`<iterator>`

Artikel
12/21/2022

Defines predefined iterators and stream iterators, iterator primitives, and supporting templates.

Requirements

Header: <iterator>

Namespace: std

Remarks

Iterators are a generalization of pointers that allow a C++ program to work with different data structures in a uniform way. Instead of operating on specific data types, algorithms operate on a range of values as specified by a kind of iterator. Algorithms can operate on any data structure that satisfies the requirements of the iterator.

In C++20, there are six categories of iterators. Iterators are arranged in a hierarchy of capability. Their capabilities are specified by C++20 concepts. For a description of the various iterators and their capabilities, see Iterator concepts

Visual Studio has added extensions to C++ Standard Library iterators to support debugging for checked and unchecked iterators. For more information, see Safe Libraries: C++ Standard Library.

Members

Functions

Name	Description
`advance`	Increments an iterator by a specified number of positions.
`back_inserter`	Creates an iterator that can insert elements at the back of a specified container.
`begin`	Retrieves an iterator to the first element in a specified container.
`cbegin`	Retrieves a read-only iterator to the first element in a specified container.
`cend`	Retrieves a read-only iterator to the element that follows the last element in the specified container.
`crbegin`	Get a reverse read-only iterator to the beginning of the specified container.
`crend`	Get the sentinel at the end of what `crbegin()` returns.
`data`	Get a pointer to the first element in the specified container.
`distance`	Determines the number of increments between the positions addressed by two iterators.
`end`	Retrieves an iterator to the element that follows the last element in the specified container.
`empty`	Test if the specified container is empty.
`front_inserter`	Creates an iterator that can insert elements at the front of a specified container.
`inserter`	An iterator adaptor that adds a new element to a container at a specified point of insertion.
`make_checked_array_iterator`	Creates a `checked_array_iterator` that can be used by other algorithms. Note: This function is a Microsoft extension of the C++ Standard Library. Code implemented by using this function isn't portable to C++ Standard build environments that don't support this Microsoft extension.
`make_move_iterator`	Returns a move iterator containing the provided iterator as its stored base iterator.
`make_unchecked_array_iterator`	Creates an `unchecked_array_iterator` that can be used by other algorithms. Note: This function is a Microsoft extension of the C++ Standard Library. Code implemented by using this function isn't portable to C++ Standard build environments that don't support this Microsoft extension.
`next`	Iterates a specified number of times and returns the new iterator position.
`prev`	Iterates in reverse a specified number of times and returns the new iterator position.
`rbegin`	Get a reverse iterator to the beginning of the specified container.
`rend`	Get a reverse iterator to the sentinel at the end of the specified container.
`size`	Get the number of elements.

Operators

Name	Description
`operator!=`	Tests if the iterator object on the left side of the operator isn't equal to the iterator object on the right side.
`operator==`	Tests if the iterator object on the left side of the operator is equal to the iterator object on the right side.
`operator<`	Tests if the iterator object on the left side of the operator is less than the iterator object on the right side.
`operator<=`	Tests if the iterator object on the left side of the operator is less than or equal to the iterator object on the right side.
`operator>`	Tests if the iterator object on the left side of the operator is greater than the iterator object on the right side.
`operator>=`	Tests if the iterator object on the left side of the operator is greater than or equal to the iterator object on the right side.
`operator+`	Adds an offset to an iterator and returns the new `reverse_iterator` addressing the inserted element at the new offset position.
`operator-`	Subtracts one iterator from another and returns the difference.

Classes

Name	Description
`back_insert_iterator`	The class template describes an output iterator object. It inserts elements into a container of type `Container`, which it accesses through the protected `pointer` object it stores called container.
`bidirectional_iterator_tag`	A class that provides a return type for an `iterator_category` function that represents a bidirectional iterator.
`checked_array_iterator`	A class that accesses an array using a random access, checked iterator. Note: This class is a Microsoft extension of the C++ Standard Library. Code implemented by using this function isn't portable to C++ Standard build environments that don't support this Microsoft extension.
`forward_iterator_tag`	A class that provides a return type for an `iterator_category` function that represents a forward iterator.
`front_insert_iterator`	The class template describes an output iterator object. It inserts elements into a container of type `Container`, which it accesses through the protected `pointer` object it stores called container.
`input_iterator_tag`	A class that provides a return type for an `iterator_category` function that represents an input iterator.
`insert_iterator`	The class template describes an output iterator object. It inserts elements into a container of type `Container`, which it accesses through the protected `pointer` object it stores called container. It also stores the protected `iterator` object, of class `Container::iterator`, called `iter`.
`istream_iterator`	The class template describes an input iterator object. It extracts objects of class `Ty` from an input stream, which it accesses through an object it stores, of type pointer to `basic_istream<Elem, Tr>`.
`istreambuf_iterator`	The class template describes an input iterator object. It inserts elements of class `Elem` into an output stream buffer, which it accesses through an object it stores, of type `pointer` to `basic_streambuf<Elem, Tr>`.
`iterator`	The class template is used as a base type for all iterators.
`iterator_traits`	A template helper class providing critical types that are associated with different iterator types so that they can be referred to in the same way.
`move_iterator`	A `move_iterator` object stores a random-access iterator of type `RandomIterator`. It behaves like a random-access iterator, except when dereferenced. The result of `operator*` is implicitly cast to `value_type&&:` to make an `rvalue reference`.
`ostream_iterator`	The class template describes an output iterator object. It inserts objects of class `Type` into an output stream, which it accesses through an object it stores, of type `pointer` to `basic_ostream<Elem, Tr>`.
`ostreambuf_iterator`	The class template describes an output iterator object. It inserts elements of class `Elem` into an output stream buffer, which it accesses through an object it stores, of type pointer to `basic_streambuf<Elem, Tr>`.
`output_iterator_tag`	A class that provides a return type for `iterator_category` function that represents an output iterator.
`random_access_iterator_tag`	A class that provides a return type for `iterator_category` function that represents a random-access iterator.
`reverse_iterator`	The class template describes an object that behaves like a random-access iterator, only in reverse.
`unchecked_array_iterator`	A class that accesses an array using a random access, unchecked iterator. Note: This class is a Microsoft extension of the C++ Standard Library. Code implemented by using this function isn't portable to C++ Standard build environments that don't support this Microsoft extension.

Concepts

The following concepts are defined in the std namespace. They apply to iterators, and are also related to the iterator categories for ranges described in <ranges> concepts.

Iterator concept	Description
`bidirectional_iterator`^C++20	Specifies an iterator that can read and write both forwards and backwards.
`contiguous_iterator`^C++20	Specifies an iterator whose elements are sequential in memory, the same size, and can be accessed using pointer arithmetic.
`forward_iterator`^C++20	Specifies an iterator that can read (and possibly write) multiple times.
`input_iterator`^C++20	Specifies an iterator that you can read from at least once.
`input_or_output_iterator`^C++20	The basis of the iterator concept taxonomy.
`output_iterator`	Specifies an iterator that you can write to.
`random_access_iterator`^C++20	Specifies an iterator that you can read and write by index.
`sentinel_for`^C++20	Specifies a sentinel for an iterator type.
`sized_sentinel_for`^C++20	Specifies that an iterator and its sentinel can be subtracted (using `-`) to find their difference in constant time.

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