key_compare multimap_name.key_comp();

// C++ program to illustrate the
// multimap::key_comp() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
    // 创建名为m的multimap;
    multimap<char, int> m;
    multimap<char, int>::key_compare
        comp
        = m.key_comp();
    // 将元素插入到multimap中
    m.insert(make_pair('a', 10));
    m.insert(make_pair('b', 20));
    m.insert(make_pair('c', 30));
    m.insert(make_pair('d', 40));
    cout << "Multimap has the elements\n";
    //存储最后一个元素的键值
    char l = m.rbegin()->first;
    //初始化迭代器
    map<char, int>::iterator it = m.begin();
    //打印所有multimap的元素
    do {
        cout << it->first
             << " => "
             << it->second
             << '\n';
    } while (comp((*it++).first, l));
    return 0;
}

Multimap has the elements
a => 10
b => 20
c => 30
d => 40

// C++ program to illustrate the
// multimap::key_comp() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
    // 创建名为m的multimap;
    multimap<char, int> m;
    multimap<char, int>::key_compare
        comp
        = m.key_comp();
    // 将元素插入到multimap中
    m.insert(make_pair('a', 100));
    m.insert(make_pair('b', 200));
    m.insert(make_pair('c', 300));
    m.insert(make_pair('d', 400));
    cout << "Multimap has the elements\n";
    //存储最后一个元素的键值
    char l = m.rbegin()->first;
    //初始化迭代器
    map<char, int>::iterator it = m.begin();
    //打印所有multimap的元素
    do {
        cout << it->first
             << " => "
             << it->second
             << '\n';
    } while (comp((*it++).first, l));
    return 0;
}

Multimap has the elements
a => 100
b => 200
c => 300
d => 400