C ++從指針向量中擦除元素

Question

我使用指針向量進行繼承，並且我的每個行為都應該如此，但是，我在向量中刪除對象時遇到問題。

我創建了一個包含所有源文件的Github gist，以及一個用於輕松編譯和運行的Makefile：

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

基本上這里是問題：

我有一個Bank類（請注意Account Database結構，它是Account *的封裝向量）：

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);
};

我有一個模板數據庫類，它創建指針向量：

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);
    };

在我的銀行中，我正在添加帳戶對象，其定義如下：

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 ()
        {
        }
};

我將Account對象（主要是基本Account類派生類的Chequing / Savings Accounts）添加到Bank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));
}

這一切都正常，我能夠從數據庫中提取對象並操縱我喜歡的方式。 問題在於刪除，其定義如下：

/*
 * 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;
    }
}

我創建了一個小測試文件來測試所有功能：

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;
        }
    }
}

這是運行文件后得到的輸出：

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

如您所見，它正確添加派生的Account類，並保留其派生類型而不進行對象切片。 在刪除功能中，您可以看到刪除功能正在查找應該正確刪除的帳戶。 問題是，雖然它應該刪除帳戶＃1，但它沒有，但它確實刪除了帳戶的名稱（如Account #1 [C] [C] $1500.000000 vs Account #1 [C] testchq $1500.000000 ）。

我在這里遇到的問題是什么？ 我也不確定我這樣做的方法，因此我們將非常感謝任何改進建議。

提前致謝！

Answer 1

您正在從副本中刪除該帳戶：

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

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

您需要從實際數據庫中刪除，因此您希望使用以下內容：

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

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