嘗試刪除對象時崩潰

Question

嘗試刪除我創建的對象時，我的程序崩潰了。 認為刪除使用關鍵字new創建的對象是安全的。

為什么會發生這種情況？

這是代碼：

標題

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

template<typename T>
class Postgre {
public:
    Postgre();

    std::vector<T*> get_user();
    std::vector<T*> get_fake_user();

    ~Postgre();
};

class User {
public:
    User(short id, std::string first_name, std::string last_name) {
        this->ID = id;
        this->first_name = first_name;
        this->last_name = last_name;
    }

    short ID;
    std::string first_name;
    std::string last_name;
};

class Fake_User {
public:
    Fake_User(short id, std::string user_name, std::string user_pw) {
        this->ID = id;
        this->user_name = user_name;
        this->user_pw = user_pw;
    }

    short ID;
    std::string user_name;
    std::string user_pw;
};

來源

template<typename T>
Postgre<T>::Postgre() {

}

template<typename T>
Postgre<T>::~Postgre() {
}

template<typename T>
std::vector<T*> Postgre<T>::get_user() {
    T* user = new T(1, "Peter", "Peters");
    std::vector<T*> result;

    result.push_back(user);
    delete user;
    return result;
}

template<typename T>
std::vector<T*> Postgre<T>::get_fake_user() {
    T* fake_user = new T(2, "Beverly", "Peters");
    std::vector<T*> result;

    result.push_back(fake_user);
    delete fake_user;
    return result;
}

template class Postgre<User>;
template class Postgre<Fake_User>;

主要的

int _tmain(int argc, _TCHAR* argv[]){
   Postgre<User>* postgre = new Postgre<User>();

   //test User Class:
   std::vector<std::vector<User*>> list_user;
   list_user.push_back(postgre->get_user());

    std::cout << list_user[0][0]->ID << std::endl;
    std::cout << list_user[0][0]->first_name << std::endl;
    std::cout << list_user[0][0]->last_name << std::endl;

    std::cout << std::endl;
    //test Fake_User Class:
    Postgre<Fake_User>* postgre2 = new Postgre<Fake_User>();

    std::vector<std::vector<Fake_User*>> list_fake_user;
    list_fake_user.push_back(postgre2->get_fake_user());

    std::cout << list_fake_user[0][0]->ID << std::endl;
    std::cout << list_fake_user[0][0]->user_name << std::endl;
    std::cout << list_fake_user[0][0]->user_pw << std::endl;

    //wait for keypress
    std::cin.ignore();

    return 0;
}

Answer 1

在

template<typename T>
std::vector<T*> Postgre<T>::get_user() {
    T* user = new T(1, "Peter", "Peters"); 
    std::vector<T*> result;

    result.push_back(user); // you copy the pointer into result
    delete user; // you delete the pointer, now user is dangling
    return result; // on exit, the pointer user in vector result is dangling
}

您返回一個存儲已刪除（懸空）指針的向量。 請注意， push_back復制指針（即內存位置），因此它存儲已標記為已刪除的內存位置。