September 2008 - Boost-users

Merging sorted iterators?
by Dr. Roland Bock 17 Sep '08

17 Sep '08

Hi, I have a bunch of iterators over some sorted input from several big files which do not fit into memory. What I would like to have is one iterator which allows me to iterate over the combined sorted input (of course, the result should be sorted, too). Something like this: -------\ --------\ ... ---- --------/ -------/ Is there a class in boost which allows me to do this in a simple way? Thanks and regards, Roland

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[filesystem] Strange problems on Cygwin with 1.36.0
by Boris 17 Sep '08

17 Sep '08

According to http://www.boost.org/doc/libs/1_36_0/libs/filesystem/doc/index.htm#Cgywin Boost.Filesystem seems to be supported on Cygwin. However with the latest version 1.36.0 (which I've built with BOOST_POSIX_API defined) I don't seem to get any Boost.Filesystem function to work on Cygwin. I'm currently running some test cases and had to modify them for Cygwin like this: #if defined(__CYGWIN__) BOOST_CHECK(a == b); #else BOOST_CHECK(bfs::equivalent(a, b)); #endif If a and b contain the very same path you would expect both a == b and boost::filesystem::equivalent() to return true. However on Cygwin boost::filesystem::equivalent() returns false. If I use BOOST_CHECK(bfs::equivalent(a, b)) on Cygwin I get this error: unknown location(0): fatal error in "test_find_param": std::runtime_error: boost::filesystem::equivalent: No such file or directory: "\home\Boris\boost_1_36_0\libs\process\test\..\..\..\bin.v2\libs\process\test\gcc-3.4.4\debug\link-static\runtime-link-static\helpers.exe", "\home\Boris\boost_1_36_0\libs\process\test\..\..\..\bin.v2\libs\process\test\gcc-3.4.4\debug\link-static\runtime-link-static\helpers.exe" Both strings are exactly the same and contain valid Cygwin paths. Is Boost.Filesystem broken on Cygwin? Boris PS: I've a similar problem with boost::filesystem::create_directory() which can't create a directory for no obvious reason.

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[smart_ptr] Problem with circular reference detection
by Jim Barry 17 Sep '08

17 Sep '08

I am trying to detect circular references using the find_unreachable_objects function in sp_collector.cpp. However, it reports false positives in the simple case of one object being owned by another. To illustrate: #define BOOST_SP_ENABLE_DEBUG_HOOKS #include <boost/shared_ptr.hpp> // sp_collector.cpp exported functions std::size_t find_unreachable_objects(bool report); struct X {}; struct Y { boost::shared_ptr<X> pX; Y() : pX(new X) {} }; int main() { boost::shared_ptr<Y> y(new Y); find_unreachable_objects(true); return 0; } The output is as follows: ... 2 objects in m. ... 1 objects in m2. ... 1 objects in open. Unreachable object at 0036BA60, 12 bytes long. Clearly this is incorrect as there are no circular references. Looking at the code, there is what appears to be a typo at line 124: std::cout << "... " << m2.size() << " objects in open.\n"; should be: std::cout << "... " << open.size() << " objects in open.\n"; But the real problem seems to be at line 121: if(p->use_count() != i->second) open.push_back(p); I'm not entirely sure what's going on in this section of code, but it ends up determining (incorrectly) that the "X" object is unreachable. Is there any way to get this working properly? Thanks, - Jim

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Boost Serialize and derived classes
by John Yamokoski 17 Sep '08

17 Sep '08

I can't seem to figure out if what I want is possible. I am using the Boost Serialization library to save the state of my program. I have a manager-type class which holds onto pointers of a base class. The Boost Serialization website has a lot to say about base and derived classes. In a tutorial they show one way to deal with them. But it assumes a priori knowledge of the derived classes: class bus_route { friend class boost::serialization::access; friend std::ostream & operator<<(std::ostream &os, const bus_route &br); typedef bus_stop * bus_stop_pointer; std::list<bus_stop_pointer> stops; template<class Archive> void serialize(Archive &ar, const unsigned int version) { // in this program, these classes are never serialized directly but rather // through a pointer to the base class bus_stop. So we need a way to be // sure that the archive contains information about these derived classes. //ar.template register_type<bus_stop_corner>(); ar.register_type(static_cast<bus_stop_corner *>(NULL)); // TYPES KNOWN A PRIORI //ar.template register_type<bus_stop_destination>(); ar.register_type(static_cast<bus_stop_destination *>(NULL)); // TYPES KNOWN A PRIORI // serialization of stl collections is already defined // in the header ar & BOOST_SERIALIZATION_NVP(stops); } public: bus_route(){} void append(bus_stop *_bs) { stops.insert(stops.end(), _bs); } }; In my code, however, I don't know exactly what the derived classes might be. The derived objects are created and passed back to my manager class through the base pointer. One option I was considering was that when plugins register with the program, they would have to also register the derived class names with the archive. How this would actually be implemented, I have no idea. Can an archive object be created independently from the Serialization library, modified and then sent back to Serialization? Here is a simple test case I am working on, but I just can't get it to write out the derived classes to file: class base { friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int file_version) { ar & BOOST_SERIALIZATION_NVP(val); } public: base() : val(0.0) {} base(double b) : val(b) {} double val; }; class derived : public base { friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int file_version) { boost::serialization::void_cast_register<derived, base>(static_cast<derived *>(NULL),static_cast<base *>(NULL)); ar & BOOST_SERIALIZATION_NVP(val); } public: derived() : base(0.0), val(0) {} derived(int a, double b) : base(b), val(a) {} int val; }; BOOST_CLASS_EXPORT_GUID(derived, "derived"); class manager { friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int file_version) { ar & BOOST_SERIALIZATION_NVP(objs); } public: std::list<base*> objs; }; void main() { manager mgr; // Creat some data to save derived *d1, *d2, *d3, *d4; d1 = new derived(1, 1.0); d2 = new derived(2, 3.0); mgr.objs.push_back( d1 ); mgr.objs.push_back( d2 ); { std::ofstream ofs("out.xml"); assert(ofs.good()); boost::archive::xml_oarchive oa(ofs); oa << BOOST_SERIALIZATION_NVP(mgr); ofs.close(); } manager new_mgr; { std::ifstream ifs("out.xml"); assert(ifs.good()); boost::archive::xml_iarchive ia(ifs); ia >> BOOST_SERIALIZATION_NVP(new_mgr); ifs.close(); } { std::ofstream ofs("check.xml"); assert(ofs.good()); boost::archive::xml_oarchive oa(ofs); oa << BOOST_SERIALIZATION_NVP(new_mgr); ofs.close(); } delete d1, d2; } I apologize if this commonly asked but I was just looking for some insight as to the best approach. J.D.

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How to implement a reader-writer lock with quick response to writer?
by Bill David 17 Sep '08

17 Sep '08

Question: How to implement a reader-writer lock with quick response to writer? I am using boost1.35.0. I know 1.36.0 is available, but I failed to build regex in 1.36.0 with VC8. I have the following requirements: 1.There are several reader threads and a single writer thread. The writer thread will update shared data periodically. And reader threads may read shared data at any time. 2.As long as writer thread try to update data, all reader thread should be blocked as soon as possible. 3.And reader thread should be blocked during data updating. 4.But reader threads can't be interrupted when they are reading. (i.e. all upcoming reader threads should be blocked, but writer still need wait till the last reader thread in reading finished.) How to implement above scenario with quick response to writer thread? I tried to write the following program to test shared_mutex, but it seems it can't meet my requirement: #include <iostream> using namespace std; #include <boost/thread/shared_mutex.hpp> #include <boost/thread/thread.hpp> #include <boost/thread/xtime.hpp> using namespace boost; boost::shared_mutex rw_mutex; int g_i = 1; void sleep(int iSec) { boost::xtime xt; boost::xtime_get(&xt, boost::TIME_UTC); xt.sec += iSec; boost::thread::sleep(xt); } void read() { while (true) { rw_mutex.lock_shared(); cout << g_i << endl; sleep(3); rw_mutex.unlock_shared(); } } int main() { boost::thread_group threads; for (int i = 0; i < 3; i++) threads.create_thread(read); sleep(1); rw_mutex.lock(); cout << "lock" << endl; g_i = 2; cout << "update g_i to " << g_i << endl; sleep(5); cout << "unlock" << endl; rw_mutex.unlock(); threads.join_all(); } The problem to above solution is it can't respond to writer thread as soon as possible, and only in rare case, it can respond to writer thread in about 6 seconds. The following is a possible output I have gotten: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 lock update g_i to 2 unlock 222 2 2 2 The writer thread should wait no more than 6 seconds, but it seems it can wait more than 20 seconds. Can shared_mutex meet such kind of scenario? If not, do you have any other suggestion?

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Problem serializing unsigned int via save/load
by Diane 16 Sep '08

16 Sep '08

Is there a trick or known bug with serializing an unsigned int via the split free functions? I have a structure that contains an unsigned int, and if I serialize with the free serialize function it works as it should. However, if I split the serialization into save/load I get: boost_1_36_0/boost/archive/detail/iserializer.hpp:541: error: conversion from `boost::serialization::is_wrapper<unsigned int>' to non-scalar type `mpl_::bool_< true>' requested Here's my structure and the two pieces of serialization code: typedef struct CCSTRUCT { unsigned int numRtp; } CCSTRUCT; Serialization #1 (works): template<class Archive> void serialize(Archive & ar, CCSTRUCT& it, const unsigned int version) { ar & it.numRtp; } Serialization #2 (doesn't work): BOOST_SERIALIZATION_SPLIT_FREE(CCSTRUCT) template<class Archive> void save(Archive & ar, const CCSTRUCT& d, unsigned int /* version */) { ar << d.numRtp; } template<class Archive> void load(Archive & ar, const CCSTRUCT& d, unsigned int /* version */) { ar >> d.numRtp; } I need to split the serialization because there are other elements in the structure that can't be handled in serialize(), so I would really appreciate some help if anyone has any ideas. Thanks, Diane

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boost::signal performance in boost 1.36 and VS2005
by Hansi 16 Sep '08

16 Sep '08

Hello, I have made now a small test and I don't know if I make something wrong. I have the following performance comparsion between a boost::function and a boost::signal. Okay, I know that boost::signal has a lot of more functionality and for that it is for sure slower than boost::function. But 100times slower? May be I do something wrong? On my pc I have for boost::function a runtime of 728ms and for boost::signals a runtime of 64128ms There is one slot used for signals. Can anyone give me some hint what I do wrong? my test program was: class TestBind { public: int counter; void OnEventReceived(char b) { counter++; } }; class TestSignal { public: int counter; void OnEventReceived(char b) { counter++; } }; int _tmain(int argc, _TCHAR* argv[]) { TestBind testBind; PerformanceCounter timer; boost::function<void (char)> f = boost::bind(&TestBind::OnEventReceived,&testBind,_1); for(int i = 0; i < 100000000; i++) { f('a'); } TestSignal testSignal; boost::signal<void (char)> sig; sig.connect(boost::bind(&TestSignal::OnEventReceived,&testSignal,_1));; for(int i = 0; i < 100000000; i++) { sig('a'); } } Best regards Hansjörg

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[serialization] Crashes after termination of main()
by Ruediger Berlich 16 Sep '08

16 Sep '08

Hi there, I am consistenty getting crashes in line 80 of the file /opt/boost136/include/boost-1_36/boost/serialization/extended_type_info_typeid.hpp , when my program exits. This is the destructor of class extended_type_info_typeid : ~extended_type_info_typeid(){ type_unregister(); } Any idea of what this is ? I'm using several singletons in my program, which according to their nature, only terminate once main() has finished. They refer to several objects which can, in other contexts, also be serialized. This specific program, however, does not make use of this option. I am pretty sure that the singletons do not refer to each other (any more) as, while searching for the problem, I have redesigned larger portions so that they don't. I'm using Boost 1.36 on OpenSUSE 11 / 64 bit (g++ 4.3.1). Thanks in any case and best regards, Ruediger

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overloading on keyword signature
by e r 16 Sep '08

16 Sep '08

hi, i'm following up on an earlier of my posts with a simpler example. in the example below: the overload is on argument-name and type, yet the overload is ambiguous. 1) is there a way around this? and if so, 2) is it also possible to have an overload the on argument-name only (replace string and int below by *). thanks. *.hpp namespace lib{ BOOST_PARAMETER_NAME(name) BOOST_PARAMETER_NAME(index) BOOST_PARAMETER_FUNCTION( (void), f, tag, (required (name,(std::string))) ) { std::cout << name << std::endl; } BOOST_PARAMETER_FUNCTION( (void), f, tag, (required (index,(int))) ) { std::cout << index << std::endl; } } *.cpp lib::f(lib::_name = "jill"); lib::f(lib::_index = 1); /home/er/cpp/libs/testing_names/par_fun.hpp||In function ‘typename lib::boost_param_result_27f<typename boost::parameter::aux::argument_pack<lib::boost_param_params_27f<int>, const ParameterArgumentType0, boost::parameter::void_, boost::parameter::void_, boost::parameter::void_, boost::parameter::void_>::type>::type lib::f(const ParameterArgumentType0&, typename boost::parameter::aux::match<lib::boost_param_params_27f<int>, ParameterArgumentType0, boost::parameter::void_, boost::parameter::void_, boost::parameter::void_, boost::parameter::void_>::type) [with ParameterArgumentType0 = boost::parameter::aux::tagged_argument<lib::tag::index, const int>]’:| /home/er/cpp/libs/testing_names/main.cpp|28|instantiated from here| /home/er/cpp/libs/testing_names/par_fun.hpp|24|error: call of overloaded ‘boost_param_implf(boost::parameter::aux::arg_list<const boost::parameter::aux::tagged_argument<lib::tag::index, const int>, boost::parameter::aux::empty_arg_list>)’ is ambiguous| /home/er/cpp/libs/testing_names/par_fun.hpp|16|note: candidates are: typename lib::boost_param_result_19f<Args>::type lib::boost_param_implf(const Args&) [with Args = boost::parameter::aux::arg_list<const boost::parameter::aux::tagged_argument<lib::tag::index, const int>, boost::parameter::aux::empty_arg_list>]| /home/er/cpp/libs/testing_names/par_fun.hpp|24|note: typename lib::boost_param_result_27f<Args>::type lib::boost_param_implf(const Args&) [with Args = boost::parameter::aux::arg_list<const boost::parameter::aux::tagged_argument<lib::tag::index, const int>, boost::parameter::aux::empty_arg_list>]| /home/er/cpp/libs/testing_names/par_fun.hpp|24|error: return-statement with a value, in function returning 'void'| ||=== Build finished: 2 errors, 0 warnings ===|

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for_each on boost::ptr_map
by Robert Dailey 16 Sep '08

16 Sep '08

Hi, Is there a way I can use std::for_each() on a boost::ptr_map and have the functor object be given the *value* of each item iterated instead of a key/value pair like it does with std::map? Help is appreciated, thank you.

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