May 2009 - Boost-users - lists.preview.boost.org

[Accumulators] Are all statistics lazily evaluated by default?
by pete＠pcbartlett.com 14 May '09

14 May '09

Hi all, I really like the range of statistical properties that the accumulators library supports but am a little unclear about the laziness properties of the library. Suppose I wish to offer a interface that lets the user send a bunch of data and request the k-th moments where k is specified by the user at runtime. Will the accumulator_set accumulator_set< value_type , ba::tag::moments > acc; where k_max >= k (but the inequality may be strict) be efficient. I.e. I only do the calculations necessary to get the k-th moment not the k-max-th? The reason I ask is the documentation makes a distinction between variance and lazy_variance, but this distinction does not seem to be made for other statistics. Thanks in advance for any assistance, Pete

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(Boost.Python) How to print from C++ to the same stream as Python's 'print' does?
by Dietrich Bollmann 14 May '09

14 May '09

Hi, I would like to print from C++ to the same stream as Python's 'print' command does. I am using an embedded Python shell and when using std::cout nothing is printed at all... Currently I am using the following code: std::ostringstream oss; oss << "test\n"; std::string cs = oss.str(); PySys_WriteStdout(cs.c_str()); I wonder if there is an easier way to get the same result? Thanks, Dietrich

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Re: [Boost-users] Tips on implementing a function queue with unique queue items (compare function problem)
by Peter Åberg 14 May '09

14 May '09

Excellent, spot on, thanks gurus :-) /Peter Åberg Steven Watanabe wrote: > If the caller of push knows the type of the function object, > then you can template the push function. > > template<class F> > void push(const F& f) { > if(std::find_if(queue.begin(), queue.end(), f == _1) != queue.end()) { > queue.push_back(item); > } > } > > This is going to be pretty inefficient because of the linear search, > but the same idea applies if you want to store the function objects > in a data structure that supports faster lookup. > > In Christ, > Steven Watanabe > > Nat Goodspeed Wrote: > You're right that we can't compare two boost::function objects, but it > *is* permitted to compare a boost::function with an rvalue that could > initialize it. If you make your push() method a template accepting an > argument of arbitrary type, presumably you could compare each existing > item with that new value before storing it into the deque. > >

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[test] boost::test equivalent of CppUnit's "protectors" ?
by Tim Day 14 May '09

14 May '09

I've used both CppUnit and boost::test for C++ unittesting. Generally I prefer boost::test, mainly because the auto-test macros minimise the effort to setup tests. But there's one thing I really miss from CppUnit: the ability to register your own custom "protectors", instances of which automatically wrap all the run tests. (Technically, you install a test "listener", and that can wrap each test run in a protector scope. Multiple listeners and nested protectors are possible). I've found these invaluable in the past for monitoring unittests for unexpected side effects (e.g checking code hasn't changed the floating-point unit state flags, or messed with other global state). I can't see any equivalent in the boost::test documentation, although BOOST_FIXTURE_TEST_CASE maybe comes closest. (However, whereas a CppUnit protector can return a bool to indicate pass/fail, it's less clear to me how a fixture destructor should indicate failure). Any suggestions for how to best achieve the same thing as CppUnit's protectors in boost::test (and without updating the body of each test) ? Thanks for any advice Tim

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date_time\gregorian\conversion.hpp : fatal error C1001 MSVC 7.1
by Wilkinson, John (Software) 14 May '09

14 May '09

I get the following error with boost 1.39 and MSVC 7.1 SP1 when including <boost/thread/thread.hpp>. c:\boost_libs\V1_39_0\boost\date_time\gregorian\conversion.hpp(43) : fatal error C1001: INTERNAL COMPILER ERROR (compiler file 'msc1.cpp', line 2708) Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information This problem was in 1.38 as reported here http://archive.netbsd.se/?ml=boost-users&a=2009-02&t=9851835. I was wondering should I raise a bug? I have searched the bugs database but cannot find it already there. Also can anyone suggest a work-around? Turning the browse facility off is not an option; it is a feature I often use. Thanks John <DIV><FONT size="1"> E-mail confidentiality. -------------------------------- This e-mail contains confidential and / or privileged information belonging to Spirent Communications plc, its affiliates and / or subsidiaries. If you are not the intended recipient, you are hereby notified that any disclosure, copying, distribution and / or the taking of any action based upon reliance on the contents of this transmission is strictly forbidden. If you have received this message in error please notify the sender by return e-mail and delete it from your system. If you require assistance, please contact our IT department at helpdesk(a)spirent.com. Spirent Communications plc Northwood Park, Gatwick Road, Crawley, West Sussex, RH10 9XN, United Kingdom. Tel No. +44 (0) 1293 767676 Fax No. +44 (0) 1293 767677 Registered in England Number 470893 Registered at Northwood Park, Gatwick Road, Crawley, West Sussex, RH10 9XN, United Kingdom. Or if within the US, Spirent Communications, 26750 Agoura Road, Calabasas, CA, 91302, USA. Tel No. 1-818-676- 2300 </FONT></DIV>

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Boost gzip_decompressor - compilation errors
by einav_i2 14 May '09

14 May '09

Hi! I'm trying to compile the following function on Boost 1.34.1 (Ubuntu 8.04): void decompress(string &gzipString, string & target) { boost::iostreams::filtering_ostream decompressingStream; boost::iostreams::gzip_decompressor gzdc; decompressingStream.push(gzdc); decompressingStream.push(boost::iostreams::back_inserter(target)); decompressingStream << gzipString; boost::iostreams::flush(decompressingStream); } And I'm getting the following (quite long) error: /usr/include/boost/iostreams/chain.hpp: In member function ‘void boost::iostreams::detail::chain_base<Self, Ch, Tr, Alloc, Mode>::push_impl(const T&, int, int) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Self = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >, Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, Mode = boost::iostreams::output]’: /usr/include/boost/iostreams/chain.hpp:207: instantiated from ‘void boost::iostreams::detail::chain_base<Self, Ch, Tr, Alloc, Mode>::push(const T&, int, int, typename boost::disable_if<boost::iostreams::is_std_io<T>, void>::type*) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Self = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >, Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, Mode = boost::iostreams::output]’ /usr/include/boost/iostreams/chain.hpp:465: instantiated from ‘void boost::iostreams::detail::chain_client<Chain>::push_impl(const T&, int, int) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Chain = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >]’ /usr/include/boost/iostreams/chain.hpp:453: instantiated from ‘void boost::iostreams::detail::chain_client<Chain>::push(const T&, int, int, typename boost::disable_if<boost::iostreams::is_std_io<T>, void>::type*) [with T = boost::iostreams::gzip_decompressor, Chain = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >]’ main.cpp:93: instantiated from here /usr/include/boost/iostreams/chain.hpp:233: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ /usr/include/boost/iostreams/stream_buffer.hpp: At global scope: /usr/include/boost/iostreams/stream_buffer.hpp: In instantiation of ‘boost::iostreams::stream_buffer<boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, std::char_traits<char>, std::allocator<char>, boost::iostreams::output>’: /usr/include/boost/iostreams/chain.hpp:246: instantiated from ‘void boost::iostreams::detail::chain_base<Self, Ch, Tr, Alloc, Mode>::push_impl(const T&, int, int) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Self = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >, Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, Mode = boost::iostreams::output]’ /usr/include/boost/iostreams/chain.hpp:207: instantiated from ‘void boost::iostreams::detail::chain_base<Self, Ch, Tr, Alloc, Mode>::push(const T&, int, int, typename boost::disable_if<boost::iostreams::is_std_io<T>, void>::type*) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Self = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >, Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, Mode = boost::iostreams::output]’ /usr/include/boost/iostreams/chain.hpp:465: instantiated from ‘void boost::iostreams::detail::chain_client<Chain>::push_impl(const T&, int, int) [with T = boost::iostreams::basic_gzip_decompressor<std::allocator<char> >, Chain = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >]’ /usr/include/boost/iostreams/chain.hpp:453: instantiated from ‘void boost::iostreams::detail::chain_client<Chain>::push(const T&, int, int, typename boost::disable_if<boost::iostreams::is_std_io<T>, void>::type*) [with T = boost::iostreams::gzip_decompressor, Chain = boost::iostreams::chain<boost::iostreams::output, char, std::char_traits<char>, std::allocator<char> >]’ main.cpp:93: instantiated from here /usr/include/boost/iostreams/stream_buffer.hpp:66: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ A similar "compress" function seem to compile without any problems. Any ideas what can cause this error? Thanks, Einav -- View this message in context: http://www.nabble.com/Boost-gzip_decompressor---compilation-errors-tp235353… Sent from the Boost - Users mailing list archive at Nabble.com.

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Serialization / Fast [non-portable] serialization for binary data
by Dan Eaton 14 May '09

14 May '09

Hi, One more question for the list: I have my own 1, 2 and 3 dimensional array classes, and would like to serialize large such objects quickly. In other words, for( unsigned i=0; i<some_large_dynamic_number; i++ ) ar & ptr[i]; is not desirable (or perhaps modern compilers actually do a sufficiently good job at optimizing this case? opinions?) Is this a case where I'd be better to specialize my "serialize" method for both text_?archive (portable) and binary_?archive (fast), and then further split the binary case into save/load, which would in turn invoke save_binary and load_binary (as appropriate)? In this case (assuming the above is right, and out of curiosity) why is there no "serialize_binary" method instead of separate save/load_binary methods? I'm thinking that with this method, there would be no need to split "serialize" into "save"/"load" for this case... Thank you, Danny

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multi-index-container with nested templates => problem getting iterator on 2nd index.
by JohnQ 14 May '09

14 May '09

Hi, I'm really stuck on this one, so I'm hoping someone can lend me a hand. Basically, I'm defining a templated multi-index-container to hold one piece of data along with two indexes to that data. Next, I'm wrapping that in another templated class that will handle concurrent access to that structure. My problem is that I'm having trouble figuring out how to define a type that will give me an interator on the 2nd index of the multi-index-container ("bimimapIterator2" below). I'm basing this on the Boost multi-index-container example here: http://www.boost.org/doc/libs/1_39_0/libs/multi_index/example/bimap.cpp Here's what I have... //******************************************************************** // multi-index-container //******************************************************************** struct index1{}; struct index2{}; template<typename Key1,typename Key2, typename Data> struct bimultimap { typedef boost::tuple<Key1,Key2,Data> value_type; typedef boost::multi_index_container< value_type, indexed_by< ordered_non_unique< tag<index1>,member<value_type,Key1,&value_type::first> >, ordered_non_unique< tag<index2>,member<value_type,Key2,&value_type::second> > > > bimimap; }; //******************************************************************** // concurrent access class. //******************************************************************** template<typename Key1, typename Key2, typename Data> class concurrent_bimultimap { private: typename bimultimap<Key1, Key2, Data>::bimimap the_bimultimap; mutable boost::mutex the_mutex; boost::condition_variable the_condition_variable; public: typedef typename bimultimap<Key1,Key2,Data>::bimimap bimimapType; typedef typename bimultimap<Key1,Key2,Data>::bimimap::iterator bimimapIterator; typedef typename bimultimap<Key1,Key2,Data>::bimimap::index<index2>::type::iterator bimimapIterator2; void insert(Key1 const& key1, Key2 const& key2, Data const& data) { boost::mutex::scoped_lock lock(the_mutex); the_bimultimap.insert( bimultimap<Key1,Key2,Data>::bimimap::value_type(key1,key2,data) ); lock.unlock(); // Note: because we unlock above and notify below, we can starve the "pop" thread for short durations in burst situations. That's ok so far. the_condition_variable.notify_one(); } bool findKey1(Key1& key1, Data& data) { boost::mutex::scoped_lock lock(the_mutex); bimimapIterator itFindIt = the_bimultimap.find(key1); if (itFindIt != the_bimultimap.end()) { data = itFindIt->third; return true; } else return false; } bool findKey2(Key2& key2, Data& data) { boost::mutex::scoped_lock lock(the_mutex); bimimapIterator2 itFindIt = the_bimultimap.get<index2>().find(key2); if (itFindIt != the_bimultimap.get<index2>().end()) { data = itFindIt->third; return true; } else return false; } ..... there's more but this gives the essence of the problem .... };

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Bidirectional Graph and undirected graphs
by Daniel Russel 14 May '09

14 May '09

I'm trying to add the needed functions to make one of our graphs work as a boost graph and ran into a contradiction in the docs: The introduction to bidirectional graph says "For undirected graphs this [need for extra information] is not an issue, since the in_edges() and out_edges() functions are the same, they both return the edges incident to the vertex." however the function docs for in_edges say: "For both directed and undirected graphs, the target of an out-edge is required to be vertex v and the source is required to be a vertex that is adjacent to v." The latter implies that undirected graphs have to have two copies of each edge, one pointed each direction. Which is correct? The former, I hope :-) Thanks.

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boost:statechart: How can I access the state machine from within a custom error handler?
by Jale Gulea 13 May '09

13 May '09

Hello, I have replaced the null_exception_translator (http://www.boost.org/doc/libs/1_34_1/libs/statechart/doc/reference.html#nul…) with one of my own brew and I cannot figure a way to get the state machine in the context of which the the handler gets called. The 'machine_' member is private in both the 'Action' and the 'ExceptionEventHandler'. The 'translator_' is also private - thus inaccessible in my derived state machine. Any ideas are appreciated. Kind regards /JG

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