December 2004 - Boost-users

[Review Results] Named Parameters Library
by Doug Gregor 06 Dec '04

06 Dec '04

The Named Parameters Library has been accepted into Boost. Congratulations to the authors, David Abrahams and Daniel Wallin. The vast majority of reviews were positive, although most reviewers requested additional documentation. Here is a list of the most important/commonly-requested changes or additions to the library: - More documentation! Specifically, + Automatic overload generation should go into the tutorial + Document operator, + Performance data (what's the cost?) + Reference section + "Best practices" section. - Add a metafunction for getting the type of a parameter, e.g., param_type<Params, width_t>::type. - Add test cases for the automatic overload generation macros. - Fix the BOOST_NAMED_PARAMS_MAX_ARITY bug; Cromwell Enage provided a solution. Doug Gregor Review Manager

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Q: Stopping threads (Win32) or... the mysterious case of the thread with split personality
by Dan Dimerman 06 Dec '04

06 Dec '04

Hello, I would like to ask the group if you know of an efficient and clean way to stop a thread. What I've been using till now was a while loop in the function operator()() given to the boost::thread when created, whose condition was a boolean data member. This boolean was the means to stop the thread, such that when it was turned off, the child thread would exit the while loop and join the main thread. I am seeing now that this data member is being held twice (one copy for the main thread and one copy for the child thread) and there's no synch between the two copies; so when the main thread turns it off / false, the child thread goes on (since its copy is still on / true) and hell breaks loose. I am using VC7 in debug mode, so I started looking for some kind of flag/optimization I might be inadvertently using that makes data members into registers (thus explaining the copies), but couldn't find anything of the sort. Any help will be greatly appreciated... Dan --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com) Version: 6.0.805 / Virus Database: 547 - Release Date: 03-Dec-04

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determining a sensible result type for a function
by Agoston Bejo 06 Dec '04

06 Dec '04

Hi! Let's consider this function object: template<typename TLeft, typename TRight> struct mixed_plus : public binary_function<TLeft, TRight, TLeft> { result_type operator() (first_argument_type left, second_argument_type right) const { return left + right; } };

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get_wider<int, float> == float - what is it called in boost?
by Agoston Bejo 06 Dec '04

06 Dec '04

Hi! I may have posted the first half of this question once, sorry for that! : ) The question in short: which boost library enables me to get the "wider" datatype of two, such that get_wider<int, float>::type will be float, and get_wider<float, int>::type will also be float. Hopefully get_wider<int, string>::type will generate a compile-time error, since the two are not convertible to each other. More verbosely: Let's take a look at this simple functor class: template<typename TLeft, typename TRight> struct mixed_plus : public binary_function<TLeft, TRight, TLeft> // result_type: bad solution! { result_type operator() (first_argument_type left, second_argument_type right) const { return left + right; } }; All is fine if I write this: cout << mixed_plus<float, int>()(5.5, 5) << endl; OUTPUT: 11.5 (as expected) But when I write this: cout << mixed_plus<int, float>()(5, 5.5) << endl; OUTPUT: 10 (as expected but not as intended) I vaguely remember that there is a boost library that is able to generate the "wider" data type of two data type, with the help of which I would be able to have the result_type typedef always the appropriate one.

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lu.hpp : permutation matrix error
by Daniel L Elliott 06 Dec '04

06 Dec '04

Hello, I am completely stumped. Using the cvs head 1.32 version of boost with the following program: #include<lu.hpp> #include<vector.hpp> #include<io.hpp> #include<iostream> using std::cout; using std::endl; using namespace boost::numeric::ublas; int main(){ // create a permutation matrix permutation_matrix<size_t> P( size ); // default contructions gives the identity-permutation cout << P << endl; return 0; } I get the following errors: g++ -c -I. -I/s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas -Wall -g3 -I. -I/s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas -o permutationTest.o permutationTest.cpp In file included from permutationTest.cpp:1: /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:24: error: parse error before `,' token /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: error: ` vector_type' is not a class or namespace /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: error: ` size_type' is not a class or namespace /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: error: ` vector_type' fails to be a typedef or built in type /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: error: ISO C++ forbids declaration of `size_type' with no type /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: error: template declaration of `typedef int boost::numeric::ublas::size_type' /s/chopin/a/grad/dane/thesis/code/boost-1.32/include/boost-1_32/boost/numeric/ublas/lu.hpp:29: confused by earlier errors, bailing out Any ideas as to what might be wrong here? Thank you. -- dan elliott ************************** Dan Elliott 402-210-6429 (me) or 402-210-6735 (amy) dan_elliott(a)cox.net **************************

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HowTo Iterator Facade
by Duane Murphy 06 Dec '04

06 Dec '04

I am implementing an iterator via iterator facade. The container that the iterator is being used with can only return dereferenced values by value (not by reference). If I implement the dereference() function (for facade) by returning a value (instead of reference) then it appears that the iterator works properly. The most important operation that does _not_ work is that the iterator cannot be used with bind(). (bind cannot be used with non-const return types.) If I change the iterator to return a reference type then the iterator functions still work and so does bind. What is the proper way of implementing an iterator with this limitation so that it works properly with bind? In the past, I keep a mutable value member along with the iterator to store the last dereferenced value. Of course this is fraught with problems. Is there an example iterator that demonstrates the proper way of doing this? Is there some kind of proxy class that can be used to overcome this limitation? Thanks for your help, ...Duane

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boost filesystem path question
by Surya Kiran Gullapalli 05 Dec '04

05 Dec '04

Hi, I've this code, which is supposed to work on both windows and linux OS. I'll get a particular directory/file path from a fileselection dialog, where by i process this path. The question for me, is I'm using the boost::filesystem::path constructor like this. boost::filesystem::path p (path_from_fs_dialog, boost::filesystem::native) ; Its working fine on linux (as the string path_from_fs_dialog contains "/" as directory separator). when comes to windows path_from_fs_dialog contains "\" as the directory separator, and the path constructor is throwing exception. What could have been the reason? I've to change the namecheck function from "native" to "no_check" Any ideas what might have gone wrong? Thanks in advance, Surya

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Pool allocating
by Jean-Eric Cuendet 05 Dec '04

05 Dec '04

Hi, I need the following for our Linux C++ soft: - Create a HeapSpace of FixedSize (say 1Mb) - Allocate FixedSize piece of memory (always alloc 16 bytes from this heap for ex.) - Return NULL if no more space in the HeapSpace - Delete them. - Release the memory when all pieces are deleted Is there a way to do exactly that with Boost? Thanks. -jec

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Re: Newbie using regex libraries (John Maddock)
by Mark Helzer 05 Dec '04

05 Dec '04

----------------------------- Message: 3 Date: Fri, 3 Dec 2004 10:57:05 -0000 From: "John Maddock" <john(a)johnmaddock.co.uk> Subject: Re: [Boost-users] Newbie using regex libraries To: <boost-users(a)lists.boost.org> Message-ID: <01c301c4d927$1a2b6520$03800252@fuji> Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original > In developing a very simple test, I ran into an issue with the library. > I linked with libboost_regex-gcc.so and ran into a relocation run time > error -- undefined symbol: __dso_handle. > > I found the symbol in libboost_regex-gcc-mt-d-1_31.so.1.31.0. I linked > with that and my test works. > > So, it seems odd that I would not use one of the more generic library > names (ending in .so). Is this perhaps a configuration issue on my > part? Those two libs should be the same thing, in fact I think one should be a link to the other shouldn't it? No, they are not. Although that is what I would have expected... -rwxr-xr-x 1 eoapi clients 4976367 Apr 22 2004 libboost_regex-gcc-mt-d-1_31.so.1.31.0 -rwxr-xr-x 1 root root 629005 Jun 29 06:16 libboost_regex-gcc.so I shall clean it up and try rebuilding John.

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Problems serializing via pointers
by Jeffrey Holle 04 Dec '04

04 Dec '04

At this point, the last compilation problem in applying the boost.serialization library to my application has to do with pointers. Specifically, its pointers to std::string and char member attributes. I have other pointer member attributes that compile successfully, but this point to objects that have serialize methods. I have attempted use of register_type and am including "serialization/string.hpp" in the modules that have pointer to string attributes. These actions were not affective. As an example of the type of compilation error, when I uncomment the following attribute's archive attempt: char *m_pByPointerPrefix; I get: /home/jholle/boost_1_32_0/boost/serialization/access.hpp: In static member function `static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = char]': /home/jholle/boost_1_32_0/boost/serialization/serialization.hpp:78: instantiated from `void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = char]' /home/jholle/boost_1_32_0/boost/serialization/serialization.hpp:121: instantiated from `void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::binary_iarchive, T = char]' /home/jholle/boost_1_32_0/boost/archive/detail/iserializer.hpp:155: instantiated from `void boost::archive::detail::iserializer<Archive, T>::load_object_data(boost::archive::detail::basic_iarchive&, void*, unsigned int) const [with Archive = boost::archive::binary_iarchive, T = char]' VariableName.cpp:102: instantiated from here /home/jholle/boost_1_32_0/boost/serialization/access.hpp:106: error: request for member `serialize' in `t', which is of non-class type `char' What is the solution to this?

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