- Boost-users - lists.boost.org

Re: [Boost-users] Newbie question: Random numbers.
by james.jones＠firstinvestors.com 22 May '06

22 May '06

From: Rene Rivera <grafik.list(a)redshift-software.com> > A cheap method, that I've used, is to hook up a radio to your audio card > and record a frequency which is sufficiently far away from real radio > traffic. With some post processing, to clean up and to ensure crypto > safe entropy levels, it works very well and gives gigs of entropy data > quickly. Just to play devil's advocate for a minute, wouldn't that make the frequency basically the crypto key that would need to be protected? If a potential attacker knew the frequency, he could broadcast a low-entropy signal on it, causing your previously-random seeds to become nonrandom and ruining your crypto. - James Jones Administrative Data Mgmt. Webmaster 375 Raritan Center Pkwy, Suite A Data Architect Edison, NJ 08837

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connect boost::signals inside of a slot
by Setzer, Sebastian (ext) 22 May '06

22 May '06

Hi, If you connect (disconnect) a new slot to a signal inside of a slot of the same signal, what happens? - are the slots called which where connected before the signal was called, - or is new slot be called this time, too, - or is the behaviour undefined? I didn't find anything on this subject in the manuals. Even if the behaviour is undefined, that should be mentioned. Sebastian Setzer

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[regex] "Invalid content of repeat range" when using greediness and capture operators?
by Christopher Hart 22 May '06

22 May '06

I've run into a problem where I'm getting an "Invalid content of repeat range" when attempting to match a string using greediness and capture operators. I'm using the following function (basically taken from the "print captures" example in the regex docs): void find_matches(const std::string& regx, const std::string& text) { boost::regex e(regx, boost::regex::perl); boost::smatch what; std::cout << "Expression: \"" << regx << "\"\n"; std::cout << "Text: \"" << text << "\"\n"; if(boost::regex_match(text, what, e)) //, boost::match_extra)) { ... [snip] ... } else { ... } } ... invoked by: find_matches(html, "<p class=\"priceBest\"><a href=(.*?)>"); The pattern I'm trying to match is working in Perl program (e.g. if ($html =~ m|<p class="priceBest"><a href=(.*?)>|gs) {...} ), so it seems like the pattern should be syntactically correct. I'm building on Mac OS X 10.4 (Intel) with Boost 1.33.1. I'm new to Boost and probably spoiled by Perl pattern matching, so I'm guessing I'm missing something simple. Any help or suggestions are appreciated! Thanks, Chris Hart

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[statechart] Event handlers and state reusage
by Johan Nilsson 22 May '06

22 May '06

Hi, couple of quick questions: 1. For a state, is it possible to specify a method that will be called when an event with no defined handlers is received? 2. Is is somehow possible to reuse state definitions as substates of different "higher-level" states? Sorry about the terminology, I'll give a specific example: - I've got an application that can be either in remote or locally controlled mode (this is the highest-level states). - Certain events are allowed both in remote and local, while some are not. As an example, the "CommandEvent" event should be handled both in remote and local - resulting in the "ExecutingCommandState" being entered. - I'd like to be able to reuse the definition of ExecutingCommandState regardless of the enclosing state being Remote or Local - Possible? // Johan

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valarray and serialization
by Thomas DAVID 21 May '06

21 May '06

Hi all, I'm a new user of Boost and I'm in trouble with the serialization of a valarray of float. It seems that Boost doesn't deal with this type, and I found no information in /usr/include and no more on google, except this discussion (http://lists.boost.org/Archives/boost/2005/10/95295.php) and it didn't give me valuable information on my problem. So, my questions are : 1) Is Boost able to serialize directly a valarray ? (and how) 2) Otherwise, do I need to code the store and load function and how (I'm not sure to be good enough to do it properly and I'm quite sure that somebody faced this problem before me) Any help/clue would be appreciated Thomas DAVID

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[serialization] bpos_ptr NULL in basic_oarchive_impl::save_pointer
by Hugh Hoover 21 May '06

21 May '06

I'm currently using 1_33_1 I've been having some problems with serialization so I built a test module that serializes a set of class template instantiations in a way that vaguely matches my real application. The template instances are derived classes from a common pure virtual base class. I got it to work properly in the test app, but then noticed I hadn't done BOOST_IS_ABSTRACT or BOOST_CLASS_EXPORT for the template instantiations like I had in my real classes. When I add BOOST_IS_ABSTRACT for the derived template instantiations, it compiles, but then crashes in save_pointer because bpos_ptr is NULL. The initial failure is higher in the call stack at boost::archive::detail::save_pointer_type<>::invoke (oserializer.hpp), where it requests the bpos_ptr from register_type. I realize NOW that it's probably performing as expected (except there's no assert) since the derived class is NOT abstract. I had run into problems (much) earlier where it appeared that I needed the BOOST_IS_ABSTRACT on the derived classes and not the base class but that may have been a side effect of other things I was doing wrong. It had not appeared to be a problem using the superfluous BOOST_IS_ABSTRACT until recently (switch to 1_33_1?). I note that the boost cvs tip version (for 1_34) also does not have an assert there. I'm not sure if that would have helped me figure out what was wrong, but at least an assert would terminate things closer to the source of the problem... Anyway - perhaps this will help someone else who's running into the NULL bpos_ptr problem... Thanks for your great work and support on the forum here! Hugh Hoover Enumclaw Software.

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[serialization] Serializing classes with no default constructors
by Catalin Pitis 20 May '06

20 May '06

Hi I wonder how can a class that doesn't provide a default constructor can be serialized? As far as I saw, the serialization methods assume that the object is already created. This makes me nervous :), because I wouldn't create an object that is not in a valid state after creation... Am I missing something in this library? Can I do it "the easy way"? Thanks Catalin

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function returns T*, I want to put that into a shared_ptr
by Josh S 20 May '06

20 May '06

I have a few newb questions: I have the following classes class Base { Base(); virtual ~Base(); virtual doStuff(); } class Foo: public Base { doStuff(); } class FooContainer { createFoos(int numOfFoos); Foo* getFoo(int indexToFoo); Destroy(); } class BaseContainer { void addObj(boost::shared_ptr<Base> obj); } How do I cast the pointer returned from FooContainer::getFoo(), as something I can pass to BaseContainer::addObj ? Is this correct to do this? Assuming I cant change the implementation of FooContainer or the BaseContainer interface. The BaseContainer interface should not have a special case for adding Foo's. Good practise tells me I shouldn't create a temporary either. I do not want the shared_ptr in BaseContainer to call delete on Foo (I will manually call FooContainer::Destroy() ---- Now, what happens if I instead want FooContainer to only be responsible for creating the Foo objects, and not be responsible for deleting them. Instead I want the shared_ptr to call delete when the objects reference count reaches 0. How would that done? Thanks in advance, Josh S

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Boost vector problem
by zhao haifang 20 May '06

20 May '06

Hey, guys, I want to do vector (has 3 elements in itf) cross product using boost, for example I have vector v1, and v2 and I want to compute v3= v1 X v2, so that v3 is a new vector and be normal to the plane compised of v1 and v2. Does any body has any idea about which function in boost should I call ? Thanks in advance! Helen --------------------------------- Be a chatter box. Enjoy free PC-to-PC calls with Yahoo! Messenger with Voice.

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

19 May '06

I was just checking over my suggestion and realized that clock() is not a good choice for seeding the generator, especially with my optimization. It returns the amount of time since the process started, which in a static initializer for a global variable, will provide very low entropy. In a few test runs, it even returned 0, which caused an assertion failure in the random number library. An ideal solution would be to use random_device, which is defined in boost/nondet_random.hpp. You could then replace the definition of generator with something like this: //Declare the generator as a global variable for easy reuse random_device nondet_generator; base_generator_type generator(nondet_generator()); If random_device isn't implemented on your platform, then you can look into other ways to seed the generator. On my system (Windows XP running VC8) I used GetTickCount(), which returns the number of milliseconds since Windows started. As a last resort, you could call clock() after the user has entered something, either the normal data entry for your program (preferred), or a special request to hit enter. Does anybody else know of other good sources of entropy to seed the generator? I also found that the loop to seed the generator (initialize() in my version) doesn't really help, since the seed function completely replaces the current value of the generator; it doesn't combine with the previous value. > -----Original Message----- > From: Andrew Holden > Sent: Friday, May 19, 2006 9:18 AM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] Newbie question: Random numbers. > > 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. > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users

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