c++ - how to avoid objects from array going out of scope after file is closed?

Question

So basically what is going on is this. The code works perfectly fine to add the objects into the array. But when I close the accountFile, the entire array becomes NULL. How can I avoid this so that I can use the array for other things?

accounts = new Account*[numAccounts];

for (int i = 0; !accountFile.eof(); i++)
{
    if (accountFile >> tempAccountType)
    {
        if (tempAccountType == "Checking")
        {
            accountFile >> tempAccountNum >> tempBalance >> tempTransFee;
            CheckingAccount tempAccount(tempBalance, tempAccountNum, tempTransFee);
            accounts[i] = &tempAccount;
        }
        else
        {
            accountFile >> tempAccountNum >> tempBalance >> tempIntRate;
            SavingsAccount tempAccount(tempBalance, tempAccountNum, tempIntRate);
            accounts[i] = &tempAccount;
        }
    }
}

Answer 1

std::vector<std::unique_ptr<Account>> accounts;

while(accountFile >> tempAccountType)
{
    if(tempAccountType == "Checking")
    {
        accountFile >> tempAccountNum >> tempBalance >> tempTransFee;
        accounts.emplace_back(new CheckingAccount(tempBalance, tempAccountNum, tempTransFee));
    }
    else
    {
        accountFile >> tempAccountNum >> tempBalance >> tempIntRate;
        accounts.emplace_back(new SavingsAccount(tempBalance, tempAccountNum, tempIntRate));
    }
}

1) 检查 !eof() 还不够好。我重组了循环

2) 使用向量

3) 使用智能指针（在本例中为 unique_ptr）

4) 不要存储指向本地范围对象的指针。你必须分配

Answer 2

问题不在于您关闭文件时，问题在于您正在对本地对象进行引用，当本地对象超出 socope 时该对象被破坏

首先，我将帐户定义为智能指针的向量

std::vector< shared_ptr<Account> > 

然后每次读取文件时创建一个新文件

accounts.push_back( make_shared<SavingsAccount)(tempBalance, tempAccountNum, tempTransFee);

只要向量存在，它就会存在。

Answer 3

由于您的对象的范围，会发生此错误。您的 tempAccount 对象在超出其范围时将被销毁。尝试这个：

//some stuff
if (tempAccountType == "Checking")
{
    accountFile >> tempAccountNum >> tempBalance >> tempTransFee;
    CheckingAccount *tempAccount=new CheckingAccount(tempBalance, tempAccountNum, tempTransFee);
    accounts[i]=tempAccount;
}
else
{
    accountFile >> tempAccountNum >> tempBalance >> tempIntRate;
    SavingsAccount *tempAccount=new SavingsAccount(tempBalance, tempAccountNum, tempIntRate);
    accounts[i] = tempAccount;
}

Answer 4

对象超出范围是因为它们是在 if 块中声明的。您通过引用保存它们，因此当它们超出范围时，引用变得无效。

尝试以下操作：

accounts[i] = tempAccount;

这将调用 for 的复制构造函数CheckingAccount，它将保存副本而不是引用。