August 2008 - Boost-users - lists.boost.org

EqualityComparable of unordered containers
by Daniel Krügler 22 Aug '08

22 Aug '08

Hello, I would like express my respect and congratulations for the provision of boost 1.36 (which had an impressive short release cycle)! One of the very promising new contributions is Boost.Unordered and I I would like to make a comment on the provision of operator==/operator!= as explained in http://www.boost.org/doc/libs/1_36_0/doc/html/unordered/rationale.html#unor… I totally agree that there exist valid and reasonable use-cases for EqualityComparable for unordered containers. In fact many unordered containers (usually named hash containers) exists in one or the other language or user-defined library which provide some form of "unordered" equality comparison, which reflects the unordered nature of the container itself and thus matches a typical user expectation. Nevertheless there exists an unfortunate side-effect of the current implementation of operator== and operator!=, which should be mentioned in the documentation IMO. To keep a long story short: Under some given conditions, EqualityComparable of Boost.Unordered containers will violate the very basic "symmetry" property of EqualityComparable. This can happen, if the equality predicate key_eq() is a runtime-predicate and if the actual comparison is done between two different runtime-comparators. Note that associative containers - even though they also support this kind of runtime/dynamic comparison - are *not* sensitive to this unexpected behaviour. The simple reason is that the implementation uses an asymmetric algorithm to realize the concept. The program provided at tghe end of this posting demonstrates this kind of violation of the usual symmetric property of EqualityComparable. The output should be: s1 == s2: 1 s2 == s1: 0 I hope this comment is not understood as some form of destructive criticism. AFAIK there does not exist any general valid algorithm which can realize a pure *symmetric* unordered equality comparison with an average linear complexitity. My point is, that I strongly propose to mention this unexpected property and/or to declare code as causing undefined behaviour if it attempts to use EqualityComparable of unordered containers if the predicate is dynamic and different between the compared containers. Greetings from Bremen, Daniel #include <cctype> #include <iostream> #include <ostream> #include <boost/unordered_set.hpp> typedef boost::unordered_set<char, std::size_t(*)(char), bool (*)(char, char)> MySet; std::size_t hash_char(char c) { return static_cast<std::size_t>(c); } bool eq_char(char c1, char c2) { return c1 == c2; } std::size_t hash_char_ic(char c) { return static_cast<std::size_t>(std::tolower(c)); } bool eq_char_ic(char c1, char c2) { return std::tolower(c1) == std::tolower(c2); } int main() { MySet s1(1, hash_char, eq_char); s1.insert('A'); MySet s2(1, hash_char_ic, eq_char_ic); s2.insert('a'); bool t1 = s1 == s2; std::cout << "s1 == s2: " << t1 << std::endl; bool t2 = s2 == s1; std::cout << "s2 == s1: " << t2 << std::endl; std::cin.get(); }

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how to make fusion::pair less-than-comparable?
by Zeljko Vrba 22 Aug '08

22 Aug '08

Related to my previous question: fusion::map is a sequence and instances of it could be directly compared with operator < , thus vectors of instances also sorted if fusion::pair supported relational operators other than == and != (which it doesn't). So, two questions: 1. What is the recommended way of defining operator< for particular pair instances (e.g. for pair<net, int>) ? 2. An explanation of why doesn't fusion::pair define at least operator< would be welcome. Thanks. (Yes, I know, I can pass an explicit predicate to std::sort.. )

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Re: [Boost-users] Boost serialization..
by Sangeeta Singh 22 Aug '08

22 Aug '08

Hi, Thanks for the pointer. Is the string serialization for 64 bit and 32 bit library different as the string being serialized using 64bit version can not be read using 32 bit version. Thanks, Sangeeta Message: 1 Date: Thu, 21 Aug 2008 13:10:26 -0800 From: "Robert Ramey" <ramey(a)rrsd.com> Subject: Re: [Boost-users] Boost serialization.. To: boost-users(a)lists.boost.org Message-ID: <g8ki3p$iv7$2(a)ger.gmane.org> Content-Type: text/plain; charset="iso-8859-1" THe library includes a portable_binary archive as a demo. There are also other versions of this in boost downloads. Robert Ramey "Sangeeta Singh" <singhs(a)yahoo-inc.com> wrote in message news:228C81146E16054AA04E582D4B8C34CD96C888@SNV-EXVS08.ds.corp.yahoo.com ... Hi, I have following requirement Application doing the object serialization (binary stream with char trait) uses 64 bit boost serialization version Application deserializing the object uses 32 bit boost serialization version Both are incompatible. Is there a boost serialization library available that works for both 64 and 32 bit m/c or is there any other way that I can achieve this. Thanks, Sangeeta

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Serialization of derived classes with boost 1.34.1
by Hansi 22 Aug '08

22 Aug '08

Hello, I have a problem to serialize a derived class. In some classes I use a shared_ptr<A> which acts as a interface for some other classes. Til now I had the implementation in the header and it worked fine with the BOOST_CLASS_EXPORT(B) declaration after at the end of the header file where B was defined. For performance reason (compile time) I have moved the serialization code from the header file (there is only the declaration) to the .cpp file (now I use also only the polymorphic_binary_archive). There I have also the declaration for the polymorphic_binary_archive template void B::serialize(boost::archive::polymorphic_iarchive& ar, const unsigned int file_version); template void B::serialize(boost::archive::polymorphic_oarchive& ar, const unsigned int file_version); After linking I have now some linker errors. First for the class B which is derived from A and for the class A. All linker errors use the binary_archive. If I declare the "BOOST_CLASS_EXPORT(B)" at the end in the .cpp file I get only an linker error for class A. How I can solve this? Best regards Hansjörg

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Re: [Boost-users] Fusion: some concrete questions about maps and vectors
by Zeljko Vrba 22 Aug '08

22 Aug '08

On Thu, Aug 21, 2008 at 09:39:01PM -0400, Daryle Walker wrote: > > Are the two vectors supposed to represent the same relation? If so, > could Boost's BiMap help? > No, they represent the two halves of a symmetric relation.

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Fusion: some concrete questions about maps and vectors
by Zeljko Vrba 22 Aug '08

22 Aug '08

I'm operating on two vectors of pairs of numbers, currently represented by std::pair<unsigned, unsigned>. The first vector is a list of (net,pin) pairs, while the second vector is a list of (pin, net) pairs. In order to raise a bit the understandability / abstraction level of my code, I think that it'd be nice to be able to write at_key<pin>(x) and at_key<net>(x) instead of x.first or using tie(). Looking at fusion manual, it seems that of all the containers, map suits the purpose: struct pin; struct net; First question: are Map1 and Map2 different types? typedef map<pair<pin, unsigned>, pair<net, unsigned> > Map1; typedef map<pair<net, unsigned>, pair<pin, unsigned> > Map2; According to a simple test program that I wrote, which basically boils down to Map m1; Map m2; m1 = m2; they, are different because the compilation fails. Hmm, so far, so good. Second question: some algorithms are common both for both types, e.g. sort, where I want to have lexicographical comparison between the elements. Is it possible to somehow transform Map1 and Map2 so that they both appear as typedef vector<unsigned, unsigned> > Pair with proper lexicographical ordering? OK, there are conversion metafunctions, but I want something more; the following code std::vector<Map1> m; std::sort(m.begin(), m.end()); should process vector elements (Map1s) _as_if_ they were Pairs or ordinary std::pair. I see there are conversion metafunctions defined in documentation, but I don't know how to use them to convert std::vector<Map1> to std::vector<Pair> when giving m as argument to sort() [if this is possible at all]. Sorry for the long post and if it is somewhat vague. === (I could probably avoid using fusion by manually defining two different struct types, each holding pin/net members and defining operator< for each, but I want to finally get my hands dirty with fusion on a concrete, not too complex problem that I'm facing right now.)

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Boost-users] [python]How to pass C++ object reference to python code?
by Neil Fang 22 Aug '08

22 Aug '08

I'm trying embedding python using boost::python. Just as the same way as the boost::python quick start "embedding.cpp". I have a C++ base class, with a virtual function do something on another C++ object: struct MyClass { void printThis() { std::cout << "0x" << this << std::endl; } }; // An abstract base class class Base : public boost::noncopyable { public: virtual ~Base() {}; virtual void printMyClass(MyClass& myObj) = 0; }; Than, I want to write some Python derived class code: "from embedded_hello import * \n" "class PythonDerived(Base): \n" " def printMyClass(self, myObj): \n" " myObj.printThis() \n" But I found that the "myObj" passed to python code is another obj, not the object created in C++ code. How can use the object created in C++ object rather than a copyed object? Thanks! The full code list below, which is modified form boost::python example. // Copyright Stefan Seefeld 2005. // Distributed under the Boost Software License, Version 1.0. (See // accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) #include <boost/python.hpp> #include <boost/detail/lightweight_test.hpp> #include <iostream> namespace python = boost::python; struct MyClass { void printThis() { std::cout << "0x" << this << std::endl; } }; // An abstract base class class Base : public boost::noncopyable { public: virtual ~Base() {}; virtual std::string hello() = 0; virtual void printMyClass(MyClass& myObj) = 0; }; // C++ derived class class CppDerived : public Base { public: virtual ~CppDerived() {} virtual std::string hello() { return "Hello from C++!";} virtual void printMyClass(MyClass& myObj) { myObj.printThis(); } }; // Familiar Boost.Python wrapper class for Base struct BaseWrap : Base, python::wrapper<Base> { virtual void printMyClass(MyClass& myObj) { this->get_override("printMyClass")(myObj); } virtual std::string hello() { #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) // workaround for VC++ 6.x or 7.0, see // http://boost.org/libs/python/doc/tutorial/doc/html/python/exposing.html#pyt… return python::call<std::string>(this->get_override("hello").ptr()); #else return this->get_override("hello")(); #endif } }; // Pack the Base class wrapper into a module BOOST_PYTHON_MODULE(embedded_hello) { python::class_<BaseWrap, boost::noncopyable> base("Base"); python::class_<MyClass>("MyClass") .def("printThis", &MyClass::printThis) ; } void exec_test() { std::cout << "registering extension module embedded_hello..." << std::endl; // Register the module with the interpreter if (PyImport_AppendInittab("embedded_hello", initembedded_hello) == -1) throw std::runtime_error("Failed to add embedded_hello to the interpreter's " "builtin modules"); std::cout << "defining Python class derived from Base..." << std::endl; // Retrieve the main module python::object main = python::import("__main__"); // Retrieve the main module's namespace python::object global(main.attr("__dict__")); // Define the derived class in Python. python::object result = python::exec( "from embedded_hello import * \n" "class PythonDerived(Base): \n" " def hello(self): \n" " return 'Hello from Python!' \n" " def printMyClass(self, myObj): \n" " myObj.printThis() \n" , global, global); python::object PythonDerived = global["PythonDerived"]; MyClass myObj; // Creating and using instances of the C++ class is as easy as always. CppDerived cpp; BOOST_TEST(cpp.hello() == "Hello from C++!"); cpp.printMyClass(myObj); std::cout << "testing derived class from C++..." << std::endl; // But now creating and using instances of the Python class is almost // as easy! python::object py_base = PythonDerived(); Base& py = python::extract<Base&>(py_base) BOOST_EXTRACT_WORKAROUND; // Make sure the right 'hello' method is called. BOOST_TEST(py.hello() == "Hello from Python!"); py.printMyClass(myObj); std::cout << "success!" << std::endl; } void exec_file_test(std::string const &script) { std::cout << "running file " << script << "..." << std::endl; // Run a python script in an empty environment. python::dict global; python::object result = python::exec_file(script.c_str(), global, global); // Extract an object the script stored in the global dictionary. BOOST_TEST(python::extract<int>(global["number"]) == 42); std::cout << "success!" << std::endl; } void exec_test_error() { std::cout << "intentionally causing a python exception..." << std::endl; // Execute a statement that raises a python exception. python::dict global; python::object result = python::exec("print unknown \n", global, global); std::cout << "Oops! This statement should be skipped due to an exception" << std::endl; } int main(int argc, char **argv) { //BOOST_TEST(argc == 2); //std::string script = argv[1]; // Initialize the interpreter Py_Initialize(); bool error_expected = false; if ( python::handle_exception(exec_test) ) { if (PyErr_Occurred()) { if (!error_expected) BOOST_ERROR("Python Error detected"); PyErr_Print(); } else { BOOST_ERROR("A C++ exception was thrown for which " "there was no exception translator registered."); } } std::cin.get(); // Boost.Python doesn't support Py_Finalize yet, so don't call it! return boost::report_errors(); }

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boost.python - undefined symbol error
by antonyc 22 Aug '08

22 Aug '08

I've just started this morning with boost::python and have been struggling all day to get the basic http://www.boost.org/doc/libs/1_35_0/libs/python/doc/tutorial/doc/html/pyth… 'exposing classes' doc/tutorial: to link correctly under gcc 4.1.2. I would greatly appreciate any help as I'm sure it's probably something simple and I'm pretty much at a loss at the moment. So the source file compiles and the shared object appears to link ok however when I try and import the module, python reports the following missing symbol: ImportError: /test/BoostPython/hello.so: undefined symbol: _ZN5boost6python9converter8registry6insertEPFPvP7_objectEPFvS5_PNS1_30rvalue_from_python_stage1_dataEENS0_9type_infoE de-mangled courtesy of c++filt: boost::python::converter::registry::insert(void* (*)(_object*), void (*)(_object*, boost::python::converter::rvalue_from_python_stage1_data*), boost::python::type_info) Indeed a search through the boost.python headers yields no such function prototype. Nor does searching the symbols defined in libboost_python-gcc41-mt.so. The closest match I can find in libboost_python-gcc41-mt.so is: boost::python::converter::registry::insert(void* (*)(_object*), void (*)(_object*, boost::python::converter::rvalue_from_python_stage1_data*), boost::python::type_info, _typeobject const* (*)()) which appears to match the following function in python/converter/registry.hpp: // Insert an rvalue from_python converter BOOST_PYTHON_DECL void insert( convertible_function , constructor_function , type_info , PyTypeObject const* (*expected_pytype)() = 0 ); Beyond that I'm pretty much stuck. Thanks in advance to anyone who can help me out! antony /*------------------- hello.cpp -------------------*/ #include <string> struct World { void set(std::string msg) { this->msg = msg; } std::string greet() { return msg; } std::string msg; }; #include <boost/python.hpp> using namespace boost::python; BOOST_PYTHON_MODULE(hello) { class_<World>("World") .def("greet", &World::greet) .def("set", &World::set) ; } /*-----------------------------------------------------------*/ g++ -c -g -Wall -fPIC -pipe -DBOOST_PYTHON_MAX_ARITY=20 -I. -I/usr/local/include -I/usr/local/include/python2.5 hello.cpp g++ -shared -o hello.so hello.o -L/usr/local/lib -lpython2.5 -lboost_python-gcc41-mt -- View this message in context: http://www.nabble.com/boost.python---undefined-symbol-error-tp19054023p1905… Sent from the Boost - Users mailing list archive at Nabble.com.

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re: Wrapping a library
by Alan Baljeu 21 Aug '08

21 Aug '08

>> I have this library (one class with 700 methods) I want to wrap all the calls, so I can log the calls and do other stuff. Using emacs macros and stuff, I >>can create a proxy class which has the same signature, but each method calls a C macro which calls the original class method, and does other stuff. > A class or a namespace? A document class. Yes it's huge. >> >> I'm thinking there must be a better way. I'm thinking BOOST_PP library could abstract the above macros into something concise. However, the >> library is intimidating. There are lots of features, and I'm not clear on how I should get started. >For ad hoc code generation, I usually end up with awk and sed. I just did this wrapping >thing with a java class definition ( no actual source code) and could pretty much use lynx to render the javadoc html, extract >method signatures, and use awk to generate methods with sed and finally >vi to touch stuff up. The generated class contained an instance of the original class that >was simply called in each generated method after my custion code,if any, executed. >I wasn't just interested in wrapping as I also made a fake version for >unsupported operations. That does seem to be a good approach. Thanks for the idea. __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now at http://ca.toolbar.yahoo.com.

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Boost serialization..
by Sangeeta Singh 21 Aug '08

21 Aug '08

Hi, I have following requirement Application doing the object serialization (binary stream with char trait) uses 64 bit boost serialization version Application deserializing the object uses 32 bit boost serialization version Both are incompatible. Is there a boost serialization library available that works for both 64 and 32 bit m/c or is there any other way that I can achieve this. Thanks, Sangeeta

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