March 2009 - Boost - lists.preview.boost.org

[asio] basic_datagram_socket::send_to
by Miroslav Beranič ml. 23 Mar '09

23 Mar '09

Greetings, will method basic_datagram_socket::send_to flush data immediately to the endpoint or will first fill its internal buffer and than flush data to endpoint? I would like to make sure, data gets flushed to endpoint when this method is called. Is there any other way to flush data to endpoint? Does any socket::set_option(option); makes difference to behaviour of send_to method ? Why isn't it possible to set buffer size lower than 1024 (low-level restriction?), with method (basic_datagram_socket::send_buffer_size()) There is no documentation about this. Best regards, ----- Miroslav Beranič ml.

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Request interest in Bloom filters
by vicente.botet 23 Mar '09

23 Mar '09

Hi, I need for my application bloom filters. Do you know of a good boostified generic implementation? Is there any interest in such a generic bloom filters library in Boost? Thanks, Vicente

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[ptr_container] ptr_map + abstract class = error
by Ross Levine 23 Mar '09

23 Mar '09

The following code does not compile in VS2008: #include <boost/ptr_container/ptr_map.hpp> class A { public: virtual void is() = 0; }; class B : public A { public: virtual void is() {} }; int main() { boost::ptr_map<int, A> c; int i = 1; c.insert(i, new B); A& my_ref = c[1]; // error: cannot instantiate abstract class } It seems that using operator[] creates a new A for an unmatched key, which creates an abstract instance. Using the find method works fine. Should this be documented? The example in the documentation uses operator[] on an ABC, and thus shouldn't compile either.

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Re: [boost] [gsoc][student] Proposal
by Kasra 23 Mar '09

23 Mar '09

Hi, > Why the C-like interface? > Why not work with iterator, or better, ranges? The reason for that is there are multiple layers of encapsulation in the library. block_cipher_type is the core algorithm, which is part of the lowest-level of the API. However, there is a block_cipher wrapper "block_cipher" that provides C++ semantics (iterators, ranges, specialised "crypto_buffers" and etc). With Best Regards --- Kasra Nassiri

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[soc2009] Project ideas: on the wiki, please
by troy d. straszheim 23 Mar '09

23 Mar '09

All, Google will allocate funded student positions as outlined here: http://socghop.appspot.com/document/show/program/google/gsoc2009/studentall… Meaning that it is in our interest to get as many student applications as possible. We don't know how many will be approved by google. Many students will peruse the gsoc google-hosted websites looking for project ideas, and the soc2009 wiki page will be linked to from there: https://svn.boost.org/trac/boost/wiki/soc2009 Please post your project ideas there, where interested students will be most likely to stumble on them. -t

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phoenix for_each and std::cout
by Sandeep Gupta 23 Mar '09

23 Mar '09

Hi, I am trying to use phoenix::for_each to print each element of iterator range. Would appreciate if any clarification as to why statements 1 and 2 are giving compile errors. Thanks sandeep //-------------code snippet int x; counting_iterator<int> first(0), last(10); iterator_range<counting_iterator<int> > ir(first, last); phoenix::for_each(ir, std::cout<<x<<' ')(); //stmt 1 ; compile error phoenix::for_each(ir, std::cout<<arg1<<' ')(); //stmt 2; compile error

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How to submit bjam patches?
by Steven Solie 22 Mar '09

22 Mar '09

How do I go about submitting patches for bjam? Thanks, --Steven

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Re: [boost] [Smart Ptr][Bind] Implementaion of Weak Callback Function
by Artyom 22 Mar '09

22 Mar '09

> weak_ptr< A > p; > > bind(&A::foo, throw_if_invalid(p)); > bind(&A::foo, ignore_if_invalid(p)); > bind(&A::foo, call_if_invalid(p, bar)); // bar I think this is little bit problematic, because proxy weak_ptr_caller should know the signature of A::foo to provide correct "R operator()(args...)" Maybe, additional policy for weak_fn would be better void A::foo(int); function<void(int)> bar; bind(weak_fn(&A::foo,p),_1); // default ignore bind(weak_fn(&A::foo,p,throw_on_invalid()),_1); bind(weak_fn(&A::foo,p,bar),_1); // call bar on invalid This would not require changes in bind and also weak_fn would be useful without bind as well. Like function<void(int)> foobar=weak_fn(&A::foo,p); It would be simple to update weak_fn to add policy Artyom

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[circular buffer] logic behind set_capacity vs rset_capacity?
by Ross Levine 22 Mar '09

22 Mar '09

I was using Boost.Circular_buffer for the first time today, and noticed that the set_capacity and rset_capacity methods did the opposite of what I expect; namely, set_capacity will clip elements from the back and rset_capacity from the front, despite the fact that insertion using push_back will overwrite elements from the front. Is there any rationale for this operation?

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puzzle for gcc gurus
by Robert Ramey 22 Mar '09

22 Mar '09

I'm trying use gdb under cygwin to debug one of the tests in the serialization library. I've done the before but only with static linking. This time, the failure only occurs when using the serialization library as a shared library. So I want to trap/trace inside the boost_serialization DLL. Using the cygwin bash shell, I get the following. $ set | grep LD LD_LIBRARY_PATH=C:/BoostRelease/bin.v2/libs/serialization/build/gcc-3.4.4/debug OLDPWD=/cygdrive/c/boostrelease Robert Ramey@rrsd01 /cygdrive/c/boostrelease/libs/serialization/test $ cat t.g file C:/BoostRelease/bin.v2/libs/serialization/test/test_diamond_text_archive.te st/gcc-3.4.4/debug/test_diamond_text_archive.exe sharedlibrary C:/BoostRelease/bin.v2/libs/serialization/build/gcc-3.4.4/debug/bo ost_serialization-gcc34-d-1_39.dll Robert Ramey@rrsd01 /cygdrive/c/boostrelease/libs/serialization/test $ gdb -x t.g GNU gdb 6.8.0.20080328-cvs (cygwin-special) Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "i686-pc-cygwin". (gdb) r Starting program: /cygdrive/c/BoostRelease/bin.v2/libs/serialization/test/test_d iamond_text_archive.test/gcc-3.4.4/debug/test_diamond_text_archive.exe [New thread 3952.0xb10] gdb: unknown target exception 0xc0000135 at 0x7c964ed1 Program exited with code 030000000465. You can't do that without a process to debug. (gdb) (gdb) l main 169 int test_main(int argc, char * argv[]); 170 171 #include <boost/serialization/singleton.hpp> 172 173 int 174 main(int argc, char * argv[]){ 175 176 boost::serialization::singleton_module::lock(); 177 178 BOOST_TRY{ (gdb) Things crash immediately. I believe that the exception 0xc0000135 at 0x7c964ed1 refers to the inability to load some required DLL. Note that I can list the source code of the mainline program so things do seem to get loaded. I realize that his might be off topic - but I'm sort of desparate. Any help appreciated. Robert Ramey

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[Smart Ptr][Bind] Implementaion of Weak Callback Function "weak_fn"
by Artyom 22 Mar '09

22 Mar '09

Hello, Today boost::bind allows to use shared_ptr to ensure that when the function is called the object exists: shared_ptr<bar> bar_ptr; function<void()> foo; foo=bind(&bar::slot,bar_ptr) Now even if we call bar_ptr.reset() the object is still owned by foo. But in some cases this is not good enough. This may create cyclic dependecies if A has shared_ptr to B and gives it a callback to A cyclic dependecy is created, so sometimes it would be useful to be able to provide weak bind function that is called iff the object exists -- that uses weak_ptr insteas of shared one. I has written a small draft of boost::weak_fn template<T> boost::weak_fn(void (T::*p)(...), weak_ptr<T> ptr) That creates such callback, it can be used with boost::bind similary to mem_fn: class foo { void bar(int x); }; Like: function<void(int x,int y)> f2=bind(weak_fn(&foo::bar,bar_ptr),_1+_2); function<void(int x)> f1=weak_fn(&foo::bar,bar_ptr); function<void()> f1=bind(weak_fn(&foo::bar,bar_ptr),0); The code availible from: http://art-blog.no-ip.info/files/weak_fn.tar.gz It is very initial implementation that gives functions from 0 to 3 parameters. - I just want to be sure if this is correct direction? - Comments on implementaions? Can it be done better? - Do I miss something? Thanks, Artyom

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Re: [boost] [Smart Ptr][Bind] Implementaion of Weak Callback Function
by Artyom 22 Mar '09

22 Mar '09

> foo = bind( &bar::slot, bind( > &weak_ptr<bar>::lock, weak_ptr<bar>( > bar_ptr ) ) ); > Such solution may work if you would write void bar::slot() { if(!this) return; // or if(!this) throw something(); } But I this is just a hack. More then that, throwing is not good idea because generally I do not want this situation be treated as a error. > However, one of those binds must be persisting the smart > pointer > somewhere, because calling foo always has an effect for me, > where I > would expect it to segfault after the shared_ptr is reset, > since > lock() would return a null shared_ptr. You might be able to > see the > problem though, and get where you want to be. Such "second" bind should return a "void" function that does nothing, that what I solve in weak_fn. Actually the code of weak_fn is quite simple (when using variadic templates, otherwise it is just many copies of same code for 0, 1 and N parameters). Suggestions? Comments? Artyom > > HTH, > Christopher > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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[gsoc]
by Matt 22 Mar '09

22 Mar '09

Hello, All I am Matthew Chandler, and I am looking to help out for the Google summer of code. I've looked through the ideas page and am interested in working on the Devector container. -Matt

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[C++0x] The cpp0x branch has been merged into trunk
by Beman Dawes 21 Mar '09

21 Mar '09

The cpp0x branch has been merged into trunk, enabling a bunch of BOOST_NO_* macros for C++0x feature tests. This should have no impact on existing code, so be sure to let me know if it causes any problems. --Beman

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[asio] possible multi-threaded bug with async_write_some()
by Brian and Victoria 21 Mar '09

21 Mar '09

I'm running asio (boost 1.38) multi-threaded, and noticed that on a context switch between threads, my handler for async_write_some() will sometimes get invoked with no data transferred. My handler would call async_write_some() again if there was remaining data, but this caused (most of) the data to get sent twice since there appears to still be a call to the handler pending in the work queue. I'm not sure if this behavior is a bug or not, but the solution was to check for 0 data transferred and exit the handler if so. -Brian

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threadpool lockfree_channel
by Tim Blechmann 21 Mar '09

21 Mar '09

hi oliver, i just saw, that you checked in a lockfree fifo implementation to the boost sandbox. it looks like an implementation of the michael/scott queue, isn't it? if so, i suppose, you are missing a thread-safe memory reclamation mechanism ... some time ago, i wrote a boost-style implementation of this data structure, not sure, if you came across it [1] ... maybe it would make sense to join our efforts in implementing a lockfree queue and get it into boost? best, tim [1] http://tim.klingt.org/git?p=boost_lockfree.git;a=summary -- tim(a)klingt.org http://tim.klingt.org Music is the can opener of the soul. It makes you terribly quiet inside, makes you aware that there's a roof to your being. Henry Miller

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[static] A useful static variable generator.
by Dongfei Yin 21 Mar '09

21 Mar '09

Hi, Some time, the sequence of static variable initialization always make something bad. the piece of code below will useful about this problem. class static_ { public: template <int N, class T> static T& var() { static T instance; return instance; } private: ~static_() {} }; so, if a static variable of std::string is wanted, I will use: static_::var<0, std::string>() = ":)"; the first template parameter is used for when many static variable of same type is needed. most important thing is all the variable will be initialized before use. Just for fun. Dongfei.

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[geometry] robustness approaches
by Fernando Cacciola 20 Mar '09

20 Mar '09

Hi boost geometers ;) When Barend first presented his geometric library proposal I argued that the so-called "epsilon-based" approach used by the library is just fundamentally wrong, and most importantly, totally unnecessary since much better methodologies exist. It deeply worries me to find that the GGL proposal haven't been updated in this regard, because the instrumentation of the proper techniques have a significant impact on the overall design. Robustness can't be treated as an implementation detail to be deal with later on (and I'm sorry if I haven't made this point clear when I warn about it before). If I where to review the library today I would have to strongly vote for rejection because of this. Here is a simple example of the fundamental problems I see all over the proposed library: There is a point_in_circle algorithm, which (as I can see from its implementation), essentially returns whether the distance from the point to the center is smaller than the circle radius. No doubt *that* is the one and only correct *mathematical* formulation for the predicate, but is one that just doesn't stand in practice at all. Computing *that very particular predicate ROBUSTELY* has been the subject of active research during the past decade, to such an extent, that pretty much every paper or article on the subject of robustness in geometric computing uses the in-circle test as a common example. The library proposed by Lucannus, OTOH, at least acknowledges the problem appropriately and approaches a solution in the right direction (there is still some important design-influencing considerations but are not showstopers) Here is a starting point http://www.mpi-inf.mpg.de/departments/d1/ClassroomExamples/ Best -- Fernando Cacciola SciSoft Consulting, Founder http://www.scisoft-consulting.com

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casting a shared_ptr from void with custom deleter
by Kenny Riddile 20 Mar '09

20 Mar '09

I'm trying to do something like this: boost::shared_ptr<const Foo> fooPtr( boost::static_pointer_cast<const Foo>(typeErasedFoo), CustomDeleter<const Foo>() ); where typeErasedFoo is of type: boost::shared_ptr<const void> The first statement compiles if I remove the custom deleter, but if I leave it in, I get errors saying: cannot convert parameter 2 from 'CustomDeleter<T>' to 'boost::detail::sp_enable_if_convertible_impl<true>::type' Is there any way to do what I'm trying to do? I no longer need typeErasedFoo after the cast if that helps.

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extending asio with unix signal handlers
by Dmitry Goncharov 20 Mar '09

20 Mar '09

Hi, What do you think of extending asio with unix signal handling? The extension lets the library user to have a handler invoked when a unix signal arrives. void on_signal(boost::system::error_code const& error) { if (!error) cout << "sigint received" << endl; } int main(int argc, char const* argv[]) { boost::asio::io_service ios; boost::asio::posix::signal_handler<SIGINT> sigint(ios); while (true) { ios.reset(); sigint.async_wait(boost::bind(on_signal, _1)); ios.poll(); } } This lets the user have a unix signal handler of an arbitrary signature. This also removes the "async-signal safe calls" restriction. Please, find the implementation along with two examples enclosed. BR, Dmitry

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Re: [boost] [gsoc][student] Proposal
by Kasra 20 Mar '09

20 Mar '09

> You're proposal has significant overlap with Crypto++ (public domain). >You might want to investigate some sort of code sharing, or at least > have a look at how they've done things. Thanks for mentioning Crypto++, I am aware of the library and have used it few time before (though it is a pain to compile and _link_). The library isn't exactly in public domain however, I have decided to use the algorithms code (i.e. mmx, sse2 instruction set and etc). The rest of boost.crypto library is designed to use templates over inheritance (the approach Wei Dai has used on Crypto++). With Best Regards --- Kasra Nassiri

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[fusion] compiler errors with empty boost::tuple
by Rutger ter Borg 20 Mar '09

20 Mar '09

I am experiencing a compiler error if I try to use a fusion join function on empty tuples. The operation I am trying to do does work with fusion::vectors. See attached; I guess this is a bug? Kind regards, Rutger ter Borg

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uploaded Channel - a lib for (distributed) message passing and event dispatching to boost vault
by Yigong Liu 20 Mar '09

20 Mar '09

Hello there, I just upload a updated version of my Channel library to Vault under Main/"Distributed Computing". This version contains some update for Channel to work with the latest boost distributions and change to boost license, since there are several requests for me to update and upload to Vault. A brief description: Channel procides name space for distributed message passing and event dispatching. Its major components (message IDs, routing algorithms...) are configurable as template parameters. As a namespace shared by peer threads, channels support publish/subscribe scope control, message filtering, and translation.. Thanks Yigong

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Question on ABI tags and autolinking
by Philip Lowman 20 Mar '09

20 Mar '09

Hi, I'm working on some cleanup of CMake's FindBoost module and had a few questions about Boost and it's ABI tags. 1. Are the ABI tags as defined on the webpage below always defined in this order in generated libraries? http://www.boost.org/doc/libs/1_38_0/more/getting_started/windows.html#libr… 2. Regarding the "-s" ABI tag, the current CMake module has a deficiency and only searches for it under Windows and only after not being able to find a non "-s" library there. On other platforms it doesn't search for the "-s" at all. I'm curious what the defaults are for building Boost against static C/C++ system libraries using Boost's present build system? Does this happen on compilers other than VS? I just want to know if there is any history to this oddity or if it's just a bug. 3. Are "-p", "-n", and "-y" ABI tags persistent across all generated libraries filenames once one of them is enabled? In other words, the generated Boost library filenames vary only on "-s" (static runtime) , "-g" (debug standard/runtime libs) , and "-d" (debug build of boost library)? 4. None of this changes (or will change) under the CMake build of Boost, I trust? 5. Is there a consolidated list of Boost libraries online for which MSVC/Borland/etc. auto-linking is always against the shared library? I'd like to be able to link the end-user to a list of these, if possible. Thanks. -- Philip Lowman

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[tuple][io] compiler error on empty tuple
by Rutger ter Borg 19 Mar '09

19 Mar '09

Apparently boost::tuple's io-support doesn't include empty tuples. See attached, this results in a compiler error using g++ 4.3.3. I think it shouldn't give an error, since "b" is a valid instance. Kind regards, Rutger ter Borg

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