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std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::end, std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::cend

来自 cppreference.com
< cpp‎ | 容器‎ | 无序映射
 
 
 
 
iterator end() noexcept;
(1) (自 C++11)
const_iterator end() const noexcept;
(2) (自 C++11)
const_iterator cend() const noexcept;
(3) (自 C++11)

返回指向unordered_map最后一个元素之后的元素的迭代器。

此元素充当占位符;尝试访问它会导致未定义行为。

range-begin-end.svg

内容

[编辑] 参数

(无)

[编辑] 返回值

指向最后一个元素之后的元素的迭代器。

[编辑] 复杂度

常数。

[编辑] 示例

#include <cmath>
#include <iostream>
#include <unordered_map>
 
struct Node { double x, y; };
 
int main()
{
    Node nodes[3] = {{1, 0}, {2, 0}, {3, 0}};
 
    // mag is a map mapping the address of a Node to its magnitude in the plane
    std::unordered_map<Node*, double> mag =
    {
        { nodes + 0, 1 },
        { nodes + 1, 2 },
        { nodes + 2, 3 }
    };
 
    // Change each y-coordinate from 0 to the magnitude
    for (auto iter = mag.begin(); iter != mag.end(); ++iter)
    {
        auto cur = iter->first; // pointer to Node
        cur->y = mag[cur]; // could also have used cur->y = iter->second;
    }
 
    // Update and print the magnitude of each node
    for (auto iter = mag.begin(); iter != mag.end(); ++iter)
    {
        auto cur = iter->first;
        mag[cur] = std::hypot(cur->x, cur->y);
        std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
        std::cout << iter->second << '\n';
    }
 
    // Repeat the above with the range-based for loop
    for (auto i : mag)
    {
        auto cur = i.first;
        cur->y = i.second;
        mag[cur] = std::hypot(cur->x, cur->y);
        std::cout << "The magnitude of (" << cur->x << ", " << cur->y << ") is ";
        std::cout << mag[cur] << '\n';
        // Note that in contrast to std::cout << iter->second << '\n'; above, 
        // std::cout << i.second << '\n'; will NOT print the updated magnitude
    }
}

可能的输出

The magnitude of (3, 3) is 4.24264
The magnitude of (1, 1) is 1.41421
The magnitude of (2, 2) is 2.82843
The magnitude of (3, 4.24264) is 5.19615
The magnitude of (1, 1.41421) is 1.73205
The magnitude of (2, 2.82843) is 3.4641

[编辑] 另请参阅

返回指向开头的迭代器
(公有成员函数) [编辑]
(C++11)(C++14)
返回指向容器或数组末尾的迭代器
(函数模板) [编辑]