boost::filter_iterator 也为 end() 调用谓词？

Question

我正在为 boost::filter_iterator 苦苦挣扎。我用它来创建一个跳过一些元素的自定义迭代器。这些元素是一些粒子之间的接触，一些接触定义了它们的几何形状（Contact::geom）；我想跳过那些没有定义它的（即！Contact::geom）。一个缩短的版本看起来像这样（我可能无法缩短它）：

struct Contact{
    shared_ptr<CGeom> geom;
    bool isReal(){ return (bool)geom; }
    /* some other data... */
};

struct ContactContainer{

    // this is the underlying container 
    typedef vector<shared_ptr<Contact> > ContainerT;
    ContainerT data;                                  

    // predicate defining whether we skip this contact or not
    struct IsReal{
        bool operator()(shared_ptr<Contact>& c){ return c && c->isReal(); }
        bool operator()(const shared_ptr<Contact>& c){ return c && c->isReal(); }
    };

    typedef boost::filter_iterator<IsReal,ContainerT::iterator> iterator;
    typedef boost::filter_iterator<IsReal,ContainerT::const_iterator> const_iterator;

    // return proxy iterator
    iterator begin(){ return data.begin(); }
    iterator end(){ return data.end(); }
    const_iterator begin() const { return const_iterator(data.begin()); }
    const_iterator end() const { return const_iterator(data.end()); }
    size_t size() const { return data.size(); }
};

Now at one place of the code, I iterate over the ContactContainer using BOOST_FOREACH, which should filter out contacts where !c->isReal() automatically:

BOOST_FOREACH(const shared_ptr<Contact>& c, contacts){
    /* do something here */
};

我不断从调试器中得到这个：

#4  <signal handler called>
#5  0x00007fc94cdc4ad4 in boost::shared_ptr<CGeom>::operator CGeom* boost::shared_ptr<CGeom>::* (this=0x2dee04a518aa88) at /usr/include/boost/smart_ptr/detail/operator_bool.hpp:47
#6  0x00007fc94cdbefe4 in Contact::isReal (this=0x2dee04a518aa80) at /home/eudoxos/yade/build-tr2/dbg/include/yade/pkg/dem/Particle.hpp:101
#7  0x00007fc94ce2a2da in ContactContainer::IsReal::operator() (this=0x7fff1ebe1038, c=...) at pkg/dem/ContactContainer.cpp:8
#8  0x00007fc94d0a9e05 in boost::filter_iterator<ContactContainer::IsReal, __gnu_cxx::__normal_iterator<boost::shared_ptr<Contact>*, std::vector<boost::shared_ptr<Contact>, std::allocator<boost::shared_ptr<Contact> > > > >::satisfy_predicate (this=0x7fff1ebe1030) at /usr/include/boost/iterator/filter_iterator.hpp:100
#9  0x00007fc94d0a5ae7 in boost::filter_iterator<ContactContainer::IsReal, __gnu_cxx::__normal_iterator<boost::shared_ptr<Contact>*, std::vector<boost::shared_ptr<Contact>, std::allocator<boost::shared_ptr<Contact> > > > >::filter_iterator (this=0x7fff1ebe1030, x=..., end_=...) at /usr/include/boost/iterator/filter_iterator.hpp:72
#10 0x00007fc94d09b311 in ContactContainer::end (this=0x3df5b40) at /home/eudoxos/yade/build-tr2/dbg/include/yade/pkg/dem/ContactContainer.hpp:46
#11 0x00007fc94d0b098b in boost::range_detail::range_end<ContactContainer> (c=...) at /usr/include/boost/range/end.hpp:50
#12 0x00007fc94d0ace87 in boost::end<ContactContainer> (r=...) at /usr/include/boost/range/end.hpp:99
#13 0x00007fc94d0a95c1 in boost::foreach_detail_::end<ContactContainer, mpl_::bool_<false> > (col=...) at /usr/include/boost/foreach.hpp:693

如果我没看错，filter_iterator 也会在 ContactContainer::end() 上调用谓词，这实际上是 ContactContainer::data.end()。这是预期的行为吗？不幸的是，文档只显示了数字过滤，我不知道如何继续。

有人可以启发我吗？

干杯，

瓦茨拉夫

Answer 1

filter_iterator 的构造函数采用两个迭代器：begin 和 end，如

filter_iterator(Iterator x, Iterator end = Iterator());

以下更改使您的示例为我执行：

iterator begin(){ return iterator(data.begin(), data.end()); }
iterator end(){ return iterator(data.end(), data.end());}

测试运行：https://ideone.com/6qaeq