c++ - 交联 vector 中的段错误

Question

我正在尝试创建一个学生 vector 和一个大学 vector ，其中每个学生都有一份他正在申请的大学列表，每所大学都有一份已申请的学生列表。 但是当我运行代码时，出现“Segmentation fault: 11”。你能帮我理解我哪里做错了吗？

struct Student;

struct Univercity
{
    std::string name;
    int vacancies;
    std::vector<Student *> students;

    Univercity(std::string name,
               int vacancies)
        : name(name),
          vacancies(vacancies) {}
};

struct Student {
    std::string name, surname;
    int d, m, y;
    int points;
    std::vector<Univercity *> univercities;

    Student(std::string name,
            std::string surname,
            int d, int m, int y, int points,
            std::vector<Univercity *> univercities)
        : name(name),
          surname(surname),
          d(d), m(m), y(y),
          univercities(univercities) {}
};

void input(std::vector <Student> *students,
           std::vector <Univercity> *univercities) {
    int n;
    std::cin >> n;
    for (int i = 0; i < n; i++) {
        std::string name;
        int vacancies;
        std::cin >> name >> vacancies;
        univercities->push_back(Univercity(name, vacancies));
    }
    std::cin >> n;
    for (int i = 0; i < n; i++) {
        std::string name, surname;
        int d, m, y, points;
        int k;
        std::vector<Univercity *> applications;
        std::string uni_name;
        std::cin >> name >> surname >> d >> m >> y >> points >> k;
        for (int j = 0; j < k; j++) {
            std::cin >> uni_name;
            for (auto u : *univercities) {
                if (u.name == uni_name) {
                    applications.push_back(&u);
                    break;
                }
            }
        }
        students->push_back(Student(name, surname, d, m, y,
                                    points, applications));
    }

}

int main() {
    std::vector <Univercity> univercities;
    std::vector <Student> students;
    input(&students, &univercities);
    for (auto s : students) {
        std::cout << s.surname << " " << s.univercities.size() << "\n";
        for (auto u : s.univercities) {
            std::cout << u->name << " " << u->vacancies << "\n";
        }
    }
}

示例输入:

3
MSU 1
HSE 2
MIPT 100
5
Ivan Ivanov 1 1 1900 100 2 MSU HSE
Petr Petrov 2 1 1900 90 2 MSU HSE
Alexander Sidorov 3 1 1900 110 2 MIPT HSE
Ivan Petrov 3 1 1900 100 3 HSE MSU MIPT
Petr Ivanov 4 1 1900 80 1 HSE

Answer 1

当你阅读你的输入时:

for (auto u : *univercities) {
    if (u.name == uni_name) {
        applications.push_back(&u);
        break;
    }
}

在基于范围的 for 循环中，u 是 vector 中元素的拷贝。因此，一旦您离开循环，您插入 vector 的地址就无效了。使用

for (auto& u : *univercities) { //...

使用引用并避免复制。