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

Polymorphic serialization with polymorphic archives problems... [part 2]
by Bogdan 03 Nov '10

03 Nov '10

First I would like to confirm I tested Robert Ramey's fix (@60273) for multiple registrations and it looks good in my runs. Thank you Robert! On the other hand, I am under the impression there is a bug in void_caster::recursive_unregister(), although I am not 100% certain about the reason: that function member is called in the destructors of the void caster template classes and makes use of the void_caster_registry singleton (more specifically the type_set). I believe it searches the set for all the void caster entries that are descendants of the current one (i.e., the one being destroyed) and performs the following ops: - delete the shortcuts. - remove the corresponding entries from the set. However, void_caster::recursive_unregister() DOESN'T REMOVE FROM THE REGISTRAR the entry corresponding to the current void_caster(). This creates the problem below: consider a scenario where a dll containing some serialization functionality is loaded explicitly at runtime (i.e., using LoadLibrary() on Windows or dlopen on Unix). There are no parent-child relationships among the serialized classes registered by that DLL: all serialized classes are derived from one abstract base. While unloading the library, its void_caster singletons are destroyed but there are no shortcuts to remove from the global registrar since there are no parent-child relationships. All entries corresponding to those are still in the global registrar and POINT TO THE void_caster SINGLETONS ALREADY DESTROYED AND DISCARDED. When the main process exits, the registrar traversal repeats for whatever process-bound void_caster singletons are about to be destroyed. During these subsequent traversals, void_caster::recursive_unregister() visits the entries left after the previous explicit dll download and tries to identify the parent-child relationship. In doing so, it accesses the dangling vc pointers generating access violations: void_cast.cpp(Line 286): const void_caster * vc = *it; void_cast.cpp(Line 287): if(vc->m_parent == this){ //<--------------------- here is the access violation I can reproduce the crash systematically, but I am not sure about the reason or whether a simple unregistration is enough. I believe this is (again) a question for Robert, but I thank for any feedback I might get. Bogdan

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Help with shared_ptr and template
by Mario Chacon 10 Sep '10

10 Sep '10

Hello: I have this problem and I do not how to fix it, I know I cannot write template typedefs, its a limitiation of the C++ syntax, right? or I'm wrong? I saw that the best way is to wrap your typedefs in a struct, which can be templated, but I'm still stack with problems. The best way to explain it's with an example: #include <cstdlib> #include <iostream> #include <boost/shared_ptr.hpp> template< typename tvalue > class CValue { public: CValue( tvalue value ) : value_(value) {}; private: tvalue value_; }; template< typename tvalue > struct Type{ typedef boost::shared_ptr< CValue< tvalue > > pValue; }; int main(int argc, char *argv[]) { Type<bool>::pValue a; return EXIT_SUCCESS; } How can I create a shared_ptr for the template class "CVALUE"?? Please I do not know what else I can prove... :( Thank you.. Mario.. Salu2...

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[array] range check (at compile time)
by alfC 23 Jun '10

23 Jun '10

Hi, Lately I find myself using boost::array intesively, specially in small demo programs. Sometimes, when "manually" accessing the elements I type a index out of range. The library can detect these errors once the program is running but I found this a waste, also I was surprised not to see this kind of static check not implemented in the library. So I wanted to see if I could enforce range checking at compile time, and I come out with this solution. namespace boost{ //sorry about the namespace name template<size_t IDX, typename T, size_t N> const T& get(boost::array<T, N> const& arr){ BOOST_STATIC_ASSERT(IDX<N); return arr[IDX]; } template<size_t IDX, typename T, size_t N> T& get(boost::array<T, N>& arr){ BOOST_STATIC_ASSERT(IDX<N); return arr[IDX]; } } #include<iostream> void main(){ boost::array<double, 3> a = {1,2,3}; std::clog<<boost::get<2>(a)<<std::endl; // ok, (namespace specification needed, why?) std::clog<<boost::get<5>(a)<<std::endl; //does not compile return 0; } (I though about using enable_if instead of BOOST_STATIC_ASSERT but that would be too much overengineering.) Is this implemented already in some other way? Alfredo

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[GIL] Some questions about 2D iteration
by Brett Gmoser 08 Jun '10

08 Jun '10

Hello everybody, I've been toying with GIL a bit for the last few days in my spare time, and I've got a few questions that I can't seem to find answers to in the documentation. The following function which I've written works, but I'd like to get a better understanding of how to use iterators to accomplish the same task (the documentation says that view(x, y) = z is inefficient), as well as a few other things. The job of this function is to crop an image, discarding any white background. In other words, find the top-most, left-most, right-most, and bottom-most pixel that isn't the background color (white), and crop the image around those coordinates. template <typename ViewType, typename ImageType> void crop_image(ViewType& src, boost::scoped_ptr<ImageType>& dst) const { int top = 0; int right = 0; int bottom = 0; int left = 0; // Find the top, right, bottom, and left extents. First, find the top. for(int y=0; y < src.height(); ++y) { for(typename ViewType::x_iterator xpos = src.row_begin(y); xpos != src.row_end(y); ++xpos) { if(rgb8_pixel_t(255,255,255) != *xpos) { top = y; break; } } if(top) break; } // ... Do similar things for finding the right, bottom, and left extents. // We should now have the rectangle of the image, and it should be easy to copy everything over. dst.reset(new ImageType(1 + (right - left), 1 + (bottom - top))); for(int x = left; x <= right; ++x) for(int y = top; y <= bottom; ++y) view(*dst)((x - left), (y - top)) = src(x, y); } So, my first question is - is there a better way to do that first chore of finding each extent? Such as a way to use std::find or std::find_if, keeping in mind that I have to do two of the four sides in reverse (bottom-to-top to find bottom-most, right-to-left to find right-most)? The next question is about the final loop which copies from the source view to the newly created destination image. It seems that using iterators, I could do something like this, assuming that I had the above loops find iterator positions for all four extents (left, top, bottom, and right are iterators): // Start the copying process by creating a column iterator for the destination table beginning at column 0. // The top iterator starts at the top-most extent - and we cycle through the source image in a top-to-bottom, // left-to-right fashion. for(typename ImageType::view_t::y_iterator dst_y = view(*dst).col_begin(0); top <= bottom; ++dst_y,++top) { // The left iterator needs to be initialized with whatever row we're on - this appears to be impossible. There doesn't // seem to be any suitable way to do this, so consider it pseudocode. typename ViewType::x_iterator src_x = left.y(); // The destination X iterator also needs to know what Y position to begin on. You'd think you would be able to initialize // it with an iterator position, but it doesn't seem that you can. Again, this doesn't actually compile (it's the // view(*dst).row_begin(y) part). for(typename ImageType::view_t::x_iterator dst_x = view(*dst).row_begin(y); // Here, I need to be able to tell if src_x has hit the right extent. src_x <= right doesn't seem it will work, because // again right doesn't know it's Y position. src_x != right; // And increment both src and destination iterators. ++src_x,++dst_x ) { // Finally do the should-be-simple task of assigning the source pixel to the destination pixel. *dst_x = *src_x; } } If you read the comments, most of this doesn't seem to be possible. I've seen that there is a "transform_pixel_positions" algorithm that may do something close to what I want, but unfortunately I cannot find any documentation on it (other than mentioning that it exists, and a short example that really doesn't help - one of the few examples actually provided by the documentation). It seems to pass a unary argument to a functor, but that doesn't seem useful if I don't have both the X and Y coordinates, or an X iterator and Y iterator. Also, nowhere can I find where it says what the argument passed to the functor actually /is/. So after I figure these few things out, I'm hoping to be able to speed up my program a little bit. Right now everything is pretty slow using that view(x, y) method. I'd appreciate any help that anybody can give, thanks! Brett

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[statistics] chi-square test with boost
by Christine SINOQUET 31 May '10

31 May '10

Hello, I have to implement chi square tests. As I already use the boost library boost_1_38 for other purposes, I would like to use it for this purpose too. However I can find no documentation relative to this or the information I find is not correct. Can somebody indicate me how I can to use accumulators/statistics ? Is the boost_1_38 appropriate ? Which file should I include and which function should I use ? I just need to specify the columns in a matrix I wish to test for independence, the data itself and a threshold alpha. I would like the test statistic in return, as well as the p-value. If my question is not the object of this diffusion list, please tell me. Thank you in advance. Regards.

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Regression testing of boost libraries
by Yogesh Arora 10 May '10

10 May '10

Hi I am compiling boost 1.39.0 libraires on sun os. I have just started with using boost libraries and dont have much know about them. I read somewhere that after compilation i can run some regression tests to check if everything has compiled properly or not. When i looked at boost regression test webpage it mentioned that it would download the latest boost code and run the test case on it. However i dont want that, I have a copy of boost 1.39.0 which i have compiled on which i want to run these regression test cases. Is there a way to do that. Also someone mentioned that boost maintains a page on which i can check the status of boost unit test on different platforms, but i could not seem to find it. Can someone provide reference to that page. I am especially interested in status of boost libraires on Sun os with toolset=sun Thanks Yogesh

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[boost.test] 0 return code with expected failures?
by Ahmed Badran 16 Apr '10

16 Apr '10

Hi, I have a binary that runs unit tests, 3 tests fail and these tests I have marked as being expected failures after analysis. The binary however produces a non-zero exit code even with these tests marked as expected failures . Is there a way to have the binary return a zero exit code when all the failures are expected and non-zero when some other non-expected failure happens? The test setup uses automatic test registration. Regards, Ahmed

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[date_time] howto determine date format?
by Markus Werle 16 Apr '10

16 Apr '10

Hi! With the code below I try to automagically determine the date format found in input files. I'd expect the code below to find the date format "%d.%m.%Y" for "05.02.2008", but I got surprised by obtaining "%m/%d/%Y". A major pain it is with those dates. Whether my shallow knowledge of locales and imbue or boost::date_time (from boost-1.37.0) is to be blamed is beyond my horizon. I feel like date accepts '.' where I said "expect '/'", so I think this should be changed. I may be wrong. Could you please shed some light on the issue? Thanks, Markus #include <boost/assign/list_of.hpp> #include <boost/date_time/posix_time/posix_time.hpp> #include <boost/date_time/gregorian/gregorian.hpp> #include <boost/date_time/local_time/local_time.hpp> #include <boost/foreach.hpp> #include <boost/algorithm/string.hpp> #include <string> #include <list> inline std::string determine_date_format(std::string const & s) { using namespace boost::assign; using namespace boost::gregorian; std::list<std::string> possible_formats = // TODO: add others here! list_of ("%Y-%m-%d")("%Y/%m/%d")("%m/%d/%Y")("%d.%m.%Y"); bool inform_user = false; BOOST_FOREACH(std::string const & format, possible_formats) { if (inform_user) { std::cout << "Trying format '" << format << "' ..." << std::endl; } try { date_input_facet * input_facet = new date_input_facet(format.c_str()); std::istringstream iss(s); iss.imbue(std::locale(iss.getloc(), input_facet)); date d(not_a_date_time); iss >> d; if (!iss.fail() && (!d.is_not_a_date())) { return format; } std::cout << "WARNING: date format '" << format << "' does not match '" << s << "'." << std::endl; inform_user = true; } catch(...) { } } std::cout << "WARNING: date format not recognized. " << "Please reconfigure your measurement equipment " << "to ISO standard output!" << std::endl; return ""; } int main() { std::string the_date = "05.02.2008"; std::string format = determine_date_format(the_date); std::cout << the_date << " has date-time-format " << format << std::endl; return 0; }

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Visual Studio 2009 and BOOST_NO_MEMBER_TEMPLATE_FRIENDS
by Daniel Bradburn 06 Apr '10

06 Apr '10

I have just upgraded a project from Visual Studio 2005 to 2008 and suddenly I am getting compile errors using boost::multi_index: error C2247: 'boost::multi_index::detail::random_access_index<SuperMeta,TagList>::operator []' not accessible because 'boost::multi_index::detail::ordered_index<KeyFromValue,Compare,SuperMeta,TagList,Category>' uses 'protected' to inherit from 'boost::multi_index::detail::random_access_index<SuperMeta,TagList>' I figure that this is to do with the BOOST_MULTI_INDEX_PROTECTED_IF_MEMBER_TEMPLATE_FRIENDS define, so I tried changing #if _MSC_VER <= 1400 // 1400 == VC++ 8.0 # define BOOST_NO_MEMBER_TEMPLATE_FRIENDS #endif to #if _MSC_VER <= 1500 // 1500 == VC++ 9.0 # define BOOST_NO_MEMBER_TEMPLATE_FRIENDS #endif in visualc.hpp which fixes the compile error. Is this a bug with the visualc.hpp config in boost? I can't believe I would be the first to spot it. Has anyone else experienced this? Are member template friends actually supported in visual c++ 9? _________________________________________________________________ Download gratis emoticons voor Messenger http://www.rulive.nl/aspx/emoticons.aspx

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[boost.asio] error Software caused connection abort
by imin imup 06 Apr '10

06 Apr '10

Hello, When I use a tcp socket to connect to remote host, I may get an "actively refused" or "time out" error in 1st time. That's normal. Then when I retry to connect to remote host, I "always" got "Software caused connection abort" error for every rtrial. It seems a programming issue. Could anyone explain what this error mean and how to avoid it? or point me to some document? Thanks Imin

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