我正在使用boost :: filter_iterator。我用它来创建一个跳过一些元素的自定义迭代器。这些元素是某些粒子之间的接触,有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人(即!Contact :: geom)。缩短版本看起来像这样(我可能无法缩短版本):
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 */
};
我一直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
如果我正确读取它,filter_iterator也会在ContactContainer :: end()上调用谓词,它实际上是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,我对如何继续进行了处理。
有人可以启发我吗?
干杯,
瓦茨拉夫
答案 0 :(得分:2)
filter_iterator
的构造函数需要两个迭代器: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());}