May 2006 - Boost-users - lists.preview.boost.org

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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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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