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99 Bottles of Beer using Boost MPL, feedback invited
by Alastair Rankine 07 Aug '11

07 Aug '11

So inspired by http://programmingpraxis.com/2011/08/05/ninety-nine-bottles-of-beer/ , I decided to attempt to generate the lyrics to the 99 bottles of beer song. To make it interesting I decided to use Boost MPL to generate the lyrics using template metaprogramming. Here is my attempt. https://gist.github.com/1130306 It compiles with gcc 4.2 against boost 1.47. Given that I am pretty inexperienced with MPL I would very much appreciate some constructive criticism. I'd specifically like to know if the code can be cleaned up to be simpler or to perform better. Also I'm not entirely happy with the duplication in the PrintX functors, would definitely like to get a better approach here. Thanks,

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[Fusion] Is there an assignment function for any two conformant sequences?
by someguy 07 Aug '11

07 Aug '11

Is there a function like "assign(dest_fusion_seq,src_fusion_seq)" which does recursive element-wise assignment between any two conformant fusion sequences(including adapted ones)? I didn't find one but I think there should be such functionality. -- View this message in context: http://boost.2283326.n4.nabble.com/Fusion-Is-there-an-assignment-function-f… Sent from the Boost - Users mailing list archive at Nabble.com.

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[Boost.Serialization] Serializing "abstract" classes
by Júlio Hoffimann 06 Aug '11

06 Aug '11

Dear all, I'm using Boost 1.45... I've read Boost.Serialization docs so many times and can't understand why my testcase is not working as expected. According to the following three links, we need to address serialization of derived classes with "abstract" base class by using boost macros: http://www.boost.org/doc/libs/1_47_0/libs/serialization/doc/traits.html#exp… http://www.boost.org/doc/libs/1_47_0/libs/serialization/doc/special.html#ex… http://www.boost.org/doc/libs/1_47_0/libs/serialization/doc/traits.html#abs… I did my testcase ( http://codepad.org/6ETp1Ac0 ) completely based on the demo: http://www.boost.org/doc/libs/1_47_0/libs/serialization/example/demo.cpp Compiling and running shows that the derived class archive contains just the base class data members. What is happening? How can i solve this problem? I really appreciate any help, Júlio.

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Another baffling error message
by Eric Fowler 06 Aug '11

06 Aug '11

Sorry to have to ask the list for help, but I am once again stumped. Perhaps you will find this easy. I have some classes defined: using namespace std; using namespace boost; class POS{..stuff..} class LEN{...stuff...} typedef adjacency_list<vecS, vecS, undirectedS, POS, LEN> DG; typedef graph_traits<DG>::vertex_descriptor Vertex; typedef graph_traits<DG>::edge_descriptor Edge; class DelaunayGraph: public DG { public: void foo() { Edge e = whatever(); remove_edge(e, *this); // <<<<----THIS BLOWS UP ..stuff... } The error I am getting is: c:\documents and settings\eric\my documents\visual studio 2008\projects\shuttle\delaunay\trunk\delaunaygraph.h(371) : error C2661: 'boost::undirected_graph_helper<Config>::remove_edge' : no overloaded function takes 2 arguments with [ Config=boost::detail::adj_list_gen<boost::adjacency_list<boost::vecS,boost::vecS,boost::undirectedS,POS,LEN>,boost::vecS,boost::vecS,boost::undirectedS,boost::property<boost::vertex_bundle_t,POS>,boost::property<boost::edge_bundle_t,LEN>,boost::no_property,boost::listS>::config ] What am I doing wrong in this instance, and what design principle am I violating? Eric

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datetime will not be parsed
by Kraus Philipp 06 Aug '11

06 Aug '11

Hello, I use this code for parsing a string into a datetime: boost::local_time::local_date_time l_datetime(boost::date_time::not_a_date_time); std::istringstream l_datestream("Sat Aug 06 10:52:26 +0000 2011"); l_datestream.imbue( std::locale( std::locale::classic(), new boost::local_time::local_time_input_facet("%a %b %d %H:%M:%S %q %Y")) ); l_datestream >> l_datetime; But the l_datetime is always set to "not a date time". I think the parameter within the input facet are correct, so I don't understand why the string is not be parsed. Can anyone help me please to create a working solution? Thanks Phil

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question about boost::intrusive_ptr
by Mahmood Naderan 06 Aug '11

06 Aug '11

Hi I used boost::intrusive_ptr in a function, say foo(), like this: boost::intrusive_ptr<BranchFeedback> theFeedback ( new BranchFeedback() ); std::vector< std::vector< BPredState > > theFetchState; .... theFeedback->theBPState = &theFetchState[anIndex][!anOne]; The difinition of BranchFeedback and BPredState are: struct BranchFeedback : boost::counted_base { ... boost::intrusive_ptr<BPredState> theBPState; }; struct BPredState : boost::counted_base { ... uint32_t theGShare; uint32_t theSerial; }; The problem is when foo() reaches the end (I mean '}'), I get segmentation fault which points to ~intrusive_ptr() { if(p_ != 0) intrusive_ptr_release(p_); } I thought I used the intrusive_ptr in a correct way. Is there any consideration that I missed? Thanks, // Naderan *Mahmood;

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is boost 1.46.1 contain thread/read_write_mutex.hpp
by Eric Lin 05 Aug '11

05 Aug '11

dear boost progamers: when I tried to compile from my g++4.5.2 a simple file which include #include <boost/thread/read_write_mutex.hpp> ------- root@eric-laptop:/home/eric/cppcookbook/ch12# g++ -lboost_thread Example12-3.cpp Example12-3.cpp:3:45: fatal error: boost/thread/read_write_mutex.hpp: No such file or directory compilation terminated. --------- and I check from / of my ubuntuLinux with boost 1.46.1 I can not find any file name as read_wirte_mutex.hpp --------- root@eric-laptop:/# find . | grep read_write_mutex.hpp root@eric-laptop:/# --- and I can not digout from web how to make it compile under gcc/g++ plz help, Eric

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synchronize threads from a thread pool (using asio::io_service)
by Daren Lee 05 Aug '11

05 Aug '11

Hi - I'm using asio::io_service as a dispatcher for a thread pool. I'm wondering how I can synchronize the threads after I post the tasks to the io_service. I tried using a barrier but it doesn't always work correctly. The barrier waits indefinitely; although I verified the post() function gets called, the io_service doesn't seem to dispatch anything. I've also thread using the boost::threadpool library but the overall speed is slower. I'd appreciate any insight on what I'm doing wrong with the barrier or any other high performance thread pooling alternatives. Thanks, Daren <code> void handler ( int i, int nSize, double *pArray, double *pTemp, boost::barrier *pBarrier ) { // compute on pArrray --> write result to pTemp[i] .... pBarrier->wait(); } double doCalc ( int nSize, double *pArray, double *pTemp ) { unsigned int nNumThreads = 8; int nSubSize = nSize / nNumThreads; boost::barrier barrier( nNumThreads + 1 ); for( int i=0;i<nNumThreads;i++ ) { if( i == nNumThreads-1 ) { m_io_service.post( boost::bind( &handler, i, nSize-(i*nSubSize), pArray+(i*nSubSize), pTemp, &barrier )); } else { m_io_service.post( boost::bind( &handler, i, nSubSize, pArray+(i*nSubSize), pTemp, &barrier )); } } barrier.wait(); // sum results double fSum = 0; for( int i=0;i<nNumThreads;i++ ) { fSum += pTemp[i]; } return fSum; } I initialize the io_service with work elsewhere as: boost::asio::io_service::work m_work( m_io_service ); boost::thread_group m_threads; for (std::size_t i = 0; i < m_nNumThreads; ++i) m_threads.create_thread(boost::bind(&boost::asio::io_service::run, &m_io_service)); </code>

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What's wrong with this simple multithreaded function that uses regex?
by Andrew Yancy 05 Aug '11

05 Aug '11

The code snippet below is the core of a function mythreadfunc() that is run concurrently for several threads using the Win32 MSVC functions CreateThread() and WaitForMultipleObjects(). Everything seems to work fine except for actually using boost::regex_match(). For example, if that line below is changed to if(true), the entire multithreaded function works perfectly. Similarly, if mythreadfunc() as shown below is run without multiple threads, it works perfectly. But if mythreadfunc() as shown below is run with multiple threads, the entire program crashes with return value 0xc0000005, which is some kind of memory access violation. This leads me to believe that boost::regex does not play well with MSVC threads, but according to the Boost site, there aren't any bugs related to this issue for Boost 1.45. As far as I can tell I'm using Boost in thread safe mode (BOOST_HAS_THREADS is defined). I'm probably doing something really dumb related to MSVC threads or related to the way I configured Boost, but I'm not sure what it is! I could switch to using Boost threads, but I would like to minimize the changes to the code. Thanks very much for any help~ ... static const boost::regex expression("^[0-9]+"); ifstream myfile(x); //x is a different file name for every thread string line; if(myfile.is_open()) { while(myfile.good()) { getline(myfile, line); if(boost::regex_match(line, expression)) { //do stuff } } myfile.close(); } ...

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[Filesystem] There must be a better way to do path decomposition
by Ramon F Herrera 04 Aug '11

04 Aug '11

This code at least works: string directory_path(argv[1]); path p(directory_path); ostringstream component; string lastComponent; for (path::iterator it = p.begin(); it != p.end(); it++) { component.str(""); // Hack, to be replaced by better way component << *it; // to grab `*it' in a string lastComponent = component.str(); } lastComponent = lastComponent.substr(1, lastComponent.size()-2); According to the documentation examples, the item pointed to by `*it' is of the following type: path::iterator::value_type is path::string_type, and iteration treats path as a container of filenames. I tried to capture `*it' in a string and in a string_type but the compiler does not like the '=' operator. TIA, -RFH

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