- Boost-users - lists.boost.org

Re: [Boost-users] How to add a type to is_arithmetic
by Chad Walters 16 Oct '07

16 Oct '07

It's not entirely clear from your description if you really need to have is_arithmetic be true for your fixed_point class or if you just want to have some predicate that is true for both the built-in arithmetic types and your fixed_point class. If the former, then you will likely run afoul of problems, for the reasons previously pointed out. Hopefully it is the latter - in which case you should just define your own predicate with the appropriate logic (true for fixed_point or is_arithmetic types). Chad

3 3

Retrieve number os affected rows
by Hamilton Vera 16 Oct '07

16 Oct '07

How to retrieve the number of affected rows after an update? ( I am testing in a MySQL database) I only found this in the list; http://lists.boost.org/Archives/boost/2006/12/114037.php But I was unable to find the sql.rowsaffected() fuction. I am using soci version 2.2.0. -- Hamilton Vera int Administrator (char Network[],char ComputationalSystems[]); Seven Internet http://lib.seven.com.br "Google is my shepherd, no want shall I know"

1 0

[xpressive] crash...
by Ovanes Markarian 16 Oct '07

16 Oct '07

Hello Eric, this code fragment will crash, since 'what' uses iterators into the invalid string x::smatch what; if(x::regex_match(std::string(" (some_type_ptr) xyz,"), what, regex)) //string goes out of scope after this sentance { std::cout << what[0] << endl; // boom! string iterators are no longer valid std::cout << what[1] << endl; } May be there is a way to probit this kind of behaviour during the compilation or at least this can be stated in the docs... With Kind Regards, Ovanes

2 3

[system] in multi-threaded context
by Jeroen van der Wulp 16 Oct '07

16 Oct '07

Hello, I have some problems with the latest changes to asio, which turn out to be caused by problems with boost::system. The newer versions of boost::asio now use boost::error_code provided by boost::system for error handling. On OS X 10.4 with XCode 2.4.1 comparing two boost::error_code objects e1 & e2 always returns false. I believe this is caused by comparing objects accross threads. But this is just a guess. A problem I noticed on with Apple's version of gcc is that static instance variables behave strange, there seems to be a copy for each variable in each compilation unit that uses them? This may also somehow be the cause for my problems with boost::system. Another problem is that when I receive an error_code object, say e, from asio, trying to print e.message() fails with an access violation. This happens on Windows, Linux, OS X. What am I doing wrong? Thanks, Jeroen van der Wulp

1 0

[boost-users] enable_if and checking if class derives from boost::operators does not work.
by chun ping wang 16 Oct '07

16 Oct '07

namespace boost { template <class T, class U> char (& is_op_test(boost::operators<T,U> const&) )[2]; template <class T> char is_op_test(T const&); template<class T> T const& make(); template <class T> struct is_operators : boost::mpl::bool_<(sizeof(is_op_test(make<T>())) == 2)> {}; } and this function declaration. template <typename T, template <typename ELEM, typename = std::allocator<ELEM> > class CONT > typename boost::enable_if<boost::mpl::or_<boost::is_integral<T>, boost:: is_operators<T> >, CONT<T> >::type primelist(const T& MAX_BOUND, const T& K, boost::function<bool(const T&, const T&)> f); BigInteger class declaration looks like this.. class BigInteger : public BigUnsigned, boost::operators<BigInteger>, boost::operators<BigInteger, int> { }; I compile with T = int and it works. When i compile with T = BigInteger I get the following errors. on visual c++. error C2770: invalid explicit template argument(s) for 'boost::enable_if<boost::mpl::or_<boost::is_integral<T>,boost::is_operators<T> >,CONT<T>>::type primelist(const T &,const T &,boost::function<bool(const T &,const T &)>)' ./cs512/c++/primeMain.cpp(24) : see declaration of 'primelist'" on mingw dev-cpp i get this error. unable to find function.... In both cases passing BigInteger does not work. thanks for the help. BigInteger does derive from boost::operators and theirs two overload.

2 2

[filesystem] vacpp errors building 1_34_1 filesystem library on AIX
by Marty Fried 15 Oct '07

15 Oct '07

I've built all the boost libraries on Windows and Red Hat, but there are compiler errors building on AIX using Visual Age (xlC) for the filesystem library. It builds using gcc, but not vacpp, which is the AIX standard compiler. We are using the latest version, V. 8. There is more than one error, but I think they are all similar. I believe that the code envolved is not fully standard compliant. For example, in operations.hpp, there is an error on line 732, col 72; the full error is (I tried to wrap as best I could): The declaration of "end_itr" uses the undefined class "boost::filesystem:: basic_directory_iterator<boost::filesystem::basic_path <std::basic_string<char,std::char_traits<char>,std::allocator<char> >, boost::filesystem::path_traits> >" when the class must be complete. The code is called by line 730, called by 473, called by 689. The problem, I think, is that basic_directory_iterator is not defined until line 822, after all these calls. A coworker created a simple test that reproduced this error, fed it into an online ANSI/ISO C++ Standard test utility by Comeau computing, and it flagged it as an error. Has anyone compiled 1_34_1 using xlC/vacpp? If you need more information, or need the other errors, let me know. -- Marty Fried Left Coast, USA

1 0

boost-build-2.0-m11 and gcc-4.2.2
by Michael Albert 15 Oct '07

15 Oct '07

Greetings. If in "jam_src" I attempt to compile with gcc-4.2.2, the "bjam" executable compiles (using ./build.sh), but "bjam --version" fails on a segmentation fault. I can compile with gcc 3.4.6. Any thoughts? Anyone else seen this behavior? Thanks! -Mike

3 2

[ Boost-users] [preprocessor] - introduce mpl { ... } like asm { ... }
by Frank Bergemann 15 Oct '07

15 Oct '07

Hi, i posted this to comp.lang.c++.moderated: ------------------------------------------------------- Hi, i am just starting to work with "C++ Template Metaprogramming" - using the book of David Abrahams & Aleksey Gurtovoy. And you know, there are things like mpl::plus<> for some operator, mpl::if_<> for a control-struct, mpl:insert<>, mpl:erase<>, mpl:clear<> for STL container like operations, etc. Lots of things re-modeled the "unaccustomed template-syntax" - way for types, which are there in C/C++ language definition already for operating on variables and values. So i wonder if it would be a good option to introduce some mpl { ... } in remembrance of asm { ... } This time not for going down to the assembler level, but going up to the meta level. But with the goal to drop the template fashioned syntax for meta programming by a syntax already familiar in C/C++ language without templates (if this is possible - i don't now enough about that). Well, this is just a gut feeling, that there might be a chance this way to more align "standard" programming with "meta" programming, which then might enable to easier catch the the gray area of borderline between compilation and runtime execution and how to shift that back and forth. What do you think? rgds! Frank ------------------------------------------------------- Then i was thinking, that instead of extending the C++ language, it might be sufficient to use an own preprocessor before handing over to g++ (e.g.). For this maybe using boost::spirit? Finally i was remembering, that there is already some 'preprocessor' project in boost itself. But having a 1st look at it, it doesn't seem to do what i'd like to have. Just as an example - see this extract from boost::enable_if documentation: template <class T> typename enable_if_c<boost::is_arithmetic<T>::value, T>::type foo(T t) { return t; } I'd like to make it s.th. like: mpl { template <class T> if (is_arithmetic(T)) { T foo (T t) { return t;} } } This is just a simple example. But just imagine use of mpl metafunctions like mpl::and_ mpl::or_, mpl::plus, mpl::minus, mpl::equal_to, mpl::less, etc, that could come back to the "natural" &&, ||, +, -, ==, <, etc. [ hmm, i think, i mixed up mpl::enable_if with mpl::if_ - so my example is not correct - but i hope you get my point here ] Them maybe it would also be possible somehow: mpl { template <class T> if (is_arithmetic(T)) { T foo (T t) { return t;} } else { #error "instantiation of foo() not supported for given type T" } } ... to generate usefulcompiler warning/errors. The main point for me is to get find an equivalent to the "strange" template syntax that is more C/C++ alike way to deal with variables and values. Not because template syntax is "strange". But in order to re-align again. rgds! Frank

3 2

[mpl][fusion] making a heterogeneous collection of classes from a list of types.
by Michael Marcin 15 Oct '07

15 Oct '07

Hello, I have the MPL book and I've used some metaprogramming before but I'm always at the edge of my understanding of the language when I do it. I have a problem right now which I suspect is trivial but I can't for the life of me figure out how to do it. I have a list of 25 resource types (class Sound, class Script, etc.) and since they are not mutable I want to share them so I have a resource cache template that looks something like: template< typename Resource > class Cache { public: typedef typename Tag<Resource>::type resource_tag; /// Retrieve a resource by id /// Throws cache_error if the resource couldn't be found in the Repository Resource& Retrieve( ResourceId id ) { // is the resource in the cache? typename ResourceMap::iterator it = m_resources.find( id ); if( it != m_resources.end() ) { return it->second; } else { return LoadResource( id ); } } /// Clears the cache and destructs all cached resources. void Clear() { m_resources.clear(); } private: Resource& LoadResource( ResourceId id ) { Stream stream( Repository::Instance().Retrieve( id, resource_tag::type::value ) ); if( !stream.fail() ) { Resource* res = new Resource(stream); m_resources.insert( id, res ); return *res; } else { throw cache_error( id, resource_tag::type::value ); } } typedef boost::ptr_map< ResourceId, Resource > ResourceMap; ResourceMap m_resources; }; I have a class which must contain a Cache for each of the 25 resource types and support calls to get a resource of a particular type given an id and be able to call Clear on all 25 caches. Something like class Manager { public: /// Returns Cache<Resource>::Retrieve( id ) template< typename Resource > const Resource& Get( ResourceId id ); /// Calls Cache::Clear for all resource types void Clear(); }; It would be pretty easy to just copy and paste it out 25 times but I would like to reduce code duplication and simplify maintenance through metaprogramming. I have a private boost::mpl::list25 named resource_list containing all the resource types. I think I need to transform that in to a boost::fusion::map of 25 Resource to Cache<Resource> pairs but I'm not sure that is what I really need to do or how to go about doing that. Thanks, Michael Marcin

2 6

Header error in boost/python/object/make_holder?
by Michel Valstar 15 Oct '07

15 Oct '07

Hello, I am trying to build code of a recently graduated student, who is now unavailable to us (read: ignores us). When running scons in the appropriate directory, a lot gets build, until I get the following error: /usr/include/boost/python/object/make_holder.hpp:81: error: 'allocate' is not a member of 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >' /usr/include/boost/python/object/make_holder.hpp:83: error: no matching function for call to 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder(int*&)' /usr/include/boost/python/object/value_holder.hpp:44: note: candidates are: boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder() /usr/include/boost/python/object/value_holder.hpp:44: note: boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder(const boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >&) scons: *** [trackerbase/trackerbasewrapper.os] Error 1 scons: building terminated because of errors. This does not seem to be an error in his own code, rather an error in the boost.python code? This is the first time I am using boost, and, as usual, I need to get this program working yesterday. My machine is a recently installed Ubuntu Feisty (hence the need for re-compilation). I am using the latest version of Boost (boost_1_34_1) and python 2.5.1 Any help would be appreciated. Thanks, MIchel -- Michel Valstar, PhD candidate http://www.doc.ic.ac.uk/~mvalstar Department of Computing Imperial College London 180 Queens' Gate London SW7 2AZ, U.K. tel.: +44 20 7594 8225 fax: +44 20 7581 8024

2 1