迭代器是否分配诸如指针之类的内存？

Question

Do the iterators allocate memory such as pointers?

for example:

vector<int>v(100);
vector<int>::iterator it = v.begin();

Does "it" allocate memory and store the address of the first element of vector 'v' in it? if so why can't we print the address of 'it' such as pointers?

Answer 1

Iterators are defined by the function they perform. How they perform that function is a private implementation detail. If an iterator wants to store an address, it can store an address. If it thinks storing the answer to the ultimate question of life, the universe, and everything is useful, it can store 42 somewhere. If it wants to allocate 2MB of memory, it can – but end users are likely to notice and complain. The point is that implementation details are not standardized, and all you can expect from an iterator is a reasonably efficient implementation of its functionality.

You cannot print an implementation detail because that is not part of the required functionality. (This is a good thing. The fewer requirements on the iterator, the more freedom an implementation has to make the iterator efficient.)

If you think the implementation details are critical for your application, you probably want to write your own container and iterator classes so that you are not at the mercy of your library's implementors.

If you are just looking for a debugging aid, you are asking the wrong question. It is fairly simple to get the address of the object to which an iterator points, assuming it does actually point to an object. Dereference to get the object, then take the address. (The iterator it points to the object whose address is &(*it) .) No need to obsess over implementation details.

Answer 2

There is no dynamic allocation here:

vector<int>::iterator it = v.begin();

You can think of assigning to a pointer. Iterator is not a pointer though to be exact.