Std::bad_alloc 在 While 循环中间抛出

Question

我正在编写一个处理订单输入文件 (csv) 的函数，使用 while 循环遍历它。

762212,1,2020-03-15,10951-3,64612-2,57544-1,80145-1,27515-2,16736-1,79758-2,29286-2,51822-3,39096-1,32641-3,63725-3,64007-2,23022-1,16974-3,26860-2,75536-2,26461-1
1,373975319551257,12-2023
258572,2,2020-03-15,96497-1,70616-1,80237-2,22248-2,56107-1,59695-1,37948-3,21316-3,63498-1,18329-1,56833-1,66295-1,47680-3,30346-1
1,201741963232463,02-2022
857003,3,2020-03-15,16655-1,88019-3,75069-3,96017-2,46883-2,15138-1,77316-1,70063-3,54452-3,86429-2,15134-2,60176-1,12946-3
2,cfeeham3s
747893,4,2020-03-17,48520-1,93268-2,63636-1,23750-2,99771-3,83203-1,21316-3,89921-2,15134-3,82831-1,30346-2,54044-3,28561-1,14792-2,23523-3,56826-2
1,3571379825697064,04-2025

每两行代表一个输入。我有以下处理此输入的函数：

list<Order> orders;

void read_orders(string file_name) {
    fstream read_file;
    read_file.open(file_name, ios::in);
    if (read_file.is_open()) {
        string s;
        int line_num = 1; // keeps track of line number in input file
        int o_id;
        string o_date;
        int c_id;
        vector<LineItem> itms;
        while (getline(read_file, s)) {
            cout << orders.size();        // shows that only two objects are added before failure
            if (line_num % 2 == 1) {      // handle odd numbered lines of input
                auto data = split(s, ',');
                int o_id = stoi(data[0]);
                string o_date = data[1];
                int c_id = stoi(data[2]);
                vector<LineItem> itms;
                // get line items
                int n_line_items = data.size() - 3;
                vector<string> end_data(data.end() - n_line_items, data.end());
                for (string x: end_data) {
                    auto parts = split(x, '-');
                    LineItem* it = new LineItem(stoi(parts[0]), stoi(parts[1]));
                    itms.push_back(*it);
                    delete it;
                }
            } else {                       // handle even numbered lines of input
                auto data = split(s, ',');
                Credit* pay_credit = new Credit(0.0, data[1], data[2]);  // initialize each type of payment
                PayPal* pay_paypal = new PayPal(0.0, data[1]);
                WireTransfer* pay_wire = new WireTransfer(0.0, data[1], data[2]);
                if (data[0] == "1") {
                    Order* ordr = new Order(o_id, o_date, c_id, itms, *pay_credit);
                    orders.push_back(*ordr);
                    delete ordr;
                } else if (data[0] == "2") {
                    Order* orr = new Order(o_id, o_date, c_id, itms, *pay_paypal);
                    orders.push_back(*orr);
                    delete orr;
                } else if (data[0] == "3") {
                    Order* odr = new Order(o_id, o_date, c_id, itms, *pay_wire);
                    orders.push_back(*odr);
                    delete odr;
                }
                delete pay_credit;  // trying to clean up memory
                delete pay_paypal;
                delete pay_wire;
            }

            line_num += 1;
        }
        read_file.close();
    }
}

由于我的 cout 语句，我可以看出它只在运行到 std::bad_alloc 错误之前将两项添加到列表中。当它在初始化时从添加 Credit 对象切换到将 PayPal 对象添加到 Order(...) 时，似乎会发生这种情况。我对为什么会发生这种情况进行了大量研究，所以我尽可能多地尝试清理（我是 C++ 的新手），但同样的错误不断出现。错误是在我向列表中添加内容时发生的，还是在我创建这些新对象时发生的？/我该如何解决类似的问题？

以下是我的 class 定义，以备不时之需：

class Payment {
public:
    double amount;
    string print_detail() {
        return "hey";
    };
};

class Credit: public Payment {
private:
    string card_number;
    string expiration;
public:
    Credit(double amt, string cn, string exp) {
        this->amount = amt;
        this->card_number = cn;
        this->expiration = exp;
    }
    string print_detail() {
        return "Credit card " + this->card_number + ", exp. " + this->expiration;
    }
};

class PayPal: public Payment {
private:
    string paypal_id;
public:
    PayPal(double amt, string pp_id) {
        this->amount = amt;
        this->paypal_id = pp_id;
    }
    virtual string print_detail() {
        return "Paypal ID: " + this->paypal_id;
    }
};

class WireTransfer: public Payment {
private:
    string bank_id;
    string account_id;
public:
    WireTransfer(double amt, string b_id, string a_id) {
        this->amount = amt;
        this->bank_id = b_id;
        this->account_id = a_id;
    }
    string print_detail() {
        return "Wire transfer from Bank ID " + this->bank_id + ", Account# " + this->account_id;
    }
};

class LineItem {
private:
    int item_id;
    int qty;
public:
    LineItem(int i_id, int qt) {
        this->item_id = i_id;
        this->qty = qt;
    }
    double subtotal() {
        double subtot = 0.0;
        for (auto x: items) {
            if (x.item_id == this->item_id) {
                subtot += x.price * this->qty;
            }
        }
        return subtot;
    };
};

class Order {
private:
    int order_id;
    string order_date;
    int cust_id;
    vector<LineItem> line_items;
    Payment payment;
public:
    Order(int o_id, string o_date, int c_id, vector<LineItem> li, Payment pay) {
        this->order_id = o_id;
        this->order_date = o_date;
        this->cust_id = c_id;
        this->line_items = li;
        this->payment = pay;
    }
    string pay_type = "";

    double total() {
        double result = 0.0;
        for (auto li: line_items) {
            result += li.subtotal();
        }
        return result;
    }
    string print_order() {
        string text = "===========================\nOrder #";
        text += to_string(this->order_id) + ", Date: " + this->order_date + "\nAmount: $";
        text += to_string(this->total()) + ", Paid by ";
        text += payment.print_detail();
        return text;
    }
};

这是显示它确实插入了两项的错误消息：

001122terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc
Process returned 3 (0x3)

Answer 1

std::bad_alloc 通常在没有足够的内存分配时抛出。我不能说这是否会解决问题，但是您重复分配和释放对象既不必要又有害（导致内存碎片）。

而不是

LineItem* it = new LineItem(stoi(parts[0]), stoi(parts[1]));
itms.push_back(*it);
delete it;

你应该做的

itms.push_back(LineItem(stoi(parts[0]), stoi(parts[1]));

或

itms.emplace_back(stoi(parts[0]), stoi(parts[1]));

这同样适用于 read_orders 中出现的每个 new。你不需要它们中的任何一个。

您可以做的另一件有用的事情是为 std::vector 预分配内存。如果您不知道它将包含多少项，请进行有根据的猜测（100、1000、10000 等）。

itms.reserve(1000); //before you start to push_back() to it

此外，如果您想传输其全部内容而不是制作副本，请确保 std::move 您的载体。

Std::bad_alloc 在 While 循环中间抛出

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