[英]How to store pointer / iterator reference to stl container element in C++?
I am designing a graph class which I want to base on an adjacency list. 我正在设计一个图形类,我想基于邻接列表。 The class internally has a DataStructure :
该类内部有一个DataStructure:
std::unordered_map<Node,std::list<??>,NodeHash,NodeEqual> map;
Instead of ??
而不是
??
, I want either pointer to Node element stored in list or some iterator pointing to it. ,我想要指向存储在列表中的Node元素的指针或指向它的一些迭代器。
I am new to C++. 我是C ++的新手。 How should I go about it?
我该怎么办呢?
How do I get pointer to an existing key node from the unordered_map?
如何从unordered_map获取指向现有关键节点的指针?
Find the element with that key, take the address of the first
member of the element. 找到具有该键的元素,获取元素的
first
成员的地址。
std::unordered_map<Node,std::list<Node*>,NodeHash,NodeEqual> map;
Node node1;
(void) map[node1]; // add { node1, {} } to the map
...
auto iter = map.find(node1);
if (iter != map.end())
{
Node* n = &iter->first;
Node node2;
map[node2].push_back(n);
}
Here n
is a pointer to the existing key that is equal to node1
. 这里
n
是指向等于node1
的现有键的指针。
This works in with ideone
; 这适用于
ideone
; I don't know if it's portable. 我不知道它是否便携。
struct M;
typedef std::unordered_map<Node, std::list<M>, NodeHash, NodeEqual> mymap;
struct M { mymap::iterator x; };
Unfortunately, M
isn't quite an iterator to mymap
, but it's pretty close. 不幸的是,
M
是不是很给迭代器mymap
,但它是相当接近。
( ideone
complains if I try the same trick to make M
a wrapper of std::list<mymap::iterator>
instead) (如果我尝试使用相同的技巧使
M
成为std::list<mymap::iterator>
的包装,那么ideone
抱怨)
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