November 2006 - Boost-users - lists.preview.boost.org

Iterater for subset extraction?
by Thom DeCarlo 12 Nov '06

12 Nov '06

I have a couple of n00b questions. I have constructed a BGL graph that uses the edge_name_t property to road names. I want to change the weights of some of the roads based on input from the user. Is there a way to set up an iterator to step through edges that have names which match elements of a set? (e.g., "A,B,B1,L,M") In a related question, I need to extract a vertex whose vertex_index_t value matches a specific value. The vertices were not entered in any specific order, so the "vertex(1, g)" function returns the first vertex to have been entered into the graph, but not necessarily the one whose index value is "1". Thanks, Thom -- this sig intentionally left blank

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format un-debuggability
by Drumheller, Michael 12 Nov '06

12 Nov '06

If you don't pass enough arguments to a boost::format you get this: "boost::too_few_args: format-string refered to more arguments than were passed" Unfortunately there is, as far as I can tell, no way to figure out where the error happened, other than building a debug version of your app and breaking into the debugger on that error. Needless to say that can be very inconvenient. Would it be possible to fix boost::format (which, by the way, is IMHO one of the most wonderful of all the Boost libraries!!) so that its exceptions carry a little more information about their origins (e.g., embedding the format-string itself in the message)? Thank you. Michael Drumheller Boeing Phantom Works Mathematics and Engineering Analysis 425.373.2703 michael.drumheller(a)boeing.com This email may contain proprietary information. If you are not the intended recipient please delete it and notify the sender that you received it in error.

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Boost crosscompilation
by Vinh 12 Nov '06

12 Nov '06

Hi everyone, I'm new to boost and have successfully installed it on my debian sarge system. For a particle Filter using the Bayes++ Library, I would need to crosscompile the boost library for an ARM processor. Does anyone know whether that is possible? (I already have a crosscompiler installed, but don't know whether boost supports crosscompilation?) Vinh

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iterating over arbitrary python object in c++
by Augusto Callejas 12 Nov '06

12 Nov '06

hi- i'm writing a C++ class that i want to expose as a python class. one method in my class has an argument that takes in a python object that "implements" the iterator interface (that is the python object has defined "__iter__" and "__next__" and can be used in a "for x in y" loop). how do i go about iterating over that python object in my C++ code? for example: void my_class::method(object my_iterable_obj) { // iterate over "my_iterable_obj" } one method i tried was calling the "__next__" method explicity: my_iterable_obj.attr("__next__")() however, "__next__" raises a StopIteration exception when there are no more objects in the iterator. i could not find any examples in the boost python tutorials for handling python exceptions from c++. is there another way i can go about this? thanks, augusto.

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[Boost.Signals] in Multithreaded Environment
by Terry G 11 Nov '06

11 Nov '06

Hello again everyone! Boo ST == (Scarey signals & threads) Signals/slots are just too good not to use in a multi-threaded environment. Someday, this will be fixed, I know. But for now... I'm trying to serialize access to boost.signals using Bjarne Stroustrups "wrapper" concept. Here's what I'm doing. Is this likely to cause problems? Sorry about the length. If this is too dangerous, what's a better alternative? I typed this from memory and didn't try to compile. Please disregard any typos or syntactic blunders. // Implements Bjarne Stroustrup's "wrapper" concept using boost::shared_ptr. template <typename T> class Wrapper { T* p; public: explicit Wrapper(T& obj) : p(&obj) { } boost::shared_ptr<T> get() const { p->prefix(); return boost::shared_ptr<T>(p, boost::mem_fn(&T::suffix)); } // get boost::shared_ptr<T> operator->() const { return get(); } }; //Wrapper // Provides signals through "safe" wrapper. (?) class TiePoint { public: class Events { Mutex lock; // Provided elsewhere. void prefix() { lock.acquire(); } void suffix() { lock.release(); } friend class Wrapper<Events>; public: boost::signal<void (Signal1Args)> signal1; boost::signal<void (Signal2Args)> signal2; // etc... template <class Iter> void disconnect(Iter begin_, Iter end_) { std::for_each(begin_, end_, boost::mem_fn(&boost::signals::connection::disconnect); } // disconnect }; // Events private: Events _events; public: Wrapper<Events> events; TiePoint() : _events(), event(_events) { } }; // TiePoint // Demonstrates use of TiePoint class. class UsesSignals { private: void handle1(Signal1Args) { ... } void handle2(Signal2Args) { ... } std::vector<boost::signals::connection> conns; // Be very careful with these. public: void connect(TiePoint& tiePt) { boost::shared_ptr<TiePoint::Events> events = tiePt.events.get(); conns.push_back(events->signal1.connect(Handle1)); conns.push_back(events->signal2.connect(Handle2)); } // connect void disconnect(TiePoint& tiePt) { tiePt.events->disconnect(conns.begin(), conns.end()); conns.clear(); } // disconnect void signalJustOne(TiePoint& tiePt) { tiePt.events->signal1(signal1args); } // signalJustOne void signalMany(TiePt& tiePt) { boost::shared_ptr<MyClass::Events> events = tiePt.events.get(); events->signal1(signal1args); events->signal2(signal2args); ... } // signalMany }; // UsesSignals

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Serialization of an std::list into XML without a NVP
by Devin Fallak 10 Nov '06

10 Nov '06

Hi all, I'm working with the Serialization library and trying to output a list of objects into an XML file. The problem I'm having is that in serializing a std::list, the Serialization library requires that the list itself is given a NVP. The specification I'm working with requires a list of undefined length WITHOUT its own NVP. Is there any way to serialize a std::list into/out of an xml_oarchive/xml_iarchive? Any help would be much appreciated. Thanks, Devin Fallak

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Problem with counting iterator and bind
by Maitre Bart 10 Nov '06

10 Nov '06

I have this: typedef LegacySequentialContainer<string> LegacyStringVector; LegacyStringVector lsv; // ... filling lsv with strings ... I realized this: boost::counting_iterator<int> it(0); boost::counting_iterator<int> end(lsv.length()); while (it < end) cout << boost::bind(&LegacyStringVector::operator[], v3, _1)(*it++) << " "; cout << "\n"; and it works. However, I wish to do the same but using std::copy or std::for_each instead. I tried the following but none is able to compile: copy(boost::counting_iterator<int>(0), boost::counting_iterator<int>(v3.size()), boost::bind(ostream_iterator<string>(cout, " "), &vector<string>::operator[], v3, _1)); copy(boost::counting_iterator<int>(0), boost::counting_iterator<int>(v3.size()), boost::bind(ostream_iterator<string>(cout, " "), boost::bind<string,int>(&vector<string>::operator[], v3, _1))); copy(boost::counting_iterator<int>(0), boost::counting_iterator<int>(v3.size()), boost::bind(ostream_iterator<string>(cout, " "), boost::bind<string,int>(&vector<string>::operator[], v3), _1)); I must be close to the solution but error messages do not help guiding me in the right direction. Anyone has any suggestion?

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reference to void in shared_ptr_nmt
by Oliver Kania 10 Nov '06

10 Nov '06

Hello, I am encountering the following problem when using boost with shared pointers (Ubuntu Edgy, G++4.1/4.0/3.4): ======================= /usr/include/boost/detail/shared_ptr_nmt.hpp:115: error: forming reference to void shared_ptr_nmt.hpp:114: error: forming reference to void ========================== the source code reads : ========================= T & operator*() const // never throws { BOOST_ASSERT(px != 0); return *px; } ========================= To me, this seems like a g++ (GNU GCC) problem, (It seems that G++ checks if void would be a viable substitutiion for T) however, I have tried three different versions of g++ and get the same result every time. There once was such a bug in GCC but it has been resolved ages ago. Regards, Oliver Kania

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Building Boost on Solaris 10/Sparc: No release version of libraries?
by Boris 10 Nov '06

10 Nov '06

I built Boost 1.33.1 on a Solaris 10/Sparc machine. Problem is that no release version of the various libraries are built. There is for example libboost_date_time-gcc-d-1_33_1.so but no libboost_date_time-gcc-mt-s-1_33_1.so. Is this a known problem on Solaris? The Solaris machine has GCC 3.4.6 installed. I built bjam myself (with tools/build/jam_src/buid.sh) and then entered: ./bjam "-sTOOLS=gcc" "-sBUILD=<define>NO_BZIP2" --without-python stage When I look then into stage/lib there are only debug versions of the libraries? Boris

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[WAVE] position of tokens
by Andreas Sæbjørnsen 10 Nov '06

10 Nov '06

Hi, I need some advice regarding Wave. What I want to do is to operate with Wave on a token stream and extract the token stream representing macro calls after expansion. The twist is that I want the token stream after expansion to have the positions that another preprocessor would see on the already expanded output from Wave. E.g: #define MACRO_CALL int x; int main(){ MACRO }; Exands into #line 2 int main(){ int x; }; Where 'int x' should have a position of line 3 instead of line 1 after expansion. I also want the column number to represent what we see on line 3 instead of what we see on line 1. Is this possible ? Thanks Andreas

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