January 2010 - Boost-users - lists.boost.org

Re: [Boost-users] boost any questions and praise
by Pete Bartlett 10 Feb '10

10 Feb '10

Alan Tennant wrote: >Thanks for the info. Can it be done (at all, at the moment, elegantly, practically, by turning a std::type_info into a type) ? Depending on exactly what you are trying to do, the Boost.Variant library may be more useful than Boost.Any.

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Boost Graph Lib > A*
by Damien Maupu 09 Feb '10

09 Feb '10

Dear all, First Hello. Then does anybody knows how the a star search works for implicit graph? There is little information on the Internet. I found a pdf: A* Graph Search Within the BGL Framework http://www.cs.rpi.edu/~beevek/research/astar_bgl04.pdf But I wasn't able to run the implicit graph example because I am missing: #include <nonconst_bfs.hpp> and #include "test-astar-visitors.hpp" #include "test-astar-accept.hpp" In the online doc: http://www.boost.org/doc/libs/1_40_0/libs/graph/doc/astar_search.html It is said to use astar_search_no_init but I don't know how. Any clues? Thank you Sincerely, Damien

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Serialization of a unordered_map
by Basti Korf 08 Feb '10

08 Feb '10

Hallo, I just wondered, why there is no possibility to serialize a unordered map. Since the STL map is serialized, i take the file for it and changed all maps to boost::unordered_map (multimap). Or is there a better way, i just did not see? Here is the code: #ifndef BOOST_SERIALIZATION_UNORDEREDMAP_HPP #define BOOST_SERIALIZATION_UNORDEREDMAP_HPP // MS compatible compilers support #pragma once #if defined(_MSC_VER) && (_MSC_VER >= 1020) # pragma once #endif /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8 // serialization/map.hpp: // serialization for stl map templates // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com . // Use, modification and distribution is subject to the Boost Software // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) // See http://www.boost.org for updates, documentation, and revision history. #include <boost/unordered_map.hpp> #include <boost/config.hpp> #include <boost/serialization/utility.hpp> #include <boost/serialization/collections_save_imp.hpp> #include <boost/serialization/collections_load_imp.hpp> #include <boost/serialization/split_free.hpp> namespace boost { namespace serialization { template<class Archive, class Type, class Key, class Compare, class Allocator > inline void save( Archive & ar, const boost::unordered_map<Key, Type, Compare, Allocator> &t, const unsigned int /* file_version */ ){ boost::serialization::stl::save_collection< Archive, boost::unordered_map<Key, Type, Compare, Allocator> >(ar, t); } template<class Archive, class Type, class Key, class Compare, class Allocator > inline void load( Archive & ar, boost::unordered_map<Key, Type, Compare, Allocator> &t, const unsigned int /* file_version */ ){ boost::serialization::stl::load_collection< Archive, boost::unordered_map<Key, Type, Compare, Allocator>, boost::serialization::stl::archive_input_map< Archive, boost::unordered_map<Key, Type, Compare, Allocator> >, boost::serialization::stl::no_reserve_imp<boost::unordered_map< Key, Type, Compare, Allocator > > >(ar, t); } // split non-intrusive serialization function member into separate // non intrusive save/load member functions template<class Archive, class Type, class Key, class Compare, class Allocator > inline void serialize( Archive & ar, boost::unordered_map<Key, Type, Compare, Allocator> &t, const unsigned int file_version ){ boost::serialization::split_free(ar, t, file_version); } // multimap template<class Archive, class Type, class Key, class Compare, class Allocator > inline void save( Archive & ar, const boost::unordered_multimap<Key, Type, Compare, Allocator> &t, const unsigned int /* file_version */ ){ boost::serialization::stl::save_collection< Archive, boost::unordered_multimap<Key, Type, Compare, Allocator> >(ar, t); } template<class Archive, class Type, class Key, class Compare, class Allocator > inline void load( Archive & ar, boost::unordered_multimap<Key, Type, Compare, Allocator> &t, const unsigned int /* file_version */ ){ boost::serialization::stl::load_collection< Archive, boost::unordered_multimap<Key, Type, Compare, Allocator>, boost::serialization::stl::archive_input_multimap< Archive, boost::unordered_multimap<Key, Type, Compare, Allocator> >, boost::serialization::stl::no_reserve_imp< boost::unordered_multimap<Key, Type, Compare, Allocator> > >(ar, t); } // split non-intrusive serialization function member into separate // non intrusive save/load member functions template<class Archive, class Type, class Key, class Compare, class Allocator > inline void serialize( Archive & ar, boost::unordered_multimap<Key, Type, Compare, Allocator> &t, const unsigned int file_version ){ boost::serialization::split_free(ar, t, file_version); } } // serialization } // namespace boost #endif // BOOST_SERIALIZATION_UNORDEREDMAP_HPP Best regards, SK -- GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT! Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01

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Standard error handler in gil jpeg_io extension calls exit()
by Peter Goetz 06 Feb '10

06 Feb '10

Hi, I'm using the gil jpeg_io extension like this: gil::rgb8_image_t img; gil::jpeg_read_image("test.jpg",img); As it turned out, if "test.jpg" is not a jpeg the program will quit with the message: "Not a JPEG file: starts with 0x6b 0x6a" although I put a try-catch-block around it. Digging a bit deeper, I found, that this is because in boost/gil/extension/io/jpeg_io_private.hpp the jpeg_reader::init() function uses the standard error handler: _cinfo.err=jpeg_std_error(&_jerr); which calls the exit() function. I'd prefer to have an exception and handle the exception in my main program rather than in the library. Is there a way to do that? To me it seems there's no other way than modifying the jpeg_io_extension. Or am I missing something? Any help is very appreciated! Peter

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multi_array: how can I efficiently have a column selected?
by petros mamales 04 Feb '10

04 Feb '10

Hi, I am a real newbie here, so please excuse the naivity of the question. I, say, have a 3d array (fortran storage), and want to create a view to it so that I select say: grid[ indices[ [range(9,10)] [3], [range(9,10)] ]; I am not clear on exactly what this creates: from the documentation, I see this creating a 3d view. Can I use stl-like iterators on this, to use stl type algorithms? Is there any other repository of examples that would use high-level constructs like this so that I could look into a few examples? Again, I apologize for the bredth of the question. Best Regards, Petros

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wait/notify problem
by girish hilage 03 Feb '10

03 Feb '10

Hi, I am trying to implement MANAGER:WORKER model using boost thread_group. I am using wait() and notify() for that. In my application, when thread1 wants to listen for some event from thread2, it executes wait(). when thread2 wants to inform about the event to thread1, it executes notify(). The problem I am facing is : thread1 first executes wait(). then thread2 executes notify(). but notify() completes its execution even before thread1 actually starts waiting for the event and notify() is goes in vain and then thread1 keeps on waiting infinitely. To avoid this, right now I am using sleep(1) before thread2 calls notify() to make sure that thread1 really reaches the actual wait state. But this is not a permanent solution; as it is possible that even within 1sec thread1 might not actually start listening for the event. (Also 1sec makes my applcation very slow). So, I just want to know if there is any such mechanism which will enable thread2 to keep notify()ing until the event is accepted by thread1? i.e. blocked notify(). Regards, Girish

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boost any questions and praise
by Alan Tennant 02 Feb '10

02 Feb '10

Firstly. Thank you very much team Boost, it looks like it will be very useful and solve many of my coding problems. I can create an any boost::any a1; I can assign something to it a1 = string1; I can get it back out later std::cout<<any_cast<std::string>(a1); A boost any has a "type()" method. However this produced an error. std::cout<<any_cast<a1.type()>(a1);

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[multi_array] deduce logical shape of "parent" multi_array from view
by alfC 02 Feb '10

02 Feb '10

Hi, I am programming and adaptor of the HDF5 library to handle, to some extend, multi_arrays in an elegant way. It turns out that when I try to save a multi_array_view, with strides and offsets, etc. HD5F still needs to know the logical size (shape) of the parent array (the one that has contiguous elements in memory). The paradox is that in order to save an array view I need to know the original array. The question is, is there an (elegant) way to reconstruct the shape of the original array just from the multi_array_view. For moments it seems imposible because array_view doesn't know even the dimensionality of the "parent" array (or it does?). The task is further complicated because many members that may have this information are actually private or protected within multi_array_view. This is an example of what I want: multi_array<2> A(extents[10][10]); multi_array_view<1> Aview = A[3][indeces[range(0,10,2)]]; desired_function(Aview); --> returns 10, 10. Thanks, Alfredo

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boost::random: get same number sequences 32/64 bit?
by Sebastian Mach 01 Feb '10

01 Feb '10

Hello list, today I found out that boost::random, at least the combination boost::mt19937 rng(<seed>); typedef boost::uniform_int<int> dist_t; dist_t dist (<min>, <max>); boost::variate_generator< boost::mt19937&, dist_t > rand_ (rng, dist); will give me different results depending on whether I use "g++ (Debian 4.3.2-1.1) 4.3.2" (with sizeof(long)=8) or "g++.exe (TDM-2 mingw32) 4.4.1" (with sizeof(long)=4). This testcase: ++ #include <boost/random.hpp> boost::mt19937 rng(1); typedef boost::uniform_int<int> dist_t; dist_t dist (0, 16); boost::variate_generator< boost::mt19937&, dist_t > rand_ (rng, dist); int main () { for (int i=0; i<6; ++i) { std::cout << rand_() << std::endl; } } -- will print 16 8 1 6 0 12 with the 64bit variant variant, but 7 16 12 15 0 2 with the 32bit variant. Is there a (preferably portable) way to ensure that they will be the same on all 32bit+ machines? Otherwise this would be a real stopper to use boost::random for me, and I'd have to go back to libcoyotl's Mersenne Twister, which gives consistent results, upon which I really depend. Sincerely Sebastian Mach phresnel(a)gmail.com

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[range_ex]"Practical" Status of boost::range, boost::range_ex, and associated algorithms
by Jesse Perla 01 Feb '10

01 Feb '10

Hi there, I am excited to start using ranges in user code with standard algorithms (mostly copy, transform, binary_searches). Is it safe for me to start using code with range/range_ex? Since the http://www.boostpro.com/vault/index.php?directory=Algorithms version hasn't been updated for a while, I was worried that there could be interface changes. I am perfectly willing to use a subset of algorithms that are expected to remain stable -Jesse

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