Defined in header `<iterator>` | ||
---|---|---|

template <class I, class T> concept output_iterator = std::input_or_output_iterator<I> && std::indirectly_writable<I, T> && requires(I i, T&& t) { *i++ = std::forward<T>(t); // not required to be equality-preserving }; | (since C++20) |

The `output_iterator`

concept is a refinement of `input_or_output_iterator`

, adding the requirement that it can be used to write values of type and value category encoded by `T`

(via `indirectly_writable`

). `equality_comparable`

is not required.

Let `E`

be an expression such that `decltype((E))`

is `T`

, and `i`

be a dereferenceable object of type `I`

. `output_iterator<I, T>`

is modeled only if all the concepts it subsumes are modeled, and `*i++ = E;`

has effects equivalent to `*i = E; ++i;`

.

An expression is *equality preserving* if it results in equal outputs given equal inputs.

- The inputs to an expression consist of its operands.
- The outputs of an expression consist of its result and all operands modified by the expression (if any).

In specification of standard concepts, operands are defined as the largest subexpressions that include only:

- an id-expression, and
- invocations of
`std::move`

,`std::forward`

, and`std::declval`

.

The cv-qualification and value category of each operand is determined by assuming that each template type parameter denotes a cv-unqualified complete non-array object type.

Every expression required to be equality preserving is further required to be *stable*: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.

Unlike the LegacyOutputIterator requirements, the `output_iterator`

concept does not require that the iterator category tag be defined.

Algorithms on output iterators should be single pass.

(C++20) | specifies that objects of a type can be incremented and dereferenced (concept) |

© cppreference.com

Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.

https://en.cppreference.com/w/cpp/iterator/output_iterator