求解C++的出现的报错问题

Question

在multimap<int, Person> & personGroup(vector& v)返回值是引用会报错（下面是报错时在xtree文件的代码）：

 if (!_Rootnode->_Isnil) { // copy or move a node, then any subtrees
            bool_constant<is_same_v<key_type, value_type>> _Is_set;
            _Nodeptr _Pnode = _Copy_or_move(_Rootnode->_Myval, _Movefl, _Is_set);
            _Pnode->_Parent = _Wherenode;
            _Pnode->_Color  = _Rootnode->_Color;
            if (_Newroot->_Isnil) {
                _Newroot = _Pnode; // memorize new root
            }

而multimap<int, Person> personGroup(vector& v)这种不返回引用就能正常运行这是为什么。

#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<math.h>
#include"person.h"
using namespace std;

void printPerson(multimap<int, Person>& mp)
{
    cout << mp.begin()->first << endl;
    for (multimap<int, Person>::iterator it = mp.begin(); it != mp.end(); it++)
    {
        if (it->first == 1)
        {
            cout << "员工" << it->second.m_Name
                << "的工资为 " << it->second.m_Salary << " 元，"
                << "在策划部" << endl;
        }
        else if (it->first == 2)
        {
            cout << "员工" << it->second.m_Name
                << "的工资为 " << it->second.m_Salary << " 元，"
                << "在美术部" << endl;
        }
        else if (it->first == 3)
        {
            cout << "员工" << it->second.m_Name
                << "的工资为 " << it->second.m_Salary << " 元，"
                << "在研发部" << endl;
        }
    }
}

multimap<int, Person> & personGroup(vector<Person>& v)
{
    multimap<int, Person> mp;
    if (!v.empty())
    {
        for (vector<Person>::iterator it = v.begin(); it != v.end(); it++)
        {
            if ((*it).m_DId == 1)
            {
                mp.insert(pair<int, Person>((*it).m_DId, (*it)));
                //mp.insert(make_pair(1, *it));
            }
            else if ((*it).m_DId == 2)
            {
                mp.insert(pair<int, Person>((*it).m_DId, (*it)));
                /*mp.insert(make_pair(2, *it));*/
            }
            else if ((*it).m_DId == 3)
            {
                mp.insert(pair<int, Person>((*it).m_DId, (*it)));
                //mp.insert(make_pair(3, *it));
            }
        }
    }
    cout << "vector";
    return mp;
}


int main()
{
    vector<Person> v;
    v.push_back(Person("张三", 22, 1));
    v.push_back(Person("李四", 29, 3));
    v.push_back(Person("王五", 20, 3));
    v.push_back(Person("钱大", 36, 2));
    v.push_back(Person("赵二", 24, 1));
    v.push_back(Person("陈六", 25, 2));
    v.push_back(Person("孙七", 22, 2));
    v.push_back(Person("郑八", 21, 1));
    v.push_back(Person("魏九", 22, 1));
    v.push_back(Person("黄十", 26, 3));

    cout << v.size() << endl;

    cout << "nihhhhhhhhhhhhhhhh" << endl;

    multimap<int, Person> mp = personGroup(v);

    printPerson(mp);
    //pringPerson(personGroup(v));

    return 0;
}

Answer 1

函数personGroup中的mp是一个局部变量，函数返回后mp的内存就释放了，你不能返回一个局部变量的引用。