January 2010 - Boost-users - lists.preview.boost.org

Non-Boost question: HTML parser with hpricot
by Boost lzw 09 Jan '10

09 Jan '10

Hi folks, Sorry for posting a question unrelated to boost. I know pretty well that boost has perfect solutions to it. But I am working on a legacy system using Hpricot of Ruby on Rail. So only Hpricot-specific suggestions please. Thank you. In my HTML parser, I can parse a html file with the following hpricot commands: (1) doc = open( "MyFileToParse.html" ) { |f| Hpricot(f) } (2) elements = (doc.search("/html/body/table/tr/td/table/tr/td/font") ) (3) puts (elements[13]).inner_html to get the following output: Giaever G, et al (2002). Functional profiling of the Saccharomyces c erevisiae genome. Nature, 418:387-91. [<a href=" http://www.ncbi.nlm.nih.gov/entr ez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12140549&dopt=Abstract" target="_ blank">PubMed</a>] How can I proceed to get the following results (3) and (4) respectively? (3) Giaever G, et al (2002). Functional profiling of the Saccharomyces c erevisiae genome. Nature, 418:387-91. (4) http://www.ncbi.nlm.nih.gov/pubmed/12140549?dopt=Abstract NOTE: to get (4) I need to take two more steps: (5) replace "&" with "?" (6) replace "PubMed" with "pubmed" (this might be trivial, but how?) in the process of parsing in addition to "normal" HTML parsing. Thanks a lot in advance. Robert

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Problem with boost::thread::sleep
by Rob Yull 08 Jan '10

08 Jan '10

Using Boost 1.41, MSVC 2005, Win 7 x64 (compiling 32-bit). I was trying to set a small delay in a loop, so the loop doesn't consume all of the processor, using boost::thread::sleep(). I tried using the example from the threading documentation (http://www.boost.org/doc/libs/1_41_0/doc/html/thread/time.html#thread.time. get_system_time): boost::thread::sleep(boost::posix_time::milliseconds(25)); I keep getting a compiler error from the line above. Error 2 error C2664: 'boost::thread::sleep' : cannot convert parameter 1 from 'boost::date_time::subsecond_duration<base_duration,frac_of_second>' to 'const boost::system_time &' Is there something else I need to be doing to make this work? -Rob Yull

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Automatic thread join
by Lloyd 08 Jan '10

08 Jan '10

Hi, Is there a way to join a thread automatically to the main thread when it finishes execution? In my case, the main thread does not call the "thread->join()", so even if the work of the thread is over, the thread never joins to the main thread. What is the technique usually used to make a thread join to its main thread, so as to avoid wastage of resources. Thanks, Lloyd ___________________ Happy New Year 2010

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boost::crc - newbie help
by Paul Caswell 08 Jan '10

08 Jan '10

Hello all, I've the task of implementing the following CRC computation and was wondering whether I could use boost::crc to save me a lot of hassle. ------------------------ Default 32-bit Parity (CRC) This 32-bit CRC is the same as that described in EKMS 304 ([6]) and EKMS 322 ([8]) and could be used as a CRC method in the keyAlgorithm Attribute (with OID { 1 2 826 0 1145 0 5 1 }). Let g(x) be the polynomial x32 + x22 + x2 + x + 1. Let d(x) be the k bits of data to have parity applied to them. The first bit of data is the coefficient of the (k-1)st power of x etc. Let f(x) be the polynomial naturally represented by the initial fill 0xF8DD4258, i.e. x31 + x30 + x29 + x28 + x27 + x23 + x22 + x20 + x19 + x18 + x16 + x14 + x9 + x6 + x4 + x3. Then the output is c(x) = x32d(x) + xkf(x) mod g(x). The polynomial c(x) is then interpreted as a stream with the coefficient of x31 coming first and the coefficient of x0 coming last. The 32-bit parity is then c(x). This calculation can be done using a simple shift register as shown below. The shaded stages represent ones in the initial fill. The logic steps k times to determine c(x), which is the final state of the register. <diagram omitted> ------------------------ Any advice and or help would be appreciated. Regards, Paul This email and any files transmitted with it may be confidential, legally privileged and protected in law and are intended solely for the use of the individual to whom it is addressed. Any view or opinions presented are solely those of the author and do not necessarily represent those of Stonewood Group Ltd. If you have received this Email in error please contact the sender by return and confirm that its contents have been destroyed without further distribution or disclosure. Please email admin(a)stonewood.co.uk with any questions relating to this disclaimer. Stonewood Group Ltd has Registered Offices at Sandford Lane, Wareham, Dorset BH20 4DY. The company is registered in England and Wales under no: 3007498.

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Thread not interrupted in runtime linked library
by Lloyd 08 Jan '10

08 Jan '10

Hi, Using boost thread a new thread is created. The thread loads a DLL using LoadLibrary() call, gets the procedure address by calling GetProcAddress() and executes the procedure. The body of procedure is an infinite loop. When I try to interrupt the thread from main thread it is not interrrupted! What could be the reason? In all other cases the thread is interrupted except when it is inside the dynamically (runtime) linked library procedure. What could be the reason? Please share some idea... Thank you very much Lloyd ___________________ Happy New Year 2010

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Xpressive continuing search from previous match
by K. Noel Belcourt 08 Jan '10

08 Jan '10

Hi, I have a search for a regular expression like this. sregex_iterator cur(buffer.begin(), buffer.end(), defined_re), end; for(; cur != end; ++cur) { ... But what I really want to do is perform a new regex search starting at the location in the buffer marking the end of the previous search. Is there a way to get the buffer index from the previous search so I can start the new search past the previous search? I apologize if this is easy to do, I must have missed it with my quick perusal through the documentation. Thanks. -- Noel Belcourt

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Defining Statements with Proto
by David A. Greene 08 Jan '10

08 Jan '10

A few years ago, I asked how to define a grammar with Proto to match something like this: if_(expr) [ stmt, stmt, ... ].else [ stmt, stmt, ... ]; The answer was to do this: struct Grammar; struct ExpressionGrammar; struct StatementGrammar; struct Domain; template<typename Expr> struct Expression : proto::extends<Expr, Expression<Expr>, Domain> { typedef proto::extends<Expr, Expression<Expr>, Domain> base_type; Expression(Expr const & expr = Expr()) : base_type( expr ) {} }; struct Domain : proto::domain< proto::generator< Expression >, Grammar> {}; struct If {}; BOOST_PROTO_DEFINE_FUNCTION_TEMPLATE( 1 , if_ , Domain , (If) , BOOST_PP_SEQ_NIL ); // Here is the grammar for if_ statements // matches if_(e1)[e2] struct IfGrammar : boost::proto::subscript< boost::proto::arg< boost::proto::unary_expr< If, ExpressionGrammar >, >, StatementGrammar > {}; // An else_ "operator" template<typename Expr> struct Expression< Expr , typename enable_if<proto::matches<Expr, IfGrammar> >::type > : proto::extends<Expr, Expression<Expr>, Domain> { Expression() : else_(proto::make_expr<Else>(*this)) {}; proto::result_of::make_expr< Else, // else is now an "operator" Expression<Expr> const >::type const else_; }; // matches if_(e1)[e2].else_[e3] struct IfElseGrammar : boost:proto::subscript< boost::proto::arg< boost::proto::unary_expr< Else, IfGrammar >, >, StatementGrammar > {}; I didn't understand it then and I don't now. :) However, it seems to be obsolete since BOOST_PROTO_DEFINE_FUNCTION_TEMPLATE doesn't seem to exist anymore (it's not documented, anyway). So how would this be formulated in modern Boost.Proto? I'm guessing I will need an expression template wrapper (called Expression<> above) that uses some combination of BOOST_PROTO_BASIC_EXTENDS, BOOST_PROTO_EXTENDS_SUBSCRIPT and BOOST_PROTO_EXTENDS_FUNCTION. But of course not all statements have a valid operator() overload and no expressions do. I guess the grammar will take care of that, yes? I'm really puzzled about how to do the ".else_" part. I was hoping I could look to Phoenix to get a clue but it doesn't seem to use Proto. Any help? Thanks! -Dave

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[foreach] BOOST_FOREACH question...
by barcaroller 08 Jan '10

08 Jan '10

Does the BOOST_FOREACH macro work for empty sequences or must a size check be done explicitly? list<int> mylist; if (!mylist.empty()) // <--- necessary? { foreach(int& i, mylist) { // take action } } The reason I ask is that neither begin() nor end() return valid iterators for empty sequences, but it is my understanding that BOOST_FOREACH needs iterators to work properly.

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fusion and mpl
by Peter Foelsche 08 Jan '10

08 Jan '10

I need to be able to convert a mpl sequence into something like a tuple: typedef boost::mpl::vector<double> CMplSequence; typedef CCreateVectorFromMpl<CMplSequence>::type CVector; I need to have runtime access with constant index: CVector s; get<0>(s) = 1.0; std::cout << get<0>(s) << "\n"; I need to be able to retrieve the type at compile time: typedef CGetType<CVector, boost::mpl::long_<0> >::type CFirstType; I already wrote something like this using std::pair as the tuple but I'm running into problems storing reference types on Windows. Peter

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boost::multi_array equivalent for runtime number of dimensions
by Hicham Mouline 07 Jan '10

07 Jan '10

Hello, I only know at runtime the dimension and extends of a multidimensional array, though the number of dimensions is always < 10 for e.g. Is there a container that allows this? Otherwise, I can write code for multi_array<T, 2> multi_array<T, 3> . multi_array<T, 10>, do a switch case on the dimensions variable, and select the appropriate code, regards,

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