std::iterator

 

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迭代器库

迭代器概念
readable (C++20) writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) 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
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (C++17 中弃用)	incrementable_traits (C++20) readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(C++20)
迭代器适配器
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) back_inserter front_inserter inserter
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) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

定义于头文件 <iterator>
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 是提供以简化迭代器所要求类型定义的基类。

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 <iostream>
#include <algorithm>
 
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)