std::iterator

 

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迭代器库

迭代器概念
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
迭代器原语
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (C++17 中弃用) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
算法概念与工具
间接可调用概念
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
常用算法要求
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
工具
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
迭代器适配器
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
流迭代器 istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	迭代器定制点 ranges::iter_move (C++20) ranges::iter_swap (C++20)
迭代器操作 advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	范围访问 begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

在标头 <iterator> 定义
template<     class Category,     class T,     class Distance = std::ptrdiff_t,     class Pointer = T*,     class Reference = T& > struct iterator;		(C++17 中弃用)

std::iterator 是为简化迭代器所要求的类型定义而提供的基类。

模板形参

Category	-	迭代器类别。必须是迭代器类别标签之一。
T	-	能通过解引用迭代器获得的值的类型。此类型对于输出迭代器应为 void。
Distance	-	能用于标识迭代器间距离的类型
Pointer	-	定义指向被迭代的类型（T）的指针
Reference	-	定义到被迭代的类型（T）的引用

成员类型

成员类型	定义
iterator_category	Category
value_type	T
difference_type	Distance
pointer	Pointer
reference	Reference

示例

以下示例演示如何通过继承 std::iterator 实现输入迭代器

运行此代码

#include <algorithm>
#include <iostream>
 
template<long FROM, long TO>
class Range
{
public:
    // 通过继承自 std::iterator 提供成员 typedef
    class iterator : public std::iterator<
                                std::input_iterator_tag, // iterator_category
                                long,                    // value_type
                                long,                    // difference_type
                                const long*,             // pointer
                                long                     // reference
                            > {
        long num = FROM;
    public:
        explicit iterator(long _num = 0) : num(_num) {}
        iterator& operator++() { num = TO >= FROM ? num + 1: num - 1; return *this; }
        iterator operator++(int) { iterator retval = *this; ++(*this); return retval; }
        bool operator==(iterator other) const { return num == other.num; }
        bool operator!=(iterator other) const { return !(*this == other); }
        reference operator*() const { return num; }
    };
    iterator begin() { return iterator(FROM); }
    iterator end() { return iterator(TO >= FROM? TO + 1 : TO - 1); }
};
 
int main()
{
    // std::find 要求输入迭代器
    auto range = Range<15, 25>();
    auto itr = std::find(range.begin(), range.end(), 18);
    std::cout << *itr << '\n'; // 18
 
    // Range::iterator 亦满足基于范围的 for 要求
    for (long l : Range<3, 5>())
        std::cout << l << ' '; // 3 4 5
    std::cout << '\n';
}

输出：

18
3 4 5

参阅

iterator_traits	为迭代器各项性质提供统一接口 (类模板)
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	用于指示迭代器类别的空类类型 (类)