一个关于c++双向链表的问题

一个关于c++双向链表的问题

#include <iostream>
#include <string>

using namespace std;

struct Station
{
    string stationName;
    int minutes;
    Station *prev;
    Station *next;
};
Station *head = nullptr;

Station *generate_metro_line(int line_number, int station_number)
{
    Station *newstation = new Station;
    Station *head = newstation;
    head->stationName = "line" + to_string(line_number) + " station " + to_string(1);
    head->minutes = rand() % 5 + 1;
    Station *prev_station = head;
    int i = 1;
    while (i < station_number)
    {
        Station *current_station = new Station;
        current_station->stationName = "line" + to_string(line_number) + " station " + to_string(i + 1);
        current_station->minutes = rand() % 5 + 1;
        prev_station->next = current_station;
        current_station->prev = prev_station;
        tail = current_station;
        prev_station = current_station;
        i++;
    }
    return prev_station;
}

void output(Station *station)
{
    if (station == nullptr)
    {
        cout << station->stationName << ": end  station" << endl;
    }
    else   //错误出现的位置
    {
        cout << station->stationName << ": " << station->minutes << " minute(s) to next" << endl;
    }
}

void output_line(Station *firststation)
{

    while (firststation != nullptr)
    {
        output(firststation);
        firststation = firststation->next;
    }
}

struct Train
{
    string trainName;
    int leftTime;
    bool direction;
    Station *nextStation;
};

void init(Train &train, string trainName, Station *stopstation)
{
    train.trainName = trainName;
    train.leftTime = 0;
    train.direction = true;
    train.nextStation = stopstation;
}

void output(Train &train)
{
    if (train.direction)
    {
        cout << train.trainName << ": stop at " << train.nextStation->stationName << " for " << train.leftTime << " minutes" << endl;
    }
    else
    {
        cout << train.trainName << " is going to " << train.nextStation->stationName << " in " << train.leftTime << " minutes" << endl;
    }
}

void output_all_trains(int simulation_time, Train t[], int train_number)
{
    cout << "simulation time: " << simulation_time << " min" << endl;
    for (int i = 0; i < train_number; i++)
    {
        if (t[i].leftTime <= simulation_time)
        {
            output(t[i]);
        }
    }
}

int main()
{
    Train t[3];
    Station *station[2];
    int simulation_time = 0;
    int n1, n2;
    cout << "input number of stations of line 1:";
    cin >> n1;
    station[1] = generate_metro_line(1, n1);

    cout << "input number of stations of line 2:";
    cin >> n2;
    station[2] = generate_metro_line(2, n2);

    init(t[1], "train1", station[1]);
    init(t[2], "train2", station[2]);

    char choice;
    do
    {
        cout << "e end" << endl
             << "l line output" << endl
             << "t train output" << endl
             << "1 simulate 1 minute" << endl;
        cin >> choice;
        switch (choice)
        {
        case 'e':
            break;
        case 'l':
            int line_number;
            cout << "which line?" << endl;
            cin >> line_number;
            output_line(station[line_number]);
            break;
        case 't':
            output_all_trains(simulation_time, t, 3);
            break;
        case '1':
            simulation_time++;
            break;
        default:
            cout << "wrong input" << endl;
            break;
        }
    } while (choice != 'e');
    return 0;
}

请教各位朋友，这段代码中总是出现下图的错误，自己没有搞明白是为什么会出现这样的错误（个人感觉是没正确设置链表的头节点），并且能否讲述下解决的思路！(main函数中请主要查看case'l' ,自动忽略别的case错误，谢谢！）

Station *head = nullptr;
Station *generate_metro_line(int line_number, int station_number)
{
    Station *newstation = new Station;
    Station *head = newstation;
    head->stationName = "line" + to_string(line_number) + " station " + to_string(1);
    head->minutes = rand() % 5 + 1;
    Station *prev_station = head;
    int i = 1;
    while (i < station_number)
    {
        Station *current_station = new Station;
        current_station->stationName = "line" + to_string(line_number) + " station " + to_string(i + 1);
        current_station->minutes = rand() % 5 + 1;
  // 这里应该加一句
        current_station->next = prev_station->next; // 不然没有连起来
        prev_station->next = current_station;
        current_station->prev = prev_station;
        tail = current_station;
        prev_station = current_station;
        i++;
    }
    return prev_station;
}

另外 ouput 里 == nullptr 的分支应该返回 不应该访问空指针了