Dynamic casts returns null when library with C++ python extensions is used as a plugin on RHEL5 -

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i have library c++ python extensions (c++ calls python in turn calls c++) using boost::python , python libraries (this messy, lot of legacy) when tested standalone works correctly. in particular, dynamic_cast works correctly.

but when library packaged use plugin on rhel5 using gcc 4.1.2 external application, dynamic_cast returns null resulting in application not working expected. on windows (tested vista 64 bit using visual studio 2005 , 2008) works fine. when debugged using ddd instance, able see pointer before casting has right type_name (slightly mangled compiler usual, suppose?). specific debugging tips here of help.

a reinterpret_cast solved problem. while baulked at, @ loss how proceed, esp. since due issues external app. convoluted mess , seems futile, if can here sample code. following c++ snippet creates "smart_handle" queue python commands stored in string "input". string import imports locations , definitions of functions called boost::python::exec(..) in function call py_api::execute_py_command:

boost::shared_ptr<my_base_class>           processor(new my_derived_class()); std::map<std::string, smart_handle> context; context.insert(std::make_pair<std::string, smart_handle>("default_queue",                 make_smart_handle(processor))); const std::string py_command =        import +         "namesp.dialects.cpython.set_command_queue('default', default_queue)\n" +         input; if( !py_api::execute_py_command(py_command, context) ) {   return false;  }

the make_smart_handle defined as:

template <typename type_t>  const smart_handle make_smart_handle(const boost::shared_ptr<type_t>& ptr) {    if( !ptr ) {       return smart_handle();    }    return smart_handle(new detail::smart_handle_weak_impl<type_t>(ptr)); }

the function set_command_queue defined in python __init__.py as:

import func1  import func2 import func3 import func4  command_queue_map = {} def set_command_queue(queue_name, object): command_queue_map[queue_name] = object def get_command_queue(queue_name = 'default'): return command_queue_map[queue_name]

now actual python functions func1, func2, etc. defined in separate python files calls c++ functions defined under namespace "namesp". first line of these c++ functions recover "smart_handle" "queue" by:

boost::shared_ptr<my_base_class> queue = smart_handle_cast<my_base_class>(handle).lock();

it in above function smart_handle_cast dynamic_cast used returns null, when library used plugin in external app. using reinterpret_cast allows work correctly. smart_handle_cast returns const boost::weak_ptr. interested, here defintion of smart_handle_cast<..>() function:

template <typename type_t>  const boost::weak_ptr<type_t> smart_handle_cast(const smart_handle& handle, bool        throw_if_failure) {    if( !handle.is_valid() ) {        if( throw_if_failure ) {           throw smart_handle::bad_handle("bad handle, attempting access invalid                                            handle");        }        //-no throw version returns non-initialized weak pointer        return boost::weak_ptr<type_t>();    }    //-this line fails @ run time , returns null.    const detail::smart_handle_weak_impl<type_t>* casted = dynamic_cast<const                     detail::smart_handle_weak_impl<type_t>* >(handle.impl());    if( !casted ) {        if( throw_if_failure ) {            throw smart_handle::bad_handle_cast("bad handle cast, attempting \               convert incorrect pointee type");        }        //-no throw version returns non-initialized weak pointer        return boost::weak_ptr<type_t>();    }    return casted->pointee; }

take @ similar question , gcc faq

if use dlopen explicitly load code shared library, must several things. first, export global symbols executable linking "-e" flag (you have specify "-wl,-e" if invoking linker in usual manner compiler driver, g++). must make external symbols in loaded library available subsequent libraries providing rtld_global flag dlopen. symbol resolution can immediate or lazy.


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