp:220:30: error: use of undeclared identifier 'has_bit_and' BOOST_TT_AUX_BOOL_TRAIT_DEF3(BOOST_TT_TRAIT_NAME, Lhs, Rhs=Lhs, Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::trait_impl < Lhs, ... ^ /usr/local/include/boost/type_traits/has_bit_and.hpp:12:29: note: expanded from macro 'BOOST_TT_TRAIT_NAME' #define BOOST_TT_TRAIT_NAME has_bit_and ^ In file included from graph.cpp:4: In file included from /usr/local/include/boost/graph/graph_traits.hpp:26: In file included from /usr/local/include/boost/pending/property.hpp:13: In file included from /usr/local/include/boost/type_traits.hpp:35: In file included from /usr/local/include/boost/type_traits/has_operator.hpp:12: In file included from /usr/local/include/boost/type_traits/has_bit_and.hpp:43: /usr/local/include/boost/type_traits/detail/has_binary_operator.hpp:220:230: error: expected ';' after top level declarator ...Lhs, Rhs=Lhs, Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::trait_impl < Lhs, Rhs, Ret >::value)) The errors continue for a number of type_traits/detail files. Is this an issue with clang? Thanks, Jon

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how to find a point from linestring?
by rakesh patil 27 Aug '12

27 Aug '12

Hi, I am new to Boost. I am using boost::geometry to define my data structure as follows typedef boost::geometry::model::point<double, 3, bg::cs::cartesian> point_3d; typedef boost::geometry::model::linestring<point_3d> linestring_3d; and I declare a linestring variable as follows linestring m_linestring; Now after adding several points in m_linestring, is there any way to find out whether a particular point exists in the list m_linestring? Just like in case of std::vector, it can be found out using std::find function. Thanks in advance

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Re: [Boost-users] seed for pseudo-random generator
by Neil Nelson 26 Aug '12

26 Aug '12

For a little more entropy you can add the seconds from time to the process PID (UUID). That will give you a difference each run at the seconds numeric scale that would tend to repeat at the PID cycle rate. You could add in microseconds from http://www.boost.org/doc/libs/1_51_0/doc/html/date_time/posix_time.html (Linux gettimeofday) for additional entropy. On Linux with some additional work you can use /dev/random and /dev/urandom (better). Neil Nelson > I create within a class the MT object with > > static boost::mt19937 m_random; > > so I need for a static variable for the initialization value, so I do this with > > boost::mt19937 tools::random::m_random( time(NULL) );= > > Now: My question is, can I use the time() value for initialization the MT object, so that the MT object returns values with a good entropie or > should I need another initialization value like a UUID of the OS? > > Because the time function (http://www.cplusplus.com/reference/clibrary/ctime/time/ ) returns a time_t value, so is this value good for initialization or should I need another value, if yes, which value if a good choice for > initialize the MT object?

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seed for pseudiorandom generator
by Kraus Philipp 26 Aug '12

26 Aug '12

Hello, I'm updating some algorithms and I need a tip for initialisation of the boost mersenne twister. I think the ctime is not a very good initialization. I think about a uuid value of the OS. I use also the non-deterministic generator, but I need an idea for the mersenne twister initialization. Do you have an idea? Thanks Phil

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Re: [Boost-users] Announce: Boost 1.51 installer for 32/64-bit Windows now available
by niXman 26 Aug '12

26 Aug '12

2012/8/24 niXman: > Why not to add libraries for MinGW? ping? -- Regards, niXman ___________________________________________________ Dual-target(32 & 64 bit) MinGW compilers for 32 and 64 bit Windows: http://sourceforge.net/projects/mingwbuilds/

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Re: [Boost-users] asio HTTP Server 3 example memory leak
by admin＠thefireflyproject.us 25 Aug '12

25 Aug '12

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Boost 1.44.0 with Python 2.7.1
by Sunil Thomas 25 Aug '12

25 Aug '12

Hi! I've built and installed successfull Python 2.7.1 that I've separately tested for an application with a boost-1.45.0 build that I also installed successfully. But for another application, I needed to build and install boost-1.44.0 and here I also I've been able to build/install boost successfully using the documentation (bootstrap/bjam after specifying prefix and with-python arguments). But when I build the (C++) application which invokes *Py_Init(...)*, I am getting the following error: *Linking CXX executable ../../../myapp_exec ../../../../../config/cmake/platforms/../../../../3rdparty/2012/package/rh5_x86_64_gcc-4.1.2/boost-1.44.0/lib/libboost_python-gcc41-1_44.so: undefined reference to `Py_InitModule4' collect2: ld returned 1 exit status gmake[2]: *** [myapp_exec] Error 1 * I am completely stuck here and would greatly appreciate any ideas to help understand and try to resolve this. I can easily do another boost-1.44.0 build with an older version of python to see if that helps. Thanks in advance for your time and please let me know if you have any questions. Thanks, -Sunil.

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Can we tell the version of Python used from boost-python pre-compiled library?
by Sunil Thomas 24 Aug '12

24 Aug '12

Hi! As the subject indicates, would appreciate, if someone can let me know how we can figure out the version of Python used in building a pre-compiled boost-python library? Thanks, -Sunil

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