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std::map<Key,T,Compare,Allocator>::end, std::map<Key,T,Compare,Allocator>::cend

来自 cppreference.com
< cpp‎ | container‎ | map
 
 
 
 
iterator end();
(1) (自 C++11 起无异常)
const_iterator end() const;
(2) (自 C++11 起无异常)
const_iterator cend() const noexcept;
(3) (自 C++11 起)

返回指向 map 的最后一个元素后的元素的迭代器。

此元素充当占位符;尝试访问它会导致未定义的行为。

range-begin-end.svg

内容

[编辑] 参数

(无)

[编辑] 返回值

指向最后一个元素后的元素的迭代器。

[编辑] 复杂度

恒定。

注释

libc++ 将 cend() 反向移植到 C++98 模式。

[编辑] 示例

#include <iostream>
#include <map>
 
int main()
{
    std::map<int, float> num_map;
    num_map[4] = 4.13;
    num_map[9] = 9.24;
    num_map[1] = 1.09;
    // Calls num_map.begin() and num_map.end()
    for (auto it = num_map.begin(); it != num_map.end(); ++it)
        std::cout << it->first << ", " << it->second << '\n';
}

输出

1, 1.09
4, 4.13
9, 9.24

[编辑] 使用自定义比较函数的示例

#include <cmath>
#include <iostream>
#include <map>
 
struct Point { double x, y; };
 
// Compare the x-coordinates of two Point pointers.
struct PointCmp
{
    bool operator()(const Point* lhs, const Point* rhs) const
    {
        return lhs->x < rhs->x; 
    }
};
 
int main()
{
    // Note that although the x-coordinates are out of order, the
    // map will be iterated through by increasing x-coordinates.
    Point points[3] = {{2, 0}, {1, 0}, {3, 0}};
 
    // mag is a map sending the address of node to its magnitude in the x-y plane.
    // Although the keys are pointers-to-Point, we want to order the map by the
    // x-coordinates of the points and NOT by the addresses of the Points. This
    // is done by using the PointCmp class's comparison method.
    std::map<Point*, double, PointCmp> mag(
        {{points, 2}, {points + 1, 1}, {points + 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.
        // If auto &i : mag was used instead, it will print the updated magnitude.
    }
}

输出

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

[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]