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

[Program Options] Positional args in help message
by Lindley M French 10 Nov '10

10 Nov '10

The examples for how to use positional arguments are great and seem to work fine. However, I'm wondering if there's an automatic way to include that information in the help message. In particular, since the tutorial goes to the trouble of telling you how to exclude the positional options from the options help, it would be nice to know what to replace it with. I could manually write a line detailing the usage before outputting the options description, of course, but I was wondering if there was anything in PO to handle this automatically.

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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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[Chrono] How to report problems?
by Roland Bock 28 May '10

28 May '10

Hi, after having received a push in the right direction by Howard yesterday, everything works fine so far, except for for the following two details: a) I get some warnings about unused parameters when using the stopclock. For instance: include/boost/chrono/stopwatch_reporter.hpp:81: warning: unused parameter ‘ec’ The fixes are trivial in all cases I encountered. b) The thread_clock part of the tutorial looks pretty broken. Not sure if more things will come up, but if so, where should I send them? Maybe this information would be a nice addition to the FAQ until chrono makes it into boost? Thanks for this cool library! Regards, Roland

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boost::thread - many compiler warnings
by Manfred Schwind 12 May '10

12 May '10

Hi, we are using boost to develp cross-platform stuff. I am the Mac developer. The Mac is a 64 bit Intel machine, development environment is Xcode, of course, using gcc as compiler. To create code as robust as possible I always turn on as many warning levels as possible. Usually I am using this: -Wall -Wextra -Wconversion -Wshorten-64-to-32 This worked great with all basic boost stuff that we've used previously. Now I tried just to include thread.hpp and I get many many compiler warnings! I just do: #include "boost/thread.hpp" The warnings are just two kinds of warnings: 1.) warning: implicit conversion shortens 64-bit value into a 32-bit value 2.) warning: missing initializer for member '...' An example for the first warning can be found in gregorian_calender.ipp (just showing relevant parts): template<typename ymd_type_, typename date_int_type_> BOOST_DATE_TIME_INLINE int gregorian_calendar_base<ymd_type_,date_int_type_>::week_number(const ymd_type& ymd) { ... unsigned long week = (juliantoday + day - julianbegin + 4)/7; if ((week >= 1) && (week <= 52)) { return week; } ... Here's clearly missing a cast to tell the compiler that it's ok to return the unisigned long as int. On most 64 bit systems, long is 64 bit but int is 32 bit. The second warning is caused by the following line in conversion.hpp: std::tm datetm = {}; // zero initialization is needed for extension members, like tm_zone In this line I get the "missing initializer" warning for every member of the struct, e.g. tm::tm_sec, tm::tm_min, tm::tm_hour etc. What's the intension by initializing with empty braces? IMO this is not a standard initialization method. Is there any chance that these errors get fixed? Any ideas how to use thread.hpp without reducing my warning levels? Does anyone have the same problems? Regards, Manfred Schwind -- http://mani.de - friendly software iVolume - listen to music hands-free LittleSecrets - the encrypted notepad Sahara - sand in your pocket Watchdog - baffle the curious

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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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Serialization of a complex data structure
by Marco Meoni - Sbaush 10 May '10

10 May '10

Hi all. I've to serialize a structure that has as attributes two structures. An example is: struct Example{ Container* results_container; MyMap this_is_a_map; Example(){} ... ... }; where Container* is a pointer to another struct, defined by me, and MyMap is a c++ map. I've tried to serialize it using the shared_ptr example of boost serialization: struct Example{ friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int /* file_version */){ } Container* results_container; MyMap this_is_a_map; Example(){} ... ... }; and in the main i call: boost::shared_ptr<Example> myExample(new Example); ... ... // serialize it { std::ofstream ofs(filename.c_str()); boost::archive::text_oarchive oa(ofs); oa << myExample; } boost::shared_ptr<Example> myNewExample(new Example); { // open the archive std::ifstream ifs(filename.c_str()); boost::archive::text_iarchive ia(ifs); // restore the schedule from the archive ia >> myNewExample; } Now myNewExample is a well format instance of Example, but the attributes are empty. Can anyone help me? I would not have to change all files with nested structures, as are many, not just two as in the example Thanks all. Marco. -- Marco Meoni - Sbaush www.marcomeoni.net

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