【发布时间】：2014-11-23 20:37:56
【问题描述】：
我将指针向量用于继承目的，并且我的所有行为都应有尽有，但是，我在从向量中删除对象时遇到了问题。
我创建了一个包含所有源文件的 Github gist，以及一个易于编译和运行的 Makefile：
https://gist.github.com/anonymous/7c689940992f5986f51e
问题主要出在这里：
我有一个这样的 Bank 类（注意 Account Database 结构，它是 Account* 的封装向量）：
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);
};
我有一个这样的模板数据库类，它创建指针向量：
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);
};
在我的银行中，我添加了 Account 对象，它们的定义如下：
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 ()
{
}
};
我正在将 Account 对象（主要是从基本 Account 类派生的类的 Chequing/Savings Accounts ）添加到 Bank，如下所示：
/*
* 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));
}
这一切都正常工作，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，它的定义如下：
/*
* 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;
}
}
}
这是我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。在删除功能中，您可以看到删除功能正在找到它应该正确删除的帐户。问题是，虽然它应该删除 Account #1，但它没有，但确实删除了该帐户的名称（如 Account #1 [C] [C] $1500.000000 与 Account #1 [C] testchq $1500.000000 所见）。
我在这里遇到了什么问题？我也不确定我这样做的方法，所以任何改进建议都将不胜感激。
提前致谢！
【问题讨论】：
标签： c++ pointers inheritance vector erase