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A linking error on using lambda expression in dll . Can anyone with kindness help me?
by fmingu 23 Jul '09

23 Jul '09

I am using Dev-C++ and lambda expression (boost 1.34.1). I created a dll containing a class. And want other programs to use the memberfunctions in the class. the dll.h is: .......................... #if BUILDING_DLL # define DLLIMPORT __declspec (dllexport) #else /* Not BUILDING_DLL */ # define DLLIMPORT __declspec (dllimport) #endif /* Not BUILDING_DLL */ ............ class DLLIMPORT classA{ private: ............ public: int function1(const int& ); ............... }; the dll.cpp is: # include "dll.h" ....................... int classA::function1(const int& testnumber){ ..................... } ........................ In the classA::function1 in dll.cpp I used the lambda expression and the above dll is created OK. and the main executable using the dll is: # include "dll.h" ................................ int WINAPI WinMain (HINSTANCE hThisInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int nFunsterStil) ....................... classA instanceA; instanceA.function1(3); ..................... the complier told me no errors but the linker told me that : [Linker error] undefined reference to `classA::Function1(int const&)' And I do not know how to solve it. Does this error occur due to the use of lambda expression? Can anyone with kindness help me?

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Re: [Boost-users] strange serialization compilation issue - serialize function not being compiled
by G, Benjamin (NSN - IN/Bangalore) 23 Jul '09

23 Jul '09

I forgot to mention, I am using boost 1.33.1 and compiling on windriver (x86) linux. ________________________________ From: G, Benjamin (NSN - IN/Bangalore) Sent: 23 July, 2009 1:24 PM To: 'boost-users(a)lists.boost.org' Subject: strange serialization compilation issue - serialize function not being compiled Hi, I have a class which has got the serialize function implemented. template<class Archive>void myClassB::serialize( Archive& ar, const unsigned int) Somehow, this function is skipped and doesn't appear even in the object file created for this file which gives me undefined reference errors later when linking. I have included : #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/archive/binary_oarchive.hpp> #include <boost/archive/binary_iarchive.hpp> In my cpp file. Does this sound faimiliar to anyone? Or am I going wrong somewhere? Thanks in advance - Benjamin Jacob.

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multiple levels of bind nesting
by Zachary Turner 23 Jul '09

23 Jul '09

I have some code that implements an asynchronous worker model where a client calls some function to request an asynchronous operation and passes a callback function, whose type is determined by a template parameter. e.g. class worker { template<class Handler> void async_do_work(Handler h) { ... } }; class client { void start_work(); void work_finished(boost::system::error_code ec, size_t bytes_transferred); }; However there are many classes implementing async_do_work but which do the work in a different way. For this I use a boost::variant<A&, B&, ...> for each type and use a boost::static_visitor to delegate to the appropriate async_do_work method. This uses code such as the following: void client::start_work() { apply_visitor( bind(do_work_visitor(), _1, protect(bind(&client::work_finished, this, _1, _2))) , work_variant_); } So from async_do_work's point of view, it receives a function with 2 arguments. How async_do_work operates internally should be separated from the client. It may not even use another thread, or it may combine the efforts of multiple threads to achieve the result. So because of that, I want async_do_work to intercept the callback before it gets posted back to the original caller. To do this, I tried the following in the implementation of worker: class worker { public: template<class Handler> void async_do_work(Handler h) { //impl supports the same basic interface as worker impl->async_do_work( bind(&worker::intercept_handler<Handler>, this, h, _1, _2)); } private: template<class Handler> void intercept_handler(Handler real_handler, boost::system::error_code ec, size_t bytes_transferred) { //do whatever is necessary and then call the real handler. real_handler(ec, bytes_transferred); } }; However this doesn't work. I've also tried protect(bind in the async_do_work function and that doesn't work either. Is it supposed to be possible to nest binds arbitrarily deep or is this just a limitation? Or am I just doing it wrong? Regards

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[program_options] positional options starting with a '-' sign
by Ian McCulloch 23 Jul '09

23 Jul '09

Hi, I have an app using program_options, which has various optional arguments, followed by any number of floating point numbers, which are read as positional options. A user just pointed out that it fails with an 'unknown option -0' error if any of those positional options are negative, because it tries to interpret a number like "-0.34" as an option. Is there a way to treat unregistered options as positional arguments? allow_unregistered() doesn't quite do it - it doesn't give an error anymore but neither does it treat "-0.34" as a positional option (even if it is not the first positional argument). Regards, Ian McCulloch

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[iostreams] gzip filter produces files with trailing garbage
by Michael Harris 23 Jul '09

23 Jul '09

Hi, I am using boost::iostreams in a project that I am currently working on. The relevant part of my code is shown below: #include <boost/iostreams/device/file_descriptor.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/filter/gzip.hpp> ... void FileDataStore::write(DataSet *ds) { filtering_ostream os; // Check if we are writing a gzipped file int iext = this->filename.find_last_of('.'); if (iext != std::string::npos && this->filename.substr(iext+1) == "gz") { os.push(gzip_compressor()); } try { os.push(file_descriptor_sink(this->filename)); } catch (std::ios_base::failure e) { throw IOException() << errmsg_info((boost::format("Error opening file '%s': %s") % this->filename % strerror(errno)).str().c_str()); } // Write my stuff to os os.flush(); os.pop(); } Basically, if the filename being used ends in .gz I want the file written through a gzip filter so it is stored gzipped. The problem is: if I unzip the resulting file using gzip I get a message like this: gzip: myfile.gz: decompression OK, trailing garbage ignored The file content is OK but this message is annoying. What am I doing wrong that causes this? Many thanks, Regards // Mike

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[multi_array] Assertion when resizing empty array
by John Reid 22 Jul '09

22 Jul '09

Resizing an empty array no longer seems to work. My code worked fine with boost 1.38, now it causes an assertion with the latest boost trunk from svn. The code is: #include <boost/multi_array.hpp> int main( int argc, char * argv[] ) { boost::multi_array< double, 2 > a; a.resize( boost::extents[2][3] ); return 0; } The assertion is: multi_array_resize: /home/john/Dev/ThirdParty/boost/boost-trunk/boost/multi_array/base.hpp:446: ArrayRef boost::detail::multi_array::multi_array_impl_base<T, NumDims>::generate_array_view(boost::type<Reference>, const boost::detail::multi_array::index_gen<NumDims, NDims>&, const typename boost::detail::multi_array::associated_types<T, mpl_::size_t<NumDims> >::size_type*, const typename boost::detail::multi_array::associated_types<T, mpl_::size_t<NumDims> >::index*, const typename boost::detail::multi_array::associated_types<T, mpl_::size_t<NumDims> >::index*, TPtr) const [with ArrayRef = boost::detail::multi_array::multi_array_view<double, 2ul>, int NDims = 2, TPtr = double*, T = double, long unsigned int NumDims = 2ul]: Assertion `index_bases[n] <= start && start < index_bases[n]+index(extents[n])' failed. Aborted My compiler is: john@john-dell:~/Dev/MyProjects/Bio/hmm$ gcc -v Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.3.3-5ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-mpfr --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4) I updated from svn today. I think the code creates a view on the old data in order to retain it. The assertion happens because this view is empty. Regards, John.

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Spirit qi recommendations ?
by Avi Bahra 22 Jul '09

22 Jul '09

In order to reduce compile times I have decided to rewrite the parser/grammar from classic to spirit qi (spirit 2.1). My understanding is that faster compiles come from easier modularisation available under spirit qi. (As shown in mini_c example, in the boost tree) However I need this to be portable to as many platforms as possible. In my case minimum set is Linux,HP-UX, AIX. So my fall-back is boost 1.38. So how much has boost spirit qi changed between 1.38 and present ? How are defects reported against spirit qi, integrated back to past releases, or is there any recommended patch type mechanism, that supports redistribution of my local boost tree. Or is simply better to use spirit independently from boost? Are there any issues/guidelines that people have found in transitioning from classic to Qi. In my case I made heavy use of closures. I have not seen closures in any of spirit qi examples, Assuming there is equivalent functionality to closures ? I would interested in any recommendations before starting on this project. Best regards, Ta, Avi

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weak_ptr and thread safety
by Pavel Shevaev 22 Jul '09

22 Jul '09

Guys, could you please clarify whether the following usage of weak_ptr is thread safe: //thread A: shared_ptr<Foo> p = wp.lock(); //thread B: p.reset(); I believe it's not thread safe as it looks very similar to the example 3 from the shared_ptr documentation: // thread A p = p3; // reads p3, writes p // thread B p3.reset(); // writes p3; undefined, simultaneous read/write Am I right in my assumption? And if yes, could you please give any recommendations for the following use case. I have a networking thread which owns a set of net session objects stored as shared_ptrs. I also have another thread where some entities have weak_ptrs members pointing to net session objects from networking thread. From time to time net sessions are erased and I think when at the very this moment entity object from another thread tries to lock() the net session and access it seg. fault happens. Thanks in advance. -- Best regards, Pavel

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Re: [Boost-users] [Fusion] Understanding Fusion
by Cromwell Enage 22 Jul '09

22 Jul '09

--- On Sat, 7/18/09, Robert Jones wrote: > Hi All > > I'm very much a Fusion newbie, just getting may head around it, so a > really basic question! > > From the intro page, when we write > > #include <boost/fusion/sequence.hpp> > #include <boost/fusion/include/sequence.hpp> > > vector<int, char, std::string> stuff > for_each(stuff, print_xml()); > > > am I correct in believing that there is no loop involved in the > for_each, and that this resolves, at compile time, to a linear > list of function calls? Yes. IIRC, it resolves to the equivalent of: print_xml()(int()); print_xml()(char()); print_xml()(std::string()); HTH, Cromwell D. Enage

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Creating a fixed size managed_mapped_file
by Eli Zakashansky 22 Jul '09

22 Jul '09

Hello, I would like to create a managed_mapped_file which should contain a certain number of elements[n] of a certain size [k], therefore the required size which I would like to use is n*k (size of element * number of elements). But when the file is created [new bip::managed_mapped_file (bip::create_only, fileName, n*k);] besides the elements which I would like to placed in this file, a segment manager<http://www.boost.org/doc/libs/1_39_0/doc/html/interprocess/architecture.htm…> is also placed there and occupies an uncertain space [http://www.boost.org/doc/libs/1_39_0/doc/html/interprocess/architecture.htm…] I would like to know how much memory (size of file) shall I require in the C-tor so that my file will have enough space for n elements of size k, and be as compact as possible. Thanks in advance, Eli.

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