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

[units] Basic usage questions
by Bryce L Nordgren 29 Jul '10

29 Jul '10

Q1 ============================================================================= What are the rules about what is allowed where? Or perhaps more appropriately, why are the rules so strange? I've been playing with units in boost 1.43.0 using gcc 4.4.3/mingw on win xp and I think I've deduced what is allowed. For instance, when declaring variables, you can do: quantity<si::length> l(1.0*si::meters) ; quantity<si::meter_base_unit::unit_type> l(1.0*si::meters) ; quantity<us::yard_base_unit::unit_type> l(1.0*si::meters) ; but not quantity<si::length> l(si::meters) ; (missing the scalar in front of the units) or quantity<si::meters> l(1.0*si::meters) ; (si::meters is not quantity-variable-declaration material??!?) Q2 ============================================================================= I spent a long time looking for a way to construct a variable with on-the-fly defined units, in order to store interim quantities which may have strange units when implementing the computation of a long expression. This would also be useful to precompute some terms which occur more than once, but which don't necessarily represent any kind of sensible value that you would return as a final result. I wanted to do something like this: quantity<si::length / si::mass> dummy_var_1 = (some_interim_expression reducing to si::length/si::mass) but I can't figure out how to do it. For the moment, I plan on just using the vast array of predefined units on the derived dimensions. However, it would be nice to be able to divide up the computation in whatever way seems natural given the equation, even if the interim variables don't represent rational physical quantities. Q3 =============================================================================== And I suppose my last question is "What does a unit system buy you?", meaning that since "yards" is not part of a unit system and I can declare a variable of type quantity<us::yard_base_unit::unit_type>, what is the added benefit of constructing a unit system which contains yards? Don't misinterpret this as a string of complaints. :) I am very grateful to not have to write this myself. I'm just having some trouble understanding how to apply the library to my situation. ;) Thanks, Bryce

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[Serialization] Serialize base and derived classes.
by BlueAngel 29 Jul '10

29 Jul '10

Hi lists, I'm working with the Serialization library but I'm having some troubles with it. The tutorials in the website shown me much but still I need help. I'm using XML archives. I have this classes actually (these classes are all builders/prototypes, they serialize the datas and then they should make a new object with those datas): Serializer (an interface, every class which need serialization must be derived from this, however this is only a marker, it will be not serialized) RenderableSerializer : public Serializer - this isn't pure virtual however shouldn't be never serialized directly (since the object made by this class is a pure virtual one) - These will use the tag <renderable> SkyboxSerializer : public RenderableSerializer - these will use the tag <skybox> EntitySerializer : public Serializer - these will use the tag <entity> many other classes will be added in future and they'll all derive form RenderableSerializer. Now the problem is EntitySerializer have a pointer to a RenderableSerializer and when I serialize EntitySerializer the pointer to that class is considered to be a RenderableSerializer and not the derived class. I don't know at priori which class is the base class and this lead to problem. If I serialize a SkyboxSerializer I have the correct tag: a <skybox> which have inside a <renderable> and the datas are correct. If I try to serialize an Entity I had a lot of problem, mostly just make the library crash. As I've seen in the tutorial I should register all the derived classes before pass the pointer to the Archive. I did it registering the SkyboxSerializer classes but it lead to a wrong xml: a correct <entity> tag which have a correct <skybox> with all it's data but also a wrong <renderable> tag which have inside the same data of the tag <skybox> instead of the data of a RenderableSerializer class. Now the question is: is there a correct way to use the library this way? With a pointer to a base class of which the derived is not known? My code is too big and I made many attempt to use the library so I'm not posting it in this message. If you need it I will post it. Thank you for your replies.

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suspend an asio operation
by Lloyd 29 Jul '10

29 Jul '10

Hi, I am using asio for a network server. Based on the client request the server performs the operation. Some operation could take a very long time. so we would like to implement a "feature" to terminate the long process from client side by sending some other command. Is there any mechanism in "ASIO" to do this? Thanks, Lloyd ______________________________________ Scanned and protected by Email scanner

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[wave] problem with "/##/" macro
by Evgeniy Rigkov 29 Jul '10

29 Jul '10

Hello, I found a problem with preprocessing "/##/" macro. For example, I have a next code: #define COMMENT_MACRO /##/ void test() { COMMENT_MACRO comment } This code can pe preprocessed (with help any correct preprocessor) to next: void test() { // comment } But after usage boost::wave utility (from boost 1.43) I have this code: void test() { comment } How you see the symbol "//" is forgotten. How fix it?

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[asio] Newbie problem running tutorial example Daytime.4 - Asynchronous UDP daytime client
by Adolfo Jimenez 29 Jul '10

29 Jul '10

Hi list: Using MSVCPP C++ 9.0 and Boost_1_43_0, and trying to follow the examples in the tutorial. The Daytime.4 example hangs in line size_t len = socket.receive_from(boost::asio::buffer(recv_buf), sender_endpoint); it seem that wait indefinitely for a response. Using this server: char* serverName = "ntp-nist.ldsbc.edu"; // 198.60.73.8 LDSBC, Salt Lake City, Utah Neither with: char* serverName = "time-nw.nist.gov" or any other in the http://tf.nist.gov/tf-cgi/servers.cgi# list. By the way, the Daytime.1 (asynchronous TCP datytime client) example and Timer1 to 5 examples works fine for me. Any suggestion would be appreciated. Thanks A.J.Millan

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[datetime] Stability of ptime string representation
by Rush Manbert 28 Jul '10

28 Jul '10

I have an application that uses the string representation of a ptime object in a way that requires that representation to be stable across many years and across multiple releases of the DateTime library. We started out using the to_iso_extended_string() method to generate the string representation. I am worried that the periodic addition of leap seconds could mess me up. The scenario is rather complicated: Let's say that I go into production tomorrow using Boost 1.42. All is well. The Powers That Be decide that there will be a leap second added at the end of 2010. We keep using 1.42. A year from now I record a time value. If I did it exactly one year from when I'm writing this, the to_iso_extended_string() representation would be: 2011-07-28T10:59:30.532000 In 2012, we change out our Boost libraries for version 1.50, which contains a new version of the DateTime library which I assume knows about the leap second that was added at the end of 2010. Here's what I'm worrying about: If, sometime in 2012 after we switch libraries, I retrieve the ptime value that I recorded in 2011 by calling to_iso_extended_string(), will I get the same string that I was getting in 2011 when I was running on a pre-leap-second-addition version of DateTime, or will it be different by a second? Thanks, Rush

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[type traits][enable_if] how do I resolve ambiguous class template instantiation?
by Steve Lorimer 28 Jul '10

28 Jul '10

I'm trying to use template specialization and enable_if / type_traits to correctly allocate memory for different types, where the template parameter will be one of: 1. boost::intrusive_ptr // create U on the heap, return intrusive_ptr 2. boost::shared_ptr // create U on the heap, return shared_ptr 3. U* // create U on the heap, return raw pointer 4. U // create U on the stack I'm pretty sure I'm just doing something stupid, but I'm getting ambiguous conflicts between my template for types of U and the smart pointer types. Please can you comment on how to fix the code below? TIA Steve #include <boost/utility.hpp> #include <boost/type_traits.hpp> #include <boost/intrusive_ptr.hpp> #include <boost/shared_ptr.hpp> #include <iostream> template<typename U, class Enable = void> struct alloc; template<typename U> struct alloc<U, typename boost::disable_if< boost::is_pointer >::type > { U operator()() { std::cout << __LINE__ << std::endl; return U(); } }; //----------------------------------------------------- template<typename U> struct alloc<U, typename boost::enable_if< boost::is_pointer >::type > { U operator()() { std::cout << __LINE__ << std::endl; return new U; } }; //----------------------------------------------------- template< typename U > struct alloc< boost::intrusive_ptr > { boost::intrusive_ptr operator()() { std::cout << __LINE__ << std::endl; return boost::intrusive_ptr(new U); } }; //----------------------------------------------------- template<typename U > struct alloc< boost::shared_ptr > { boost::shared_ptr operator()() { std::cout << __LINE__ << std::endl; return boost::shared_ptr(new U); } }; //----------------------------------------------------- template<typename T> struct test { alloc<T> create; T fun() { return create(); } }; struct foo { uint32_t refs; foo() : refs() { std::cout << "foo" << std::endl; } }; inline void intrusive_ptr_add_ref(foo* p) { ++p->refs; } inline void intrusive_ptr_release(foo* p) { if (!--p->refs) delete p; } int main() { test<int*> a; int* p = a.fun(); *p = 5; test<int> b; int d = b.fun(); d = 5; test< boost::intrusive_ptr<foo> > c; boost::intrusive_ptr<foo> z = c.fun(); z.get(); test< boost::shared_ptr<int> > gd; boost::shared_ptr<int> x = gd.fun(); x.get(); return 0; }

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does Boost Parameter support non-type class template parameters?
by Nathan Ridge 28 Jul '10

28 Jul '10

Hello, Does the Boost Parameter library's named template parameters feature work for templates where some of the parameters are non-type parameters? Thanks, Nate. _________________________________________________________________ MSN Dating: Find someone special. Start now. http://go.microsoft.com/?linkid=9734384

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how to release element from ptr_map?
by archie14 28 Jul '10

28 Jul '10

I have an instance of ptr_map<int, classA>. I need to release an element from the map and use it somewhere else, making sure that it will not be deleted when the instance of ptr_map is deleted. I am successfully doing it with ptr_vectors, but can't get it right with ptr_map. What is the proper syntax of such call? I am doing it like in the code below, which does not compile. class classA {}; typedef ptr_map<int, classA> ptrmaptype; ptrmaptype val; val.insert(1, new classA()); ptrmaptype::mapped_type t = val.release (val.begin()); // I want "t" to be of classA* type

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[Random] Getting normal_distribution<> to work
by Hossein Haeri 28 Jul '10

28 Jul '10

Dear all, When I run the following simple code, the output is "-1.#IND" in MSVC 2008 and "nan" in GCC 4.4.0. I guess that means something is not initialised yet... So, what's missing here? boost::normal_distribution<double> gen; boost::mt19937 engine; double r = gen(engine); cout << r; TIA, --Hossein

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