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

 

C++

编译器支持

独立和宿主

语言

标准库

标准库头文件

具名要求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

诊断库

内存管理库

元编程库 (C++11)

通用工具库

容器库

迭代器库

范围库 (C++20)

算法库

字符串库

文本处理库

数值库

日期和时间库

输入/输出库

文件系统库 (C++17)

并发支持库 (C++11)

执行控制库 (C++26)

技术规范

符号索引

外部库

 

容器库

序列

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

deque

forward_list (C++11)

list

关联

set

multiset

map

multimap

无序关联

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

适配器

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

视图

span (C++20)

mdspan (C++23)

表格

迭代器失效

成员函数表

非成员函数表

 

std::map

成员函数

map::map map::~map               map::operator= map::get_allocator

元素访问 map::at map::operator[] 迭代器 map::beginmap::cbegin (C++11) map::endmap::cend (C++11) map::rbeginmap::crbegin (C++11)      map::rendmap::crend (C++11) 容量 map::size map::max_size map::empty 观察器 map::key_comp map::value_comp 修改器 map::clear map::insert map::erase map::swap map::extract (C++17) map::merge (C++17) map::insert_range (C++23) map::insert_or_assign (C++17) map::emplace (C++11) map::emplace_hint (C++11) map::try_emplace (C++17) 查找 map::count map::find map::contains (C++20) map::equal_range map::lower_bound map::upper_bound

非成员函数

operator==operator<=> (C++20) std::swap(std::map) erase_if(std::map) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

推导指引 (C++17)

 

iterator end();	(1)	(noexcept since C++11)
const_iterator end() const;	(2)	(noexcept since C++11)
const_iterator cend() const noexcept;	(3)	(since C++11)

返回一个迭代器，指向 map 中最后一个元素之后的位置。

此元素充当占位符；尝试访问它会导致未定义的行为。

返回值

指向最后一个元素之后位置的迭代器。

复杂度

常数。

注解

libc++ 将 cend() 向后移植到 C++98 模式。

示例

运行此代码

#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

使用自定义比较函数的示例

运行此代码

#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

参见

begincbegin (C++11)	返回指向起始位置的迭代器 (public member function)
endcend (C++11)(C++14)	返回指向容器或数组末尾的迭代器 (function template)