June 2007 - Boost-users - lists.preview.boost.org

Performing static_cast<shared_ptr<base>*> on a shared_ptr<derived>*. Any guarantees?
by Pete Bartlett 11 Jun '07

11 Jun '07

I have taken over some code that boils down to ///begin code #include <iostream> #include <boost/shared_ptr.hpp> struct base { int i; base(int i_):i(i_) {} }; struct derived : base { derived(int i): base(i) {} }; int main() { boost::shared_ptr<derived> pd(new derived(5)); void* ptr_to_pd = &pd; boost::shared_ptr<base>* ptr_to_pb = static_cast< boost::shared_ptr<base>* >(ptr_to_pd); std::cout << "\n" << (**ptr_to_pb).i ; //Prints 5 } ///End code Now shared_ptr<B> and shared_ptr<A> are unrelated types, so IIUC there is no guarantee that this will work. Is that right? I know from the shared_ptr documentation that I should refactor in the direction of dynamic_ptr_cast (though complications not shown in the code above make that harder that). However for the time being this code appears to be working. Is that just a fluke? I.e. I am relying on the author of boost::shared_ptr and/or my compiler creators not to do something such that it doesn't work. Is there the possibility that any memory could be deleted twice? Or I am worrying over nothing and in fact there is a reason why the above is safe? Many thanks for any advice you can provide, Peter Bartlett

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[bind] Help with functional composition of shared_ptr::use_count in std::map
by Hughes, James 11 Jun '07

11 Jun '07

Hello all, I'm trying to use bind to help with removeif in a std::map<string, shared_ptr<something> >. I want to remove items where the shared_ptr use_count is 1. map<string, shared_ptr<data> > Fred; RemoveIf(Fred.begin(), Fred.end(), boost::bind(std::equal_to<long>(), 1, boost::bind(&map<string, shared_ptr<data> >::value_type::second::use_count, _1) ) However, I get a compile error on ::second not being a class or namespace. Anyone know how I should do this? I'm a beginner at boost::bind, so be gentle.... James This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. Any unauthorized disclosure, copying, distribution or reliance on the contents of this information is strictly prohibited and may constitute a violation of law. If you are not the intended recipient, please notify the sender immediately by responding to this e-mail, and delete the message from your system. If you have any questions about this e-mail please notify the sender immediately.

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Re: [Boost-users] [bind] Help with functional compositionofshared_ptr::use_count in std::map
by Küppers, Ben 11 Jun '07

11 Jun '07

> map<string, shared_ptr<data> > Fred; > > RemoveIf(Fred.begin(), > Fred.end(), > boost::bind(&map<string, shared_ptr<data> > >::value_type::second::unique, _1) > ) James, remove_if requires an assignment operator on the operated type but the value_type of a map is defined as std::pair< const T1, T2 >. The const on the first type will cause any assignment to fail. In other words, you can't use remove_if on a map. That said, in order to fix your bind you would need two functors. The type passed to the bind is the value_type of the map which is by definition a pair. You need to first invoke a functor on the pair to extract the second member and then call the member unique on the resulting smart pointer. In order to do so you'll need to write your own extractor, because the STL does not provide a functor to obtain the "second" field from a pair (I haven't found one in boost either). template< class Pair > struct second_of : std::unary_function< Pair, typename Pair:second_type > { typename Pair::second_type opertator()( const Pair& the_pair ) const { return the_pair.second; } }; std::for_each( Fred.begin(), Fred.end(), boost::bind( boost::shared_ptr< data >::unique, boost::bind( second_of< std::map< std::string, boost::shared_ptr< data > >::value_type >(), _1 ) ) ); Note that you can call for_each as it does not require the assignment operator. Hope this helps, Ben This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.

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Problems with boost.thread
by luca regini 11 Jun '07

11 Jun '07

I have some problems with boost.thread (version 1_34) under gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-52). The library ( all the boost distribution) compiles fine and a bjam on the ./libs/thread/test directory also report a successful test execution. However when i try to explicitly link one of the example (tread_group with the boost tread library using the following command line: g++ -I/opt/six/boost_1_33_1 -I/opt/six/boost_1_34/include/boost-1_34 -pthread -o mytest thread_group.cpp libboost_thread-gcc32-mt-d-1_34.so.1.34.0 i get a segmentation fault. >From a core dump i can see the following stacktrace: 0 0x008e78fb in boost::function0<void, std::allocator<boost::function_base> >::assign_to_own (this=0xb75e5420, f=@0xbfffacb0) at ../../../boost/function/function_template.hpp:647 647 f.vtable->manager(f.functor, this->functor, (gdb) backtrace #0 0x008e78fb in boost::function0<void, std::allocator<boost::function_base> >::assign_to_own (this=0xb75e5420, f=@0xbfffacb0) at ../../../boost/function/function_template.hpp:647 #1 0x008e748f in function0 (this=0xb75e5420, f=@0xbfffacb0) at ../../../boost/function/function_template.hpp:527 #2 0x008e6748 in thread_proxy (param=0xbfffac20) at ../../../libs/thread/src/thread.cpp:106 #3 0x0040f371 in start_thread () from /lib/tls/libpthread.so.0 #4 0x001d8ffe in clone () from /lib/tls/libc.so.6 Where is the problem?? Thanks in advance, Luca Regini

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Question about boost mutex
by Meryl Silverburgh 11 Jun '07

11 Jun '07

Hi, I have a application which uses p_thread for creating threads, can i use the boost mutex classes for thread synchronization? Or the boost mutex class only works with boost thread class? Thank you.

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[program options] & also an apology to the list...
by jono 10 Jun '07

10 Jun '07

...for my earlier grumpy email about program_options. i'm was wanting to pass some sequences to some options using boost::program_options. something like: [me@here ~]$program --opt1 1 2 3 4 --opt2 5 6 7 8 --opt3 xxx yyy zzz if i use desc.add_options("opt1", value< vector<string> >()->multitoken(), "...") i get all the tokens to the end of the line. can i make multitoken() stop eating tokens by recognizing a syntactic element; either an option specifier or a token it can't interpret as a required type? can i inherit from the value_semantic class to read multiple tokens maybe? this whole library is very interesting but subtle. i do better when i can read examples of working code. does anyone know a more extensive discussion of it besides the distibution docs? ...which are great by the way! cheers jono

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Problem with boost::program_options
by Jonas Bösch 10 Jun '07

10 Jun '07

Hi, I'm having a problem with boost::program_options. I attached a stripped-down version of the code that demonstrates the problem. I have a number of positional arguments ( "ops" ), and one normal argument ( "input-file,i" ). Now, if i run the program ./op_test pos0 pos1 pos2 -i non_positional it interpretes the "non_positional" as further positional arg, and not as parameter belonging to -i. Any hints on how to solve this are greatly appreciated. I ran it on: Mac OS X 10.4 on a G5, with the latest XCode ( gcc 4.0.1 ) boost 1.34 Jonas

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BGL: INTERNAL COMPILER ERROR in VC7.1
by Yariv Tal 10 Jun '07

10 Jun '07

This one was already posted by Nicholas Burlett awhile back (see http://lists.boost.org/MailArchives/boost-users/msg06534.php) but I have some new info that may help. The problem: ========= When compiling code that uses the boost.graph library the VC7.1 compiler shouts: c:\boost_1_32_0\boost\mpl\aux_\preprocessed\plain\apply_wrap.hpp(48) : fatal error C1001: INTERNAL COMPILER ERROR As Nicholas already noted, this seems to be due to some compiler problem with the boost.graph out_edge_iterators since it is caused by the following lines in my code: (FilteredGraphGenerator::FilteredGraph is a typedef of a boost::filtered_graph) typedef boost::graph_traits<FilteredGraphGenerator::FilteredGraph> ::out_edge_iterator oedge_iterator; oedge_iterator edgesItr, edgesEnd; boost::tie(edgesItr, edgesEnd) = boost::out_edges(itr->first, m_g.m_filteredGraph); while (edgesItr != edgesEnd) { // do anything! } In fact, it seems to be related to the operator!= between iterators (if the while loop is commented out it compiles). How ever, the error persists even after changing the operator!= to operator== : while (edgesItr == edgesEnd) { // do anything! } ========================================================================== Some findings: =========== * We used to use boost_1_30_0 and the code used to compile PERFECTLY. The problem only appeared after migrating to boost_1_32_0. * Calling directly to the "equal" function in iterator_core_access instead of the operator== works. typedef boost::graph_traits<FilteredGraphGenerator::FilteredGraph> ::out_edge_iterator oedge_iterator; oedge_iterator edgesItr, edgesEnd; boost::tie(edgesItr, edgesEnd) = boost::out_edges(itr->first,m_g.m_filteredGraph); while (boost::iterator_core_access::equal(edgesItr, edgesEnd, boost::mpl::true_())) { // do somthing } * The error message location is at the mpl::apply_wrap2 function. Any relation to the mpl::apply2 function used for declaring the operator== in the BOOST_ITERATOR_FACADE_INTEROP_HEAD macro? Have these functions changed since v1.30.0?

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Problem with ProgramOptions
by Jonas Boesch 10 Jun '07

10 Jun '07

Hi, I'm having a problem with boost::program_options. I attached a stripped-down version of the code that demonstrates the problem. I have a number of positional arguments ( "ops" ), and one normal argument ( "input-file,i" ). Now, if i run the program ./op_test pos0 pos1 pos2 -i non_positional it interpretes the "non_positional" as further positional arg, and not as parameter belonging to -i. Any hints on how to solve this are greatly appreciated. My machine: Mac OS X 10.4 ppc ( G5 ) XCode 2.4.1 ( gcc 4.0.1 ) boost 1.34 Greetings, Jonas The code: // ------------------------ options.h ------------------- #ifndef __VMML__OPTIONS__H__ #define __VMML__OPTIONS__H__ #include <boost/program_options.hpp> #include<map> namespace vmml { namespace boost_po = ::boost::program_options; typedef ::boost::program_options::variables_map var_map; class options { public: options(); void setup( int argc, char* argv[] ); void get_operator_chain( std::vector< std::string >& op_chain ); protected: // generic options boost_po::options_description _generic_options; // op chain boost_po::options_description _all_options; std::map< std::string, boost_po::options_description* > _op_descs; // positional options boost_po::positional_options_description _positional_desc; boost_po::variables_map _options_map; std::vector< std::vector< std::string > > _op_cfgs_from_file; };//class options };//namespace vmml #endif // --------- options.cpp -------------------------------- #include "options.h" #include <iostream> #include <vector> #include <string> namespace vmml { options::options() : _generic_options( "Generic options" ) { _generic_options.add_options() ("input-file,i", "specify input file") ("ops,O", boost_po::value< std::vector< std::string > >()- >composing(), "specify operators " ) ; _positional_desc.add( "ops", -1 ); } void options::setup( int argc, char* argv[] ) { _all_options.add( _generic_options ); boost_po::store( boost_po::command_line_parser( argc, argv ) .options( _all_options ) .positional( _positional_desc ) //.allow_unregistered() .run(), _options_map ); boost_po::notify( _options_map ); } void options::get_operator_chain( std::vector< std::string >& op_chain ) { if ( _options_map.count("ops") ) { const std::vector< std::string >& ops = _options_map["ops"].as< std::vector< std::string > >(); op_chain = ops; } } }//namespace vmml int main( int argc, char** argv ) { vmml::options opt; opt.setup( argc, argv ); std::vector< std::string > ops; opt.get_operator_chain( ops ); std::vector< std::string >::iterator it = ops.begin(); std::vector< std::string >::iterator itend = ops.end(); for( ; it != itend; ++it ) { std::cout << *it << std::endl; } }

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[boost.python] is it possible to make python::dict wrap an existing python dictionary object instead of making a copy?
by Marcin Kalicinski 10 Jun '07

10 Jun '07

python::dict m_mainNamespace = python::dict(m_mainModule.attr("__dict__")); The above code makes a copy of mainModule dictionary. Is it possible to make m_mainNamespace not a copy but a reference to mainModule dictionary? Marcin

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