[bidirectional.iterators] (original) (raw)
24 Iterators library [iterators]
24.3 Iterator requirements [iterator.requirements]
24.3.5 C++17 iterator requirements [iterator.cpp17]
24.3.5.6 Bidirectional iterators [bidirectional.iterators]
A class or pointer typeXmeets the requirements of a bidirectional iterator if, in addition to meeting the Cpp17ForwardIterator requirements, the following expressions are valid as shown in Table 80.
Table 80 — Cpp17BidirectionalIterator requirements (in addition to Cpp17ForwardIterator) [tab:bidirectionaliterator]
| 🔗Expression | Return type | Operational | Assertion/note |
|---|---|---|---|
| 🔗 | semantics | pre-/post-condition | |
| 🔗--r | X& | Preconditions: there exists s such that r == ++s. Postconditions: r is dereferenceable. --(++r) == r. --r == --s implies r == s. addressof(r) == addressof(--r). | |
| 🔗r-- | convertible to const X& | { X tmp = r; --r; return tmp; } | |
| 🔗*r-- | reference |
[Note 1:
Bidirectional iterators allow algorithms to move iterators backward as well as forward.
— _end note_]