Question

作为序言，我是编程新手。我正在写一个简单的购物清单程序，我有一个do-while循环菜单驱动程序。选择1时，它会提示用户输入4个数据，然后发送给我的Item Class构造函数以启动值。然后我将Item添加到List Class数组，然后它会返回菜单。当从菜单中选择3时，它应该显示列表但由于某种原因我得到了分段错误。我现在已经连续工作了2天，但无法理解（我的TA也不能）。我将数据硬编码到我的函数中以查看它们是否正常工作，我在显示列表，添加项目或删除项目方面没有任何问题。当我尝试使用菜单中的功能时，唯一的问题就出现了。请帮忙！！！

主要功能：

int main()
{
/*List sl1;

Item Item1("apple", "unit", 3, 2.00);
Item Item2("grapes", "Pounds", 4, 5.00);
Item Item3("banana", "unit", 6, 2.00);
Item Item4("pears", "ounces", 5, 1.00);

sl1.addItem(&Item1);
sl1.addItem(&Item2);
sl1.addItem(&Item3);
sl1.addItem(&Item4);

sl1.removeItem("banana");
sl1.removeItem("grapes");
sl1.removeItem("pears");

cout << "Total Price: " << sl1.totalPrice() << endl;

sl1.displayList();
*/
int menuChoice;
List sl;
        do
        {
            cout << endl;
            cout << "1. Add Item to Shopping List" << endl;
            cout << "2. Remove Item from Shopping List" << endl;
            cout << "3. Display Shopping List" << endl;
            cout << "4. Quit" << endl << endl;

            cout << "Please Select 1-4: ";
            cin >> menuChoice;

            if (menuChoice == 1)
            {
                string name;
                string units;
                int quantity;
                double cost;

                cout << endl;
                cout << "Enter Item Name: " << endl;
                cin.ignore(256, '\n');
                getline(cin, name);

                cout << "Enter Item Units (eg. Ounces, Cans): " << endl;
                getline(cin, units);

                cout << "Enter Number of Units Needed: " << endl;
                cin >> quantity;

                cout << "Enter Cost of Item Per Unit: " << endl;
                cin >> cost;

                Item Item1(name, units, quantity, cost);

                sl.addItem(&Item1);

                //sl.displayList();

            }

            else if (menuChoice == 2)
            {
                string name;

                cout << "Please enter the name of the Item you wish to remove: " << endl;
                getline(cin, name);

                sl.removeItem(name);
            }

            else if (menuChoice == 3)
            {
                sl.displayList();

                cout << "Total Price: " << sl .totalPrice() << endl << endl;
            }
        } while (menuChoice != 4);

return 0;

}

列表类：

List::List()
{
arrayEnd = 0;
for (int count = 0; count < 4; count++)
{
    shoppingList[count] = NULL;
}
}

void List::addItem(Item* inputItem)
{
shoppingList[arrayEnd] = inputItem;
arrayEnd++;
}

void List::removeItem(string itemName)
{
int removedItem = 0;

for (int count = 0; count < arrayEnd; count++)
{
    if (itemName == shoppingList[count]->getItemName())
    {
        shoppingList[count] = NULL;

        removedItem = count;
    }
}

for (int count = 0; count < arrayEnd; count++)
{
    if (count > removedItem)
    {
        shoppingList[count - 1] = shoppingList[count];
        shoppingList[count] = NULL;

        arrayEnd = arrayEnd - 1;
    }
}
}

double List::totalPrice()
{
double totalPrice = 0.0;

if (shoppingList[0] == NULL)
{
    cout << "There are no items in the list" << endl;
}
else 
{
    for (int count = 0; count < arrayEnd; count++)
    {
        totalPrice += shoppingList[count]->getUnitPrice() * shoppingList[count]->getNumberToBuy();
    }
}

return totalPrice;
}

void List::displayList()
{
if (shoppingList[0] == NULL)
{
    cout << "There are no items in the list" << endl;
}
else
{
    for (int count = 0; count < arrayEnd; count++)
    {
        cout << "Item: " << shoppingList[count]->getItemName() << endl;
        cout << "Units: " << shoppingList[count]->getItemUnit() << endl;
        cout << "Quantity: " << shoppingList[count]->getNumberToBuy() << endl;
        cout << "Subtotal: " << shoppingList[count]->getUnitPrice()*shoppingList[count]->getNumberToBuy() << endl << endl;
    }
}
}

Answer 1

问题在于：

Item Item1(name, units, quantity, cost);
sl.addItem(&Item1);

Item1位于if块内，因此它将在块的出口处被破坏。因此，您添加了一个指向不再存在的对象的指针，以及bam，seg fault。从技术上讲，你已经离开了所谓的悬空指针。这是一个非常危险的野兽。

PS：如果我是你，我会改变我的TA，因为这是C ++用户应该注意的一些常见的C ++错误。

分段错误通过菜单运行时

1 个答案: