std::reverse_iterator<Iter>::operator[]

 

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std::reverse_iterator

成员函数

reverse_iterator::reverse_iterator

reverse_iterator::operator=

reverse_iterator::base

reverse_iterator::operator*reverse_iterator::operator->

reverse_iterator::operator[]

reverse_iterator::operator++reverse_iterator::operator+reverse_iterator::operator+=reverse_iterator::operator--reverse_iterator::operator-reverse_iterator::operator-=

非成员函数

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

operator+

operator-

iter_move (C++20)

iter_swap (C++20)

make_reverse_iterator (C++14)

 

/* unspecified */ operator[]( difference_type n ) const;		(constexpr since C++17)

返回到指定相对位置的元素的引用。

参数

n

-

相对于当前位置的位置

返回值

current[-n - 1]

注释

返回类型被 LWG issue 386 更改为 unspecified，因为底层迭代器的 operator[] 的返回类型在当时也是 unspecified。

然而，从 N3066 开始，LegacyRandomAccessIterator 的 operator[] 的返回类型必须可转换为 reference。在所有常见的实现中，返回类型都被声明为 reference。另请参阅 LWG issue 2595。

示例

运行此代码

#include <array>
#include <cstddef>
#include <iostream>
#include <iterator>
#include <list>
#include <vector>
 
int main()
{
    int a[]{0, 1, 2, 3};
    std::reverse_iterator<int*> iter1{std::rbegin(a)};
    for (std::size_t i{}; i != std::size(a); ++i)
        std::cout << iter1[i] << ' '; // decltype(iter1[i]) is int&
    std::cout << '\n';
 
    std::vector v{0, 1, 2, 3};
    std::reverse_iterator<std::vector<int>::iterator> iter2{std::rbegin(v)};
    for (std::size_t i{}; i != std::size(v); ++i)
        std::cout << iter2[i] << ' '; // decltype(iter2[i]) is int&
    std::cout << '\n';
 
    // constexpr context
    constexpr static std::array<int, 4> z{0, 1, 2, 3};
    constexpr std::reverse_iterator<decltype(z)::const_iterator> iter3{std::crbegin(z)};
    static_assert(iter3[1] == 2);
 
    std::list li{0, 1, 2, 3};
    std::reverse_iterator<std::list<int>::iterator> iter4{std::rbegin(li)};
    *iter4 = 42;   // OK
//  iter4[0] = 13; // Compilation error: the underlying iterator
                   // does not model the random access iterator
}

输出

3 2 1 0
3 2 1 0

缺陷报告

以下行为更改缺陷报告被追溯应用于先前发布的 C++ 标准。

DR	应用于	已发布行为	正确行为
LWG 386	C++98	返回类型为 reference	设为 unspecified

参见

operator*operator->

访问指向的元素 (public member function)