为什么使用STL复制算法会出现"passing 'const Person' as 'this' argument discards qualifiers"？

Question

我正在尝试在用户定义的结构上实现最大堆，并且我使用 std::copy_n() 算法从 heap.in 文件中获取输入，但我从编译器收到此类错误:

passing 'const Person' as 'this' argument discards qualifiers

谁能告诉我问题出在哪里？

#include <fstream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <functional>
#include <iterator>
#include <string>
#include <iostream>


std::ifstream fin ("heap.in");
std::ofstream fout ("heap.out");

struct Person {
    int age;
    std::string name;

    bool operator < (const Person p) const{
        if (this->age != p.age)
            return this->age < p.age;
        return this->name < p.name;
    }

    friend std::istream& operator >> (std::istream& flux, Person& p) {
        flux >> p.name >> p.age;
        return flux;
    }

    friend std::ostream& operator << (std::ostream& flux, Person p) {
        flux << "(" << p.name << ", " << p.age << "); ";
        return flux;
    }

    friend std::ifstream& operator >> (std::ifstream& flux, Person& p) {
        flux >> p.name >> p.age;
        return flux;
    }

    friend std::ofstream& operator << (std::ofstream& flux, Person p) {
        flux << "(" << p.name << ", " << p.age << "); ";
        return flux;
    }
};

int n;
std::vector <Person> Heap;

int main () {
    fin >> n; 
    std::copy_n (Heap.begin (), n, std::istream_iterator <Person> (fin));
    return 0;
}

Answer 1

我猜你是这个意思

int main () {
    fin >> n;
    std::copy_n (std::istream_iterator <Person> (fin), n, std::back_inserter(Heap));
    return 0;
}

std::copy_n 将 n 项从第一个参数复制到第三个参数。如果要附加到矢量，则必须使用包装器 std::back_inserter，因为 std::copy_n 不会自行增加矢量的大小。

为什么使用STL复制算法会出现"passing 'const Person' as 'this' argument discards qualifiers"？

Why does appear "passing 'const Person' as 'this' argument discards qualifiers" while using STL copy algorithm?

c++

stl

copy

istream-iterator