扩展代码，

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

struct Record {
    string name;
    // ... other fields ...

    bool operator<(const Record& other) const { return name < other.name; }

    friend ostream& operator<<(ostream& os, const Record& record) {
        os << record.name;  // Assuming that "name" is the only field to be printed
        return os;
    }
};

auto rec_eq = [](const Record& r1, const Record& r2) { return r1.name < r2.name; };  // compare names

void f(const vector<Record>& v) {
    auto er = equal_range(v.begin(), v.end(), Record{"Reg"}, rec_eq);
    for (auto p = er.first; p != er.second; ++p) {
        cout << *p << ' ';  // assuming that "<<" is defined for Record
    }
}

int main() {
    vector<Record> records = {{"Alice"}, {"Bob"}, {"Charlie"}, {"Dave"}, {"Eve"}, {"Reg"}, {"Reg"}, {"Reg"}};

    // Assume that the vector "records" is sorted based on the "name" field
    f(records);

    return 0;
}

这里主要是对 equal_range 的理解，这里传入给 equal_range 的 vector 必须是有序的，不管是升序还是降序，这个升序还是降序可以在 rec_eq 中体现。