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Field of record as boost::any
by Mateusz Łoskot 09 Jan '06

09 Jan '06

Hi, Is boost::any suitable to use it as a type of field of record? Record is a set of fields. Every field may store value of different type: int, double, char*. Usually, in this case I'd use union of int,double and char*. But I'd like to solve it a better way, more C++ than C. So, would you recommend boost::any as a type of field value? Cheers -- Mateusz Łoskot http://mateusz.loskot.net

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Is boost::filesystem::path unable to deal with hidden unix dircetories?
by Hendrik Belitz 09 Jan '06

09 Jan '06

Dear boost users and developers, I just encountered a minor problem in boost::filesystem::path which seems to be unable to deal with hidden unix directories ( == names preceeded by an dot '.' character ). Is there any way to generate a valid path object for paths like "/foo/.bar"? Trying to create such an object from a C++ string results in an exception getting thrown. ------------------------------------------------------------------------------------- Dipl.-Inform. Hendrik Belitz Central Institute of Electronics / Zentralinstitut für Elektronik Multimodal image processing workgroup / AG Multimodale Bildverarbeitung Research Center Juelich / Forschungszentrum Jülich GmbH D-52428 Jülich, Germany Tel.: (++49)2461 61 8701 Fax: (++49)2461 61 3990 email: h.belitz(a)fz-juelich.de ggp-key available via http://pgpkeys.pca.dfn.de

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[MSVC7.0] functions missing when BOOST_NO_MEMBER_TEMPLATES is defined
by Allen Zhao 09 Jan '06

09 Jan '06

Hi, All, As I am working to get libtorrent working on Win32 with MSVC 7.0, I notice that BOOST_NO_MEMBER_TEMPLATES is defined by default. As a consquence, some of the functions in multi_index_container.cpp is not defined. For example, #if !defined(BOOST_NO_MEMBER_TEMPLATES) template<int N> struct nth_index { BOOST_STATIC_ASSERT(N>=0&&N<mpl::size<index_type_list>::type::value); typedef typename mpl::at_c<index_type_list,N>::type type; }; template<int N> typename nth_index<N>::type& get(BOOST_EXPLICIT_TEMPLATE_NON_TYPE(int,N)) { BOOST_STATIC_ASSERT(N>=0&&N<mpl::size<index_type_list>::type::value); return *this; } template<int N> const typename nth_index<N>::type& get( BOOST_EXPLICIT_TEMPLATE_NON_TYPE(int,N))const { BOOST_STATIC_ASSERT(N>=0&&N<mpl::size<index_type_list>::type::value); return *this; } #endif Is there anything to enable these functions when BOOST_NO_MEMBER_TEMPLATES is undef? Any suggestions? Best regards, Allen Zhao

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Misuse of shared_ptr?
by Pooyan McSporran 09 Jan '06

09 Jan '06

Hi, (Using gcc 4.0.2, boost 1.33.1, linux) I've got a program which causes segfaults using shared_ptr. I've reduced the program as far as I can to show the fault without any extra fluff. It looks as if an object pointed to by a shared_ptr is being deleted more than once. What I'm trying to do is to have an instance of Memory 'know' about an instance of Foo. This is currently being done with a shared_ptr. It appears that I'm misusing shared_ptr in the assignment, but I'm unsure as to what the right way is. Alternatively, I probably could use a reference instead of a shared_ptr, but I'm not sure if the Foo instance will always exist. Thanks in anticipation. #include <cstdlib> #include <iostream> #include <string> #include <boost/shared_ptr.hpp> class Memory; typedef boost::shared_ptr<Memory> MemoryPtr; class Foo; typedef boost::shared_ptr<Foo> FooPtr; class Memory { public: Memory () : fp () { std::cout << "Constructed Memory" << std::endl; }; virtual ~Memory () { std::cout << "Destructing Memory" << std::endl; std::cout << "fp.use_count=" << fp.use_count () << std::endl; }; void remember1 (FooPtr f) { std::cout << "Remembering" << std::endl; fp = f; }; private: FooPtr fp; }; class Foo { public: Foo (const std::string& name_) : name (name_) { std::cout << "Constructed Foo '" << name << "'" << std::endl; }; virtual ~Foo () { std::cout << "Destructing Foo '" << name << "'" << std::endl; }; void test (MemoryPtr m) { m -> remember1 (FooPtr (this)); } private: const std::string name; }; int main () { { FooPtr f1 (new Foo ("first")); MemoryPtr m1 (new Memory ()); f1 -> test (m1); } return EXIT_SUCCESS; }

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[program_options] How to use unknown program options?
by Vsevolod Vlaskin 09 Jan '06

09 Jan '06

Hi, I am trying to allow unknown options in the command line of my application (as described in "Allowing Unknown Options" section of program_options docs). Here is the code snippet: //----------------------------------------------------- boost::program_options::options_description my_options("Options"); my_options.add_options() /* adding some allowed options */ ; boost::program_options::variables_map vm; boost::program_options::store( boost::program_options::command_line_parser( ac, av ).options( my_options ).allow_unregistered().run(), vm ); boost::program_options::notify( vm ); //----------------------------------------------------- If an option is not specified in my_options, the call boost::program_options::store() above throws exception "unknown option". (I checked that it is store() that throws.) Does anyone have any suggestions how I could store and access the option values in this case? Of course, I can use basic_parsed_options returned by run(), but it seems to defeat the convenience of the library. Is there any way to use store() and variables_map in this case? Thank you for help. Best regards, Vsevolod Vlaskine __________________________________________ Yahoo! DSL Something to write home about. Just $16.99/mo. or less. dsl.yahoo.com

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Mutually exclusive options in boost::program_options?
by Marshall Clow 09 Jan '06

09 Jan '06

I'm trying to use boost::program_options for the first time, and there's a couple things that I am tripping over. The first is the idea of mutually exclusive options. I can't find any support for them in the library, and that surprises me - to the point of asking for help. I have two options, only one of which can be specified; say -frtti and -fno_rtti (say). The other one is that program_options, by default, wants to use double hyphens to define options: "foo --option1 --option2" I'm a lot more comfortable with single hyphens: "foo -option1 -option2" Am I missing something basic here? -- -- Marshall Marshall Clow Idio Software <mailto:marshall@idio.com> It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shaking, the shaking becomes a warning. It is by caffeine alone I set my mind in motion.

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Error when including date_time files
by Rob Marsden 09 Jan '06

09 Jan '06

I am having trouble with some date_time files. The following code (from the boost documentation): #include "boost/date_time/posix_time/posix_time.hpp" #include "boost/date_time/local_time_adjustor.hpp" #include "boost/date_time/c_local_time_adjustor.hpp" #include <iostream> int main() { return(0); } gives me errors C:\LOCAL\INCLUDE/boost/date_time/posix_time/time_formatters_limited.hpp(77): error: more than one operator "<<" matches these operands: function "std::basic_ostream<_E, _Tr>::operator<<(std::_Bool={bool={bool}}) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(short) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(unsigned short) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(int) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(unsigned int) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(long) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(unsigned long) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(float) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(double) [with _E=char, _Tr=std::char_traits<char>]" function "std::basic_ostream<_E, _Tr>::operator<<(long double) [with _E=char, _Tr=std::char_traits<char>]" operand types are: std::basic_ostream<char, std::char_traits<char>> << boost::posix_time::time_duration::fractional_seconds_type << frac_sec; ^ C:\LOCAL\INCLUDE/boost/date_time/posix_time/time_formatters_limited.hpp(140): error: more than one operator "<<" matches these operands: ...similar ^ C:\LOCAL\INCLUDE/boost/lexical_cast.hpp(156): error: no operator ">>" matches these operands operand types are: std::basic_stringstream<char, std::char_traits<char>, std::allocator<char>> >> boost::int64_t stream >> output && ^ detected during: instantiation of "bool={bool} boost::detail::lexical_stream<Target, Source>::operator>>(InputStreamable &) [with Target=boost::int64_t={__int64}, Source=boost::detail::array_to_pointer_decay<std::basic_string<char, std::char_traits<char> , std::allocator<char>>>::type, InputStreamable=boost::int64_t={__int64}]" at line 221 instantiation of "Target boost::lexical_cast<Target,Source>(const Source &) [with Target=boost::int64_t={__int64}, Source=std::basic_string<char, std::char_traits<char>, std::allocator<char>>::_Myt]" at line 94 of "C:\LOCAL\INCLUDE/boost /date_time/time_parsing.hpp" instantiation of "time_duration boost::date_time::parse_delimited_time_duration<time_duration>(const std::string &) [with time_duration=boost::posix_time::time_duration]" compilation aborted for C:\Research\DogWood\TextAnalysis\Parser\BoostTest\BoostTest.cpp (code 2) Error executing xicl6.exe. The environment is compiler Intel v9.0 in the VC6 IDE under Win2k Can anyone suggest a solution? -- Rob Marsden Gistix (Northern) Limited

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[MPL] sorting sequence according to inheritance hierarchy
by Slawomir Lisznianski 09 Jan '06

09 Jan '06

Hello, I'm trying to find a solution to the following problem. Given types A, B and C such that C is derived from B and B is derived from A, and a sequence S1 which stores A, B and C (in arbitrary order): 1) transform S1 so resulting sequence S2 would have elements sorted according to their relative position within their inheritance hierarchy (say, most derived first). 2) when one introduces another type, D, which doesn't inherit from any of A, B or C, after sorting S1, it would end up at the end of S2. 3) the solution needs to be unintrusive for the "input" types, that is, it ought to work for existing types. Example ------- Input: S1 = { A, C, D, B }; Expected result, after sorting: S2 = { C, B, A, D }; Purpose ------- By finding a way to sort S1 according to predicates listed above, I hope to come up with a generic exception-handling mechanism (used in RPC-like library), example: typedef vector<E0, E1, .. ,En> sorted_exception_decl; try { func(); } catch(at<sorted_exception_decl, int_<0> >::value const & E0) { .. } catch(at<sorted_exception_decl, int_<1> >::value const & E1) { .. } catch(at<sorted_exception_decl, int_<n> >::value const & En) { .. } Your thoughts on how sane this idea is are greatly appreciated. -- Slawomir Lisznianski Paramay Group, LLC "Programs for Research Machinery"

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date_time: convert to and from a timeval
by Thomas Lemaire 09 Jan '06

09 Jan '06

Dear list, I would like to convert ptime and time_duration to and from the standard timeval type. So that I can use all the operators available for ptime and time_duration I found that this topic has already been discussed here: http://lists.boost.org/Archives/boost/2003/06/49197.php The conclusion was: "" Ok will do. I'll add some protections or rounding for when durations support higher than microsecond resolution. I'll let you know when this gets added. Thx, Jeff "" This message was sent on 2003-06-23. I cannot find any thing related to timeval in the doc of boost 1.33. Did I miss something ? Also doc about xtime in boost.threads does not help that much... http://www.boost.org/doc/html/xtime.html cheers, -- thomas

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iterators
by jens-theisen＠gmx.de 09 Jan '06

09 Jan '06

Hello, Say a library programmer wants to make a virtual interface to his class with a function that returns a collection of things. Usually one end up writing something silly like class interface { ... virtual std::vector< ... > give_stuff() const; }; which has some disadvantages, the most important being: - The implementing function must calculate the whole result, even if some of it might not be needed. Especially infinite collections of things are not possible in this way. - The vector is a container and that's a poorly defined concept. As a consequence, we can't do very much with it. For instance, you can't write give_stuff() + give_more_stuff() to concatenate. Though it's easy to implement that, we really don't want to do this on the basis of containers in general and we also don't want to do it again and again in every single project for std::vector in particular. - As the library gets used, it's poor interface is carved in stone, and so are the other two problems for it. The first problem can be addressed by using an iterator to some container. We obviouly can't use an iterator to a vector since that wouldn't solve any problems. It has to be a custom iterator class lib_iterator_impl : ... { ... virtual ... dereference() const; virtual ... advance() const; }; class lib_iterator { ... lib_iterator(lib_iterator_impl const* impl); }; class interface { ... virtual lib_iterator give_stuff() const; }; where lib_iterator_impl than has to be extended by the client of the library. Actually, there is no real need for lib_iterator to be a proper iterator in the standard sense. Especially, such iterators could be aware of there ends (or even their beginnings) to make it unnecessary to have always two of them. Both the virtualisation and halving the number of those iterators would also reduce the complexity of error messages. On such a framework, many small building blocks could be build, like concatenation, filtering, mapping, cartesian products, etc. In my opinion, at least the very low-level parts of such a framework are so important that they belong in boost. My question at this point is in what regard people share this opinion and to what extend we already have these things. I have heard of any_iterator in the past, but I can't find anything about it in the boost malings list archives or google, which would be related to this. Other than this, I'm not aware of anything in this regard. Cheers, Jens

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