Can I always substitute regular pointers for input iterators?

Question

Can I always substitite pointers for InputIterators in the fashion examplified in the below code?

int a[] = {5, 6, 7, 8, 9, 10};
std::list<int> l(a, a + 4); // 5, 6, 7, 8

The constructor declaration for list is (leaving out the allocator part)

list (InputIterator first, InputIterator last);

But from the C++ reference it almost seems like anything which supports actions such as ++ (increment) and * (dereferenceing) could be used as InputIterators?

Thank you.

possible duplicate of [How are iterators and pointers related?](http://stackoverflow.com/questions/2728190/how-are-iterators-and-pointers-related) — R Sahu, Sep 19 '14 at 20:50

quantdev · Accepted Answer · 2014-09-19T20:45:01.593

6

C++ Standard section § 24.2.1 [iterator.requirements.general] :

Iterators are a generalization of pointers that allow a C ++ program to work with different data structures (containers) in a uniform manner.

[...]

Since iterators are an abstraction of pointers, their semantics is a generalization of most of the semantics of pointers in C ++ . This ensures that every function template that takes iterators works as well with regular pointers.

So yes, any function template that expects an iterator (as defined in the standard) is required to work when called with regular pointers.

In particular, pointers respects all the requirements of any standard C++ iterator class (including Input Iterators)

edited Sep 19 '14 at 20:45

answered Sep 19 '14 at 20:39

quantdev

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ok, you beat me to it. 24.4.1/3 is relevant: the specialization `template iterator_traits` – rici Sep 19 '14 at 20:43
I see, I'm going to think a bit more about. Thank you! – jensa Sep 19 '14 at 20:47
1

@quantdev : I read your comment before you removed it =) thanks! – jensa Sep 19 '14 at 20:53

score 3 · Answer 2 · answered Sep 19 '14 at 20:44

Yes, you can. Iterator categories form a hierarchy. With each level including the level above (or below, depending on how you write it).

Forward iterators satisfy all the requirements of Input iterators, and then some. Bidirectional iterators support all the requirements of forward iterators, and then some. And finally, random access iterators, the most capable iterators of all, satisfy all the requirements of bidirectional iterators, and then some.

Pointers are random access iterators, therefore, they satisfy all the requirements of input iterators.

Can I always substitute regular pointers for input iterators?

2 Answers2