A class or built-in type X models the Random Access Traversal concept if the following expressions are valid and respect the stated semantics. In the table below, Distance is iterator_traits<X>::difference_type and n represents a constant object of type Distance.
| Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal) | |||
|---|---|---|---|
| Expression | Return Type | Operational Semantics | Assertion/ Precondition |
| r += n | X& |
{
Distance m = n;
if (m >= 0)
while (m--)
++r;
else
while (m++)
--r;
return r;
}
|
|
| a + n, n + a | X | { X tmp = a; return tmp += n; } | |
| r -= n | X& | return r += -n | |
| a - n | X | { X tmp = a; return tmp -= n; } | |
| b - a | Distance | a < b ? distance(a,b) : -distance(b,a) | pre: there exists a value n of Distance such that a + n == b. b == a + (b - a). |
| a[n] | convertible to T | *(a + n) | pre: a is a Readable Iterator |
| a[n] = v | convertible to T | *(a + n) = v | pre: a is a Writable iterator |
| a < b | convertible to bool | b - a > 0 | < is a total ordering relation |
| a > b | convertible to bool | b < a | > is a total ordering relation |
| a >= b | convertible to bool | !(a < b) | |
| a <= b | convertible to bool | !(a > b) | |
| iterator_traversal<X>::type | Convertible to random_access_traversal_tag | ||