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| Category: iterators | | Component type: concept |
Description
A Bidirectional Iterator is an iterator that can be both incremented and decremented. The requirement that a Bidirectional Iterator can be decremented is the only thing that distinguishes Bidirectional Iterators from ForwardIterator.
Refinement of
ForwardIterator
Associated types
The same as for ForwardIterator.
Notation
X | A type that is a model of Bidirectional Iterator |
T | The value type of X |
i, j | Object of type X |
t | Object of type T |
Definitions
Valid expressions
In addition to the expressions defined in ForwardIterator, the following expressions must be valid.
| Name | Expression | Type requirements | Return type |
| Predecrement | --i | | X& |
| Postdecrement | i-- | | X |
Expression Semantics
Semantics of an expression is defined only where it is not defined in ForwardIterator.
| Name | Expression | Precondition | Semantics | Postcondition |
| Predecrement | --i | i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j. | i is modified to point to the previous element. | i is dereferenceable. &i = &--i. If i == j, then --i == --j. If j is dereferenceable and i == ++j, then --i == j. |
| Postdecrement | i-- | i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j. | Equivalent to {
X tmp = i;
--i;
return tmp;
}
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Complexity guarantees
The complexity of operations on bidirectional iterators is guaranteed to be amortized constant time.
Invariants
| Symmetry of increment and decrement | If i is dereferenceable, then ++i; --i; is a null operation. Similarly, --i; ++i; is a null operation. |
Models
Notes
See also
InputIterator, OutputIterator, ForwardIterator, RandomAccessIterator, Iterators
