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Traits class defining properties of iterators.
Standard algorithms determine certain properties of the iterators passed to them and the range they represent by using the members of the corresponding iterator_traits instantiation.
For every iterator type, a corresponding specialization of iterator_traits class template shall be defined, with at least the following member types defined:
Note: For output iterators that are not at least forward iterators, any of these member types (except for iterator_category) may be defined as
The iterator_traits class template comes with a default definition that obtains these types from the iterator type itself (see below). It is also specialized for pointers (T*) and pointers to const (const T*).
Note that any custom class will have a valid instantiation of iterator_traits if it publicly inherits the base class std::iterator.
Output:
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
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<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
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<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
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<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
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<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
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<unordered_map>C++11
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<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
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<atomic>C++11
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<condition_variable>C++11
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<future>C++11
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<mutex>C++11
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<thread>C++11
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Other:
- <algorithm>
- <bitset>
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<chrono>C++11
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<codecvt>C++11
- <complex>
- <exception>
- <functional>
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<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
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<random>C++11
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<ratio>C++11
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<regex>C++11
- <stdexcept>
- <string>
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<system_error>C++11
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<tuple>C++11
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<type_traits>C++11
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<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
<iterator>
- iterator
- iterator_traits
functions
- advance
- back_inserter
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beginC++11
- distance
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endC++11
- front_inserter
- inserter
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make_move_iteratorC++11
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nextC++11
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prevC++11
iterator categories
predefined iterators
- Reference
- <iterator>
- iterator_traits
class template
<iterator>
std::iterator_traits
template <class Iterator> class iterator_traits;template <class T> class iterator_traits<T*>;template <class T> class iterator_traits<const T*>;
Iterator traits
Standard algorithms determine certain properties of the iterators passed to them and the range they represent by using the members of the corresponding iterator_traits instantiation.
For every iterator type, a corresponding specialization of iterator_traits class template shall be defined, with at least the following member types defined:
| member | description |
|---|---|
| difference_type | Type to express the result of subtracting one iterator from another. |
| value_type | The type of the element the iterator can point to. |
| pointer | The type of a pointer to an element the iterator can point to. |
| reference | The type of a reference to an element the iterator can point to. |
| iterator_category | The iterator category. It can be one of these: |
Note: For output iterators that are not at least forward iterators, any of these member types (except for iterator_category) may be defined as
void.The iterator_traits class template comes with a default definition that obtains these types from the iterator type itself (see below). It is also specialized for pointers (T*) and pointers to const (const T*).
Note that any custom class will have a valid instantiation of iterator_traits if it publicly inherits the base class std::iterator.
Member types
| member | generic definition | T* specialization | const T* specialization |
|---|---|---|---|
| difference_type | Iterator::difference_type | ptrdiff_t | ptrdiff_t |
| value_type | Iterator::value_type | T | T |
| pointer | Iterator::pointer | T* | const T* |
| reference | Iterator::reference | T& | const T& |
| iterator_category | Iterator::iterator_category | random_access_iterator_tag | random_access_iterator_tag |
Example
|
|
Output:
int* is a random-access iterator |
See also
- iterator
- Iterator base class (class template)
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