C++ 从指针 vector 中删除元素

Question

我正在使用一个指针 vector 来实现继承目的，并且我的每一个行为都应该如此，但是，我在从 vector 中删除对象时遇到了问题。

我已经创建了一个包含所有源文件的 Github gist，以及一个便于编译和运行的 Makefile:

https://gist.github.com/anonymous/7c689940992f5986f51e

本质上就是问题所在:

我有一个 Bank 类(注意账户数据库结构，它是账户 * 的封装 vector ):

class Bank
{
private:
    Database<Account> m_acctDb;
    Database<User> m_userDb;
    int m_accountCounter;
    int m_userCounter;
public:
    Bank ();
    ~Bank ();

    // Accessor Methods.
    int getAccountCounter () const;
    int getUserCounter () const;
    int getNumAccounts () const;
    int getNumUsers () const;
    Database<Account> getAccountDatabase () const;
    Database<User> getUserDatabase () const;
    User *getUser (int userId);
    Account *getAccount (int accountId);
    std::vector<ChequingAccount> getChequingAccounts () const;
    std::vector<SavingsAccount> getSavingsAccounts () const;
    std::vector<Manager> getManagers () const;
    std::vector<Customer> getCustomers () const;
    std::vector<Maintenance> getMaintenance () const;

    // Mutator Methods.
    void addChequing (int userId, double balance = 0, std::string name =
            "");
    void addSavings (int userId, double balance = 0,
            std::string name = "");
    void addCustomer (std::string firstName, std::string lastName,
            std::string password, std::string username);
    void addManager (std::string firstName, std::string lastName,
            std::string password, std::string username);
    void addMaintenance (std::string firstName, std::string lastName,
            std::string password, std::string username);
    void deleteAccount (int accountId);
    void deleteUser (int userId);
};

我有一个模板数据库类，它创建指针 vector :

template<class T>
    class Database
    {
        protected:
            std::vector<T*> m_database;
        public:
            Database ();
            virtual ~Database ();
            std::vector<T*> getDatabase () const;
            void add (T *Object);
            bool del (int id);
    };

在我的银行中，我添加了如下定义的 Account 对象:

class Account
{
    protected:
        int m_id, m_userId, m_type;
        double m_balance;
        std::string m_name;
        std::vector<std::string> m_history;
public:
    Account (int id, int userId, double balance = 0,
            std::string name = "");
    virtual ~Account ();

    // Accessor Methods.
    int getId () const;
    int getUserId () const;
    int getType () const;
    double getBalance () const;
    std::string getName () const;
    std::string getDetails () const;
    std::vector<std::string> getHistory () const;

    // Mutator Methods.
    void setName (std::string name);
    void depositFunds (double amount);
    virtual bool withdrawFunds (double amount);
};

/*
 * Chequing account type
 */
class ChequingAccount : public Account
{
    public:
        ChequingAccount (int id, int userId, double balance = 0,
                std::string name = "") :
                Account(id, userId, balance, name)
        {
            // Chequing account type.
            m_type = CHEQ;

            // If no name was given.
            if (name == "")
            {
                // Give account a generic name.
                m_name = "Chequing Account #" + std::to_string(id);
            }
            else
            {
                m_name = name;
            }
        }

        ~ChequingAccount ()
        {
        }

        virtual bool withdrawFunds (double amount);
};

/*
 * Savings account type
 */
class SavingsAccount : public Account
{
    public:
        SavingsAccount (int id, int userId, double balance, std::string name) :
                Account(id, userId, balance, name)
        {
            // Savings account type.
            m_type = SAVE;

            // If no name was given.
            if (name == "")
            {
                // Give account a generic name.
                m_name = "Savings Account #" + std::to_string(id);
            }
            else
            {
                m_name = name;
            }
        }

        ~SavingsAccount ()
        {
        }
};

我正在将帐户对象(主要是支票/储蓄帐户，它们是基帐户类的派生类)添加到银行中:

/*
 * Adds a new chequing account to the bank database.
 */
void Bank::addChequing (int userId, double balance, std::string name)
{
    m_acctDb.add(new ChequingAccount(++m_accountCounter, userId, balance, name));
}

/*
 * Adds a new savings account to the bank database.
 */
void Bank::addSavings (int userId, double balance, std::string name)
{
    m_acctDb.add(new SavingsAccount(++m_accountCounter, userId, balance, name));
}

这一切工作正常，我能够从数据库中提取对象并按照我喜欢的方式进行操作。问题在于删除，其定义如下:

/*
 * Deletes the specified account from the bank database.
 */
void Bank::deleteAccount (int accountId)
{
    std::vector<Account*> db = m_acctDb.getDatabase();
    std::vector<Account*>::iterator it = db.begin();
    cout << "Searching for account " << accountId << endl;
    while (it != db.end())
    {
        if ((*it)->getId() == accountId)
        {
            cout << "Found account 1" << endl;
            // Delete selected account.
            delete (*it);
            it = db.erase(db.begin());
        }
        else ++it;
    }
}

我创建了一个小测试文件来测试所有功能:

int main ()
{
    Bank bank;

    cout << "Num accounts in bank: " << bank.getNumAccounts() << endl << endl;

    cout << "Adding accounts to bank..." << endl;
    bank.addChequing(1, 1500.0, "testchq");
    bank.addSavings(1, 2000.0, "testsav");

    cout << "Num accounts in bank: " << bank.getNumAccounts() << endl;
    for (int i = 0; i < bank.getNumAccounts(); ++i)
    {
        if (bank.getAccount(i + 1) == NULL) cout << "Account is NULL" << endl;
        else
        {
            cout << bank.getAccount(i + 1)->getDetails() << endl;
        }
    }
    cout << endl;

    cout << "Deleting account 1..." << endl;
    bank.deleteAccount(1);
    cout << endl;

    cout << "Num accounts in bank: " << bank.getNumAccounts() << endl;
    for (int i = 0; i < bank.getNumAccounts(); ++i)
    {
        if (bank.getAccount(i + 1) == NULL) cout << "Account is NULL" << endl;
        else
        {
            cout << bank.getAccount(i + 1)->getDetails() << endl;
        }
    }
}

这是运行文件后得到的输出:

Num accounts in bank: 0

Adding accounts to bank...
Num accounts in bank: 2
Account #1 [C] testchq $1500.000000
Account #2 [S] testsav $2000.000000

Deleting account 1...
Searching for account 1
Found account 1

Num accounts in bank: 2
Account #1 [C] [C] $1500.000000
Account #2 [S] testsav $2000.000000

如您所见，它正确地添加了派生的 Account 类，并在没有对象切片的情况下保留了它们的派生类型。在删除函数中，可以看到删除函数正在正确找到应该删除的账户。问题是虽然它应该删除帐户 #1，但它没有删除，但它确实删除了帐户名称(如 Account #1 [C] [C] $1500.000000 与 Account 所示#1 [C] testchq $1500.000000).

我在这里遇到的问题是什么？我也不确定我这样做的方法，因此非常感谢任何改进建议。

提前致谢!

Answer 1

您要从拷贝中删除帐户:

std::vector<T*> getDatabase () const;

std::vector<Account*> db = m_acctDb.getDatabase();

您需要从实际数据库中删除，因此您希望用法为:

std::vector<T*>& getDatabase ();
const std::vector<T*>& getDatabase () const;

std::vector<Account*>& db = m_acctDb.getDatabase();