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Re: [Boost-users] [iterators] NULL pointer initialization and comparison using iterator_facade
by Lang Stefan 23 Apr '08

23 Apr '08

> On Tue, Apr 22, 2008 at 10:43 AM, Lang Stefan > <SLang(a)starragheckert.com> wrote: > > I have a big problem though: The project I am working on > is quite big > > and I intend to replace a particular typedef (currently > simply a pointer > > to a struct) with this iterator class. There are two kinds of > > instructions though that my iterator class currently can't > cope with: > > > > 1. Initializing a 'pointer' with NULL (in other words, I need a > > constructor with one argument of type int, but only in case that > > argument's value is 0) > > > > How about some really weird pointer type? If you did a member > function type that doesn't actually exist, you should be able to > construct with NULL, but nothing else. > Whatever you have in mind, I have no idea what you mean. Could you elaborate please? Btw., I did consider somehow introducing one of the boost smart pointer types to resolve this issue, but apparently even the smart pointers cannot directly deal with NULL values (e.g. comparison to NULL requires calling the get() method first). I could of course introduce special functions for semantically equal purposes, but that would force me to change several thousand lines of code to match the new syntax. I can think of better ways to waste my time... Is it possible to construct metafunctions that allow a function argument of NULL, but not any other integer value? Or at least cause the compiler to call out whenever a non-NULL argument is provided? Cheers, Stefan

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[iostreams]combining serialization archive with iostreams filtering_streambuf
by cpper 23 Apr '08

23 Apr '08

Hi all: I have spent a day long in finding a way of combining serialization archive with iostreams filtering_streambuf but now I encounter a strange problem, here is my code: #include <sstream> #include <boost/iostreams/device/back_inserter.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/copy.hpp> #include <boost/iostreams/filter/bzip2.hpp> #include <boost/archive/binary_oarchive.hpp> #include <boost/archive/binary_iarchive.hpp> #include <boost/serialization/string.hpp> #include <boost/iostreams/stream.hpp> #include <vector> int main () { std::vector<char> store; boost::iostreams::filtering_ostreambuf out; out.push(boost::iostreams::bzip2_compressor()); out.push(boost::iostreams::back_inserter(store)); { boost::archive::binary_oarchive oa(out); oa << "abc"; // archive closed when destructors are called //out.pop ();//call before oa destroyed, crashed!!!! } out.pop ();//call after oa destroyed the behavior seems normal //out.reset (); boost::iostreams::filtering_istreambuf in; in.push(boost::iostreams::bzip2_decompressor()); in.push(boost::make_iterator_range(store)); { std::string aft; boost::archive::binary_iarchive ia(in); ia >> aft; } } if I call pop() or reset() before archive destructor called. exception in: C:\Program Files\Microsoft Visual Studio 9.0\VC\crt\src\streambuf in this member method of std::streambuf int pubsync() error message is below: Unhandled exception at 0x10499231 (msvcp90d.dll) in basic_usage.exe: 0xC0000005: Access violation reading location 0xfeeeff1e. If I call out.pop() after oa destroyed,the behavior is exactly what I want. But I just wonder why it goes in this way? Code like below { boost::archive::binary_oarchive oa(out); oa << "abc"; } out.pop ();//call after oa destroyed the behavior seems normal which appears that I have done something wrong... I'm using VS2008TS under Win2003SP2 Can anybody help?

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[serialization]
by Robert Bielik 23 Apr '08

23 Apr '08

I'm going to serialize my objects via the binary archives, since there seems to be some issues with the wide variants, I'd like to know what happens to wide strings serialized? Are they just copied verbatim, as wide char data that is? TIA /R

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Boost::interprocess, managed_mapped_file not working properly on Mac
by Martin_Thomas＠McAfee.com 22 Apr '08

22 Apr '08

I was trying to make a small program that uses Multi-Index and Interprocess work on a Mac and was convinced that I was doing something wrong until I tried the simple example in the Multi-Index docs and found it also fails to work on Mac but works on Linux. The example is here: http://www.boost.org/doc/libs/1_35_0/libs/multi_index/example/ip_allocat or.cpp and the problem is that boost::interprocess::open_or_create does not work -it only creates. I built the example, add a few books and then quit. When I restarted the app on Linux, it listed the books from the previous run but the Mac version did not manage to do the same. Running on Linux Redhat FC8 and Mac OSX 10.5 Cheers // Martin

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[extension] conflict with boost::optional
by David Matz 22 Apr '08

22 Apr '08

Hello, I have some trouble using boost::extension and boost::optional together in a project (MSVC 7.1). The compiler complains that boost::get is not an element of extensions::shared_library. Without the optional.hpp header everything works fine. It seems the for some reason the macro BOOST_EXTENSION_SHARED_LIBRARY_GET_FUNCTION isn't valid when shared_library.get<>() is called but I can't find out why. A small code snippet that reproduces the error file: test_extension_and_optional.cpp #include <boost/optional/optional.hpp> // included for some reason #include <boost/extension/shared_library.hpp> #include <boost/extension/convenience.hpp> // load_single_library void loadExtension () { boost::extensions::factory_map fm; // we don't need the following line to produce the compiler error //boost::extensions::load_single_library(fm, ".", "external_function_name"); } error: error C2039: 'boost::get': Ist kein Element von 'boost::extensions::shared_library' Thanks in advance. David -- David Matz ---------------------------- Software Developer Spatial View GmbH mail: david.matz(a)spatialview.com phone: +49 351 - 4 50 33 44 registration court: Amtsgericht Dresden, HRB 21104 managing directors: Wolfgang Opel, Jens Wiegrebe

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[python] Expose memory-aligned data types?
by Dan Fike 22 Apr '08

22 Apr '08

Using Boost.Python, is it possible to expose a C++ memory-aligned data type to Python? For example, I want to expose this data type. class __declspec(align(16)) foo { public: foo() {}; bool isAligned() { if ((int)this % 16 == 0) { return true; } else { return false; } } private: int a, b, c, d; }; I've written the following code to expose this class to Python: BOOST_PYTHON_MODULE(myModule) { boost::python::class_<foo>("foo", boost::python::init<>()) .def("isAligned", &bar.isAligned) ; } When compiling this code (MSVC 8.0, VS2005, Win32), I get the following error (entire error listed at the bottom): d:\...\boost\python\converter\as_to_python_function.hpp(21) : error C2719: 'unnamed-parameter': formal parameter with __declspec(align('16')) won't be aligned Note that I used to get a STATIC_ASSERTION_FAILURE in the type_with_alignment class definition when compiling with Boost 1.34. I found adding a 16-byte aligned struct type to the BOOST_TT_ALIGNMENT_BASE_TYPES list in type_with_alignment.hpp made the ASSERT go away, but introduced the above error. In an attempt to fix it, I downloaded Boost revision 43984 from early April, 2008, which included a patch that I thought would help me. See http://svn.boost.org/trac/boost/changeset/43984. While the type_with_alignment.hpp included in that revision did correct the STATIC_ASSERTION_FAILURE, I am still hitting the above error. Now, if I try to build the same code in x64 instead of Win32 (again, from revision 43984), I do not encounter the error. Not only does it compile, but I have verified that any objects 16-byte aligned objects I instanciate in Python are actually aligned correctly. Unsurprisingly, however, the x64 build produces the same error when I try to expose a 32-byte aligned data type. On the other hand, the Win32 build still complains if I try it with an 8-byte aligned data type. I'm hoping there is a piece of Boost.Python code missing from the class exposition that I don't know about. I've scoured the documentation and internet (and code) for such a thing, but I may have overlooked it. Any advice? -Dan Fike Here is the entire error, as printed by VS2005... d:\...\boost\python\converter\as_to_python_function.hpp(21) : error C2719: 'unnamed-parameter': formal parameter with __declspec(align('16')) won't be aligned d:\...\boost\python\to_python_converter.hpp(88) : see reference to class template instantiation 'boost::python::converter::as_to_python_function' being compiled with [ T=foo, ToPython=boost::python::objects::class_cref_wrapper>> ] d:\...\boost\python\to_python_converter.hpp(82) : while compiling class template member function 'boost::python::to_python_converter::to_python_converter(void)' with [ T=foo, Conversion=boost::python::objects::class_cref_wrapper>>, has_get_pytype=true ] d:\...\boost\python\object\class_wrapper.hpp(26) : see reference to class template instantiation 'boost::python::to_python_converter' being compiled with [ T=foo, Conversion=boost::python::objects::class_cref_wrapper>>, has_get_pytype=true ] d:\...\boost\python\object\class_metadata.hpp(272) : see reference to class template instantiation 'boost::python::objects::class_cref_wrapper' being compiled with [ Src=foo, MakeInstance=boost::python::objects::make_instance> ] d:\...\boost\python\object\class_metadata.hpp(229) : see reference to function template instantiation 'void boost::python::objects::class_metadata::maybe_register_class_to_python(T2 *,boost::mpl::false_)' being compiled with [ T=foo, X1=boost::python::detail::not_specified, X2=boost::python::detail::not_specified, X3=boost::python::detail::not_specified, T2=foo ] d:\...\boost\python\object\class_metadata.hpp(219) : see reference to function template instantiation 'void boost::python::objects::class_metadata::register_aux2>(T2 *,Callback)' being compiled with [ T=foo, X1=boost::python::detail::not_specified, X2=boost::python::detail::not_specified, X3=boost::python::detail::not_specified, T2=foo, Callback=boost::integral_constant ] d:\...\boost\python\object\class_metadata.hpp(217) : while compiling class template member function 'void boost::python::objects::class_metadata::register_aux(void *)' with [ T=foo, X1=boost::python::detail::not_specified, X2=boost::python::detail::not_specified, X3=boost::python::detail::not_specified ] d:\...\boost\python\class.hpp(174) : see reference to class template instantiation 'boost::python::objects::class_metadata' being compiled with [ T=foo, X1=boost::python::detail::not_specified, X2=boost::python::detail::not_specified, X3=boost::python::detail::not_specified ] d:\...\boost\python\class.hpp(205) : see reference to class template instantiation 'boost::python::class_::id_vector' being compiled with [ W=foo ] d:\...\MyProject\my_project_python_modules.h(77) : see reference to function template instantiation 'boost::python::class_::class_>(const char *,const boost::python::init_base &)' being compiled with [ W=foo, DerivedT=boost::python::init<> ]

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[iterators] NULL pointer initialization and comparison using iterator_facade
by Lang Stefan 22 Apr '08

22 Apr '08

Hello list, I have created a generic iterator template class for arrays that also doubles as container-wrapper for the array in question. To achieve this I have based my class on boost::iterator_facade . I have defined all the neccessary functions as described in the documentation and mostly the iterators work as intended. Here's a cut-down version: #include <boost/type_traits/is_convertible.hpp> #include <boost/utility/enable_if.hpp> #include <boost/iterator/iterator_facade.hpp> template<class Value> class cArrayIterator : public boost::iterator_facade< cArrayIterator<Value> , Value , boost::random_access_traversal_tag > { private: struct enabler {}; public: cArrayIterator() : first(0),size(0),position(0) {} cArrayIterator(Value* _first, difference_type _size, difference_type _position = 0) : first(_first),size(_size),position(_position) {} template<class OtherValue> cArrayIterator( const cArrayIterator<OtherValue>& other , typename boost::enable_if< boost::is_convertible<OtherValue*,Value*> , enabler >::type = enabler() ) : first(other.first),size(other.size),position(other.position) {} private: Value* first; difference_type position; difference_type size; friend class boost::iterator_core_access; void advance(difference_type n){ position += n; } void decrement(){ --position; } Value& dereference() const{ return first[position]; } template<class OtherValue> difference_type distance_to(const cArrayIterator<OtherValue>& z) const{ return z.position - this->position; } template<class OtherValue> bool equal(const cArrayIterator<OtherValue>& other) const{ return this->first + this->position == other.first + other.position; } void increment(){ ++position; } }; I have a big problem though: The project I am working on is quite big and I intend to replace a particular typedef (currently simply a pointer to a struct) with this iterator class. There are two kinds of instructions though that my iterator class currently can't cope with: 1. Initializing a 'pointer' with NULL (in other words, I need a constructor with one argument of type int, but only in case that argument's value is 0) 2. Comparing a 'pointer' to NULL (again, comparison to int argument, but only makes sense for the value 0) I did add a constructor with only one argument (of type pointer to the underlying object's type) and could eliminate problem 1. However I feel it's not quite right, since for my array iterator it doesn't make any sense to initialize it with just one pointer and no further information (it requires pointer to first element, position, and size of array), so in cases where the pointer argument is not NULL this constructor shouldn't even be available! Here's the code for the new constructor: cArrayIterator(Value* _first) // workaround : first(_first),position(0) { if (NULL == _first) size = 0; else size = 1; // not really sensible, but the best I can think of atm } Moreover, I hoped this constructor would also eliminate problem 2 by implicitely converting the int value of 0 to a NULL iterator, but it didn't. I tried to provide my own comparison operators, but so far failed to meet the syntax the compiler would recognize as a fit for a comparison int to iterator. This is what I got so far: template <class Value> bool operator==(cArrayIterator<const Value> const left, cArrayIterator<Value> const right) { return false;// I'll take care of that once the function gets actually called :/ } How do I correctly define a comparison operator that compares a 'NULL pointer' to a class representing a pointer? Or does iterator_facade already provide a way to deal with this? Stefan

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[thread] how to use thread::timed_join
by Johan Råde 22 Apr '08

22 Apr '08

I want to do a timed join, with a relative time of 0.1s. I can not figure out from the docs how to do this. I find the prototypes somewhat mystifying: bool timed_join(const system_time& wait_until); template<typename TimeDuration> bool timed_join(TimeDuration const& rel_time); What is system_time? What should TimeDuration be? I'm using Windows. Thank you, Johan Råde

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Edges list
by Chartier Nicolas 22 Apr '08

22 Apr '08

I'd like to know how I could retrieve a weighted edges list from a graph, without forgetting vertices and weight, in a list for example. Any suggestion welcome ;) NC ------- Chartier Nicolas +33 (0)6 78 32 94 33

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Re: [Boost-users] Mingw cross compilation
by James Choa 22 Apr '08

22 Apr '08

> Hi James, > > I managed to cross-compile static release builds of serialization, > filesystem, system, date_time, and program_options from boost 1.35.0 > with i386-mingw32 gcc 4.3.0 (http://mingw-cross.sourceforge.net/) under > Fedora 8 using a three-step procedure: > - create a user-config.jam file with content: > using gcc : : i386-mingw32-gcc : ; > - run bjam (assuming you have compiled it already): > bjam --user-config=user-config.jam --toolset=gcc link=static release ... > - manually run i386-mingw32-ranlib on the generated libraries > > There might be a better way to do this, but at least the above worked > for me. > /Mikko Thanks! I'll give it a try

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