[英]wrap std::iterator in C++
I have a need to wrap a vector iterator, but don't like the idea to rewrite it from scratch. 我需要包装一个矢量迭代器,但不喜欢从头开始重写它的想法。 And I can't subclass it as far as vector iterator doesn't seem to be cross-platform.
而且我不能将它子类化,因为矢量迭代器似乎不是跨平台的。 At least gnu and ibm ones look different.
至少gnu和ibm看起来不同。
What I want to do is the following: 我想做的是以下内容:
class MyContainer {
vector<double> data;
vector<int> indices;
iterator
begin()
{ return my_iterator(data, indices.begin()); }
iterator
end()
{ return my_iterator(data, indices.end()); }
}
MyContainer cont;
Where indices vector contains integer positions within the data vector. 其中索引向量包含数据向量内的整数位置。 Data is supposed to be much much bigger than the indices.
数据应该比指数大得多。
So I need an iterator that can go through the indices in any direction like a normal vector iterator does with the only exception: it must return a value of data vector when the value is going to be accessed. 所以我需要一个迭代器,它可以在任何方向上遍历索引,就像普通的向量迭代器那样唯一的例外:当要访问该值时,它必须返回数据向量的值。 eg:
例如:
for(MyContainer::iterator it = cont.begin(); it != cont.end(); it++) {
cout << *it << endl; // values of data should appear here
}
Basically it should look like a normal collection for the std world. 基本上它应该看起来像std世界的正常集合。 You can iterate it in whatever direction you want, you can sort it, run unique, find_if, etc...
你可以在任何你想要的方向迭代它,你可以对它进行排序,运行唯一,find_if等...
any simple solution? 任何简单的方案?
There's a great Boost library for defining custom iterators. 有一个很棒的Boost库用于定义自定义迭代器。 You need to provide a class with a few methods:
您需要提供一些具有几种方法的类:
i.dereference() Access the value referred to
i.equal(j) Compare for equality with j
i.increment() Advance by one position
i.decrement() Retreat by one position
i.advance(n) Advance by n positions
i.distance_to(j) Measure the distance to j
Then you get the rest from the iterator_facade . 然后你从iterator_facade得到其余的。
Good luck! 祝好运!
This looks a lot like a permutation_iterator , one of the "built in" adapters from the Boost.Iterator Library 这看起来很像permutation_iterator ,它是Boost.Iterator库中的“内置”适配器之一
See this example (modified from the Boost docs) on codepad. 在键盘上查看此示例 (从Boost文档修改)。
There's nothing in the standard C++ library, but you can probably get boost::iterator_adapter
to do what you want. 标准C ++库中没有任何内容,但您可以使用
boost::iterator_adapter
来执行您想要的操作。 A preliminary examination suggests you'll need to override iterator_adapter::dereference
and iterator_adapter::equal
. 初步检查表明你需要覆盖
iterator_adapter::dereference
和iterator_adapter::equal
。
template <typename _Scalar=double,
typename _Idx=int,
typename _Seq=std::vector<_Scalar>,
typename _IdxVector=std::vector<_Idx> >
class SelIter
: public boost::iterator_adaptor< SelIter<_Scalar, _Idx>,
typename _IdxVector::iterator, _Scalar >
{
public:
typedef boost::iterator_adaptor< SelIter, typename _IdxVector::iterator, _Scalar > Base;
SelIter(_Seq& scalars, _IdxVector& idxs);
SelIter(_Seq& scalars, typename _IdxVector::iterator pi);
typename Base::reference dereference() const;
bool equal(const SelIter& x) const;
private:
// ...
}
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