[英]C++ iterator to const_iterator
How do I acquire a const_iterator
(of some container class) from an iterator
(of that container class) in C++?如何从 C++ 中的
iterator
(该容器类的)获取const_iterator
(某个容器类的)? What about a const_iterator
from an insert_iterator
?来自
insert_iterator
的const_iterator
怎么样? The resulting iterator
should point at the same spot as the original does.生成的
iterator
应该指向与原始iterator
相同的位置。
Containers are required to provide iterator
as a type convertible to const_iterator
, so you can convert implicitly:容器需要提供
iterator
作为可转换为const_iterator
的类型,因此您可以隐式转换:
Container::iterator it = /* blah */;
Container::const_iterator cit = it;
std::insert_iterator
s are output iterators. std::insert_iterator
是输出迭代器。 This gives no way to convert them to a regular Container::iterator
which must be a forward iterator.这无法将它们转换为必须是前向迭代器的常规
Container::iterator
iterator。
Another kind of insert iterator may allow such a thing, but those obtained from the standard functions don't.另一种插入迭代器可能允许这样的事情,但那些从标准函数中获得的则不允许。
I guess you can write your own wrapper around std::insert_iterator
that exposes the protected member iter
, though:我想您可以围绕
std::insert_iterator
编写自己的包装器,以公开受保护的成员iter
,不过:
template <typename Container>
class exposing_insert_iterator : public std::insert_iterator<Container> {
public:
exposing_insert_iterator(std::insert_iterator<Container> it)
: std::insert_iterator<Container>(it) {}
typename Container::iterator get_iterator() const {
return std::insert_iterator<Container>::iter;
}
};
// ...
std::insert_iterator<Container> ins_it;
exposing_insert_iterator<Container> exp_it = ins_it;
Container::iterator it = exp_it.get_iterator();
You can convert them.你可以转换它们。 Example:
例子:
std::vector<int> v;
std::vector<int>::iterator it = v.begin();
std::vector<int>::const_iterator cit = it;
But I guess that is not the answer you are seeking.但我想这不是你想要的答案。 Show me code.
给我看代码。 :-)
:-)
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