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Re: [Boost-users] Newbie question: Random numbers.
by james.jones＠firstinvestors.com 19 May '06

19 May '06

From: Greg Link <link(a)cse.psu.edu> > One particularly effective technique is to seed it once, and only > once. Iterate (through the random stream) a bit, then save that value > to a file. Anytime your program closes, just grab one last number > from the stream, save it to the file, and re-load that as your next > seed. This is a clever idea, but I think it has some problems. First, if you do this, *protect the file very carefully*. Because if its contents are known and your random numbers are used for any sort of security, suddenly your system is not secure at all. Secondly, you must ensure that the program *always* changes the file, or else you will get two identical runs. This may be annoying or actually dangerous depending on context. A good technique for always changing the file would be to read the contents, then delete it before doing anything with it. On exit, write the file again. Thirdly, this method assumes that the program only gets run once at a time. What if it's running in two separate processes at the same time? If you don't delete the file as I suggest above, then both processes have the same seed - probably a bad idea. If you do delete the file, then the second process has to generate a new seed and the file did no good. - James Jones Administrative Data Mgmt. Webmaster 375 Raritan Center Pkwy, Suite A Data Architect Edison, NJ 08837

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[serialization] BOOST_CLASS_IMPLEMENTATION(*, object_serializable), can this effect be somehow achieved globally for all classes?
by Peter Schregle 19 May '06

19 May '06

I've discovered the BOOST_CLASS_IMPLEMENTATION macro, which allows me to use object_serializable in order to remove extra bookkeeping information for a single class in the archive. Is there a way to apply this effect for all classes in my project globally? I want to avoid the need to type this macro in a thousand times for my project. Best regards Peter

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[serialization] How to serialize as an XML attribute?
by Peter Schregle 19 May '06

19 May '06

Is it thinkable that some values could be serialized as XML attributes and not as XML elements? Where would be the correct place to add this functionality? I'm thinking to override the nvp and xml_archive. Is this the correct place to look at? Best regards Peter

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finding documentation & reference
by HeroreV 19 May '06

19 May '06

The documentation at boost.org is quite confusing. I just spent way too much time trying to figure out how to get a ptr_vector to let go of anything without destroying it or giving control to another ptr_vector. The page at http://boost.org/libs/ptr_container/doc/ptr_vector.html doesn't say a single word about release(). The page also makes ptr_vector appear to only inherit from ptr_sequence_adapter which also mentions nothing about release(). It wasn't until I went to the examples page at http://boost.org/libs/ptr_container/doc/examples.html that I saw anything about release(), and even then it was barely passed over so it took a few minutes more of guessing to get things working. Is there a good reference list that shows all member functions of the various boost classes? Or any advice on how I'm supposed to use the documentation? I really don't know how I'm supposed to learn boost when key features aren't mentioned, unless users are expected to go through all the source to ever learn anything. - HeroreV

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Re: [Boost-users] Newbie question: Random numbers.
by Andrew Holden 19 May '06

19 May '06

My first thought is that you probably shouldn't reinitialize the generator for every random number you need. I would recommend that you create and seed "generator" once at the start of your program, then reuse it whenever you need a random number. Perhaps something like the following: namespace Random { typedef boost::minstd_rand base_generator_type; typedef boost::uniform_int<> distribution_type; typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type; //Declare the generator as a global variable for easy reuse base_generator_type generator(static_cast<unsigned long>(clock())); /*************************************************** * initializes the random number generator * **************************************************/ void initialize() { for (int i = 0; i < 30000; ++i) generator.seed(static_cast<unsigned long>(clock())); } /*************************************************** * generates a random number between a and b * * @param a the starting range * * @param b the integer ending range * * @return N such that a <= N <= b * **************************************************/ template <class T> T rand_int (const T& a, const T& b) { //Check the parameters BOOST_STATIC_ASSERT(boost::is_integral<T>::value); assert (b >= a); //Set up the desired distribution gen_type ran_gen(generator, distribution_type(a, b)); //Get a random number return ran_gen(); } } using Random::rand_int; int main(int argc, char* argv[]) { Random::initialize(); std::cout << rand_int (1,1000) << std::endl << rand_int (1,1000) << std::endl << rand_int (1,1000) << std::endl << rand_int (1,1000) << std::endl; return 0; } ________________________________________ From: chun ping wang [mailto:cablepuff@gmail.com] Sent: Friday, May 19, 2006 3:55 AM To: boost-users(a)lists.boost.org Subject: [Boost-users] Newbie question: Random numbers. I have a simple question, is there a very fast and effecient way to generate random numbers that are fast on the fly. The numbers are really randomize and distorted... /*************************************************** * generates a random number between a and b * * @param a the starting range * * @param b the integer ending range * * @return N such that a <= N <= b * **************************************************/ template <class T> T randint(const T& a, const T& b) { BOOST_STATIC_ASSERT(boost::is_integral<T>::value); assert (b >= a); typedef boost::minstd_rand base_generator_type; typedef boost::uniform_int<> distribution_type; typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type; base_generator_type generator(boost::numeric_cast<unsigned long>(clock())); gen_type ran_gen(generator, distribution_type(a, b)); for (int i = 0; i < 30000; ++i) generator.seed(boost::numeric_cast<unsigned long>(clock())); return ran_gen(); } This works but is super slow... are there effective ways to do it... Thanks.

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[regex] odd partial matching behaviour
by Andrew McDonald 19 May '06

19 May '06

Hi, I suspect I may be about to be hideously embarassed, but for the life of me I cannot see what I have done wrong, so please be kind if this turns out to be my fault ;) A few days ago I was testing a simple regex based log parser I had written and when it failed to correctly extract some of the log data. Log files were typically large so the file was read in blocks and match_partial was used to cope with matching data that was broken over a block boundary. Some poking about revealed that the data in question had been broken over boundary and regex_search had returned no match rather than a partial match, resulting in the initial section of the data being discarded and thus not subsequently matched. I have since spent several hours refining the original regex and data down to the most minimal form that still reproduces the behaviour. Sadly I have run out of time for now so have not yet had a chance to snoop around with the debugger (plus I am not yet familiar with the regex implementation details). I thought I would post anyway in case this was a known problem or an obvious fubar on my part. I am using boost_1_33_1, in Microsoft Visual C++ 2005 Express Edition version 8.0.50727.42. Boost has been built with the vc-8_0 toolset. The regex in question contains non-greedy repeats and the Boost.Regex history page http://www.boost.org/libs/regex/doc/history.html does mention several bug fixes in recent revisions for both non-greedy repeats and partial matches. I am using the latest version mentioned (1.33.1), so I am assuming these are not the cause. Additionally the caveats mentioned on http://www.boost.org/libs/regex/doc/partial_matches.html regarding expressions that always produce partial matches, and expressions that preferentially produce partial matches to full matches, do not seem to apply. A search of the GMane mailing list archive also did not seem to find any posts that were relevant. The regex (default syntax) and test data are: const regex TEST_REGEX("A[^B]*?B.*?C"); const char TEST_DATA[] = "AxBxC"; The program (included below) matches the test string against the regex, removes the last character from the test string and repeats. It produces the following output. Test: AxBxC Result: Full Match Test: AxBx Result: No Match !!!! Test: AxB Result: Partial Match Test: Ax Result: Partial Match Test: A Result: Partial Match Unless I am completely crazy, logic would suggest that it should be impossible to have no match for a string that is one character less than a full match, especially as we then have partial matches for even less input. FYI, I cannot seem reduce the regex further without this behaviour disappearing. All the following (slight) modifications to the problematic regex seem to make the behaviour disappear. // only first non-greedy repeat "A[^B]*?B" // altered first non-greedy repeat "A.*?B.*?C" // removed initial fixed char "[^B]*?B.*?C" // make first repeat greedy "A[^B]*?B.*?C" // make second repeat greedy "A[^B]*?B.*C" Test program ============================================= #include <boost/regex.hpp> #include <string> #include <iostream> using namespace boost; using namespace std; namespace boost { void assertion_failed(char const * expr, char const * function, char const * file, long line) { cout << "Boost assertion failure: (" << expr << ") in " << function << ", " << file << "(" << line << ")" << endl ; } } const regex TEST_REGEX("A[^B]*?B.*?C"); const char TEST_DATA[] = "AxBxC"; const char* END = TEST_DATA + (sizeof(TEST_DATA) - 1); // output test data and type of match void test(const string& data) { cout << "Test: " << data << endl; cout << "Result: "; smatch match; if ( !regex_search(data, match, TEST_REGEX, match_partial) ) { cout << "No Match !!!!" << endl; return; } // check for partial match if (!match[0].matched) { cout << "Partial Match" << endl; return; } cout << "Full Match" << endl; } int main(int argc, char * argv[]) { // start with the full match and // iteratively remove last character // and check regex matches const char* start = TEST_DATA; for(const char* end = END; end != start; --end) { // convert to string just for ease of output test(string(start, end)); } return 0; } ============================================= regards, Andrew McDonald System Architect > Norwood Systems Australia Pty Ltd Level 1, 71 Troy Terrace PO Box 1281 Subiaco, WA 6904 > Tel +61 8 9380 7766 > Fax +61 8 9380 7733 andrew.mcdonald(a)norwoodsystems.com > > The information in this email, and any attachments, may contain confidential information and is intended solely for the attention and use of the named addressee (s). It must not be disclosed to any person(s) without authorization. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorized to, and must not, disclose, copy, distribute, or retain this message or any part of it. If you have received this communication in error, please notify the sender immediately. > > > >

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[function][lambda] compile problem
by Christian Rössel 19 May '06

19 May '06

Dear list, I have a class Manager that wraps an associative container (e.g. std::map) and that provides a method that calls a std::find_if to search on the mapped_type. template <typename Func> boost::optional<Value&> find_if (Func func); I want to pass free functions, functors, boost::function objects or boost::lambda expressions to it. There is no problem with free functions and functors but with boost::function objects (not always) and boost::lambda expressions. The two lines that do not compile are commented in the code below. Please find the entire error messages attached. What am I doing wrong? Thanks and best regards, Christian #include <boost/optional.hpp> #include <boost/utility.hpp> #include <boost/function.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <algorithm> #include <map> #include <utility> template <typename Key, typename Value, template <typename Key, typename Value, typename Compare, typename Alloc> class AssocContainer, typename Compare = std::less<Key>, typename Alloc = std::allocator<std::pair<const Key, Value> > >> class Manager : public boost::noncopyable { public: typedef AssocContainer<Key, Value, Compare, Alloc> AssocCont; typedef Value value_type; Manager (const Compare& compare = Compare (), const Alloc& alloc = Alloc ()) : cont_ (compare, alloc) {} ~Manager () { cont_.clear (); } bool insert (Key key, Value value) { return cont_.insert (std::make_pair(key, value)).second; } template <typename Func> boost::optional<Value&> find_if (Func func) { using boost::lambda::_1; using boost::lambda::bind; typename AssocCont::iterator findResult = std::find_if (cont_.begin (), cont_.end (), bind(func, bind(&AssocCont::value_type::second, _1))); if (findResult != cont_.end()) { return boost::optional<Value&> (findResult->second); } return boost::optional<Value&> (); } private: AssocCont cont_; }; typedef Manager<char, int, std::map> Container; bool find42function (const Container::value_type& value) { return value == 42; } struct Find42functor : public std::unary_function<Container::value_type, bool> { bool operator () (const Container::value_type& value) const { return value == 42; } }; int main () { Container cont; cont.insert ('a', 42); // free function ------------------------------------------------------- cont.find_if (&find42function); boost::function<bool (int)> func_1 (&find42function); cont.find_if (func_1); // Functor ------------------------------------------------------------- cont.find_if (Find42functor()); Find42functor functor; boost::function<bool (int)> func_2 (functor); cont.find_if (func_2); boost::function<bool (int)> func_3 = Find42functor(); cont.find_if (func_3); boost::function<bool (int)> func_4 (Find42functor()); //cont.find_if (func_4); // does not compile /* error message: ======================================================== /d/vendor/include/boost/lambda/detail/function_adaptors.hpp: In static member function `static Result boost::lambda::function_adaptor<Result (*)(Arg1)>::apply(Result (*)(Arg1), A1&) [with RET = boost::function<bool ()(int), std::allocator<void> >, A1 = int, Arg1 = Find42functor (*)(), Result = boost::function<bool ()(int), std::allocator<void> >]': ... test.cpp:50: instantiated from `boost::optional<Value&> Manager<Key, Value, AssocContainer, Compare, Alloc>::find_if(Func) [with Func = boost::function<bool ()(int), std::allocator<void> > (*)(Find42functor (*)()), Key = char, Value = int, AssocContainer = std::map, Compare = std::less<char>, Alloc = std::allocator<std::pair<const char, int> >]' test.cpp:101: instantiated from here /d/vendor/include/boost/lambda/detail/function_adaptors.hpp:218: error: invalid conversion from `int' to `Find42functor (*)()' see error_func_4.txt for the entire error message ========================================================================*/ // lambda -------------------------------------------------------------- using boost::lambda::_1; boost::function<bool (int)> func_5 (_1 == 42); cont.find_if (func_5); //cont.find_if (_1 == 42.0); // does not compile /* error message: ========================================================= /d/vendor/include/boost/lambda/detail/function_adaptors.hpp: In instantiation of `boost::lambda::function_adaptor<bool>::sig<boost::tuples::cons<bool, boost::tuples::cons<int, boost::tuples::null_type> > >': ... test.cpp:50: instantiated from `boost::optional<Value&> Manager<Key, Value, AssocContainer, Compare, Alloc>::find_if(Func) [with Func = boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::relational_action<boost::lambda::equal_action>, boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::placeholder<1> >>, const double, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >, Key = char, Value = int, AssocContainer = std::map, Compare = std::less<char>, Alloc = std::allocator<std::pair<const char, int> >]' test.cpp:117: instantiated from here /d/vendor/include/boost/lambda/detail/function_adaptors.hpp:32: error: `bool' is not a class, struct, or union type ... See error_lambda.txt for the entire error message ========================================================================*/ return 0; }

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program_options (lexical_cast) and QString
by Christoph Duelli 19 May '06

19 May '06

I am trying to parse my options into a QString. I have provided streaming operators for QString, so code like the following does compile QString sProgram; desc.add_options() ("program,p", po::value<QString>(&sProgram), "..."); It does even work if I pass 'simple' options: -p test will work -p "test oops" will not The cause for that seems to be that the lexical_cast<QString>("test oops") (in program_options) fails (it does fail). If I use std::string the above does work. Seems providing streaming ops was not enough. QString s; "a b" >> s; now s=="a" lexical_cast has special support for string/wstring according to its docs. I need something similar for QString... Can anyone point me in the right direction? Can I (and how) make lexical_cast treat QStrings like regular std::strings? Thanks for any help, Christoph

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Newbie question: Random numbers.
by chun ping wang 19 May '06

19 May '06

I have a simple question, is there a very fast and effecient way to generate random numbers that are fast on the fly. The numbers are really randomize and distorted... /*************************************************** * generates a random number between a and b * * @param a the starting range * * @param b the integer ending range * * @return N such that a <= N <= b * **************************************************/ template <class T> T randint(const T& a, const T& b) { BOOST_STATIC_ASSERT(boost::is_integral<T>::value); assert (b >= a); typedef boost::minstd_rand base_generator_type; typedef boost::uniform_int<> distribution_type; typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type; base_generator_type generator(boost::numeric_cast<unsigned long>(clock())); gen_type ran_gen(generator, distribution_type(a, b)); for (int i = 0; i < 30000; ++i) generator.seed(boost::numeric_cast<unsigned long>(clock())); return ran_gen(); } This works but is super slow... are there effective ways to do it... Thanks.

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program_options - ambiguous option
by Santosh Joseph 19 May '06

19 May '06

Code snippet is below...basically I have 2 options I want to process "host,s" & "help,h". I would like to process options like this: for host: --host, -host, -s for help: --help, -help, -h Maybe I setup the opt_style variable wrong or is this correct behavior? I'm using boost 1.33.1 when i run the program: > po.exe -host localhost -h *** Command line processing error: ambiguous option h thanks for any help, -Santosh ====================================================== #include <iostream> #include <string> #include "boost/program_options.hpp" using namespace std; namespace po = boost::program_options; int main(int, char *[]) { po::variables_map vm; po::options_description desc("Options"); try { string strHostname; desc.add_options() ("host,s", po::value<string>(&strHostname), "") ("help,h", "Show this help message"); po::options_description cmdline_options; cmdline_options.add(desc); int opt_style = (po::command_line_style::unix_style | po::command_line_style::allow_long_disguise | po::command_line_style::allow_slash_for_short); po::store(po::parse_command_line(argc, argv, cmdline_options, opt_style), vm); po::notify(vm); cout << "host: " << strHostname << endl; if( vm.count("help") ) cout << "help is true" << endl; } catch(exception &e) { cout << endl << "*** Command line processing error: " << e.what() << endl; } return 0; } __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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