如何处理和避免递归

Question

我正在使用自定义类来管理自动售货机。我不知道为什么它一直抛出堆栈溢出错误。我的程序有两个版本，第一个是通过预定义某些变量来查看类等是否工作的基本测试。第二个版本应该是这样的，每次运行程序时，有问题的变量都会发生变化（取决于用户输入）。

如果有人能提出避免这种递归或堆栈溢出的方法，我会很好。下面是涉及的三个类的代码；

class Filling
{
protected:
    vector<Filling*> selection;
    string fillingChosen;

public:
    virtual float cost()
    {
        return 0;
    }
    virtual ~Filling(void)
    {
        //needs to be virtual in order to ensure Condiment destructor is called via Beverage pointer
    }
};

class CondimentDecorator : public Filling
{
public:
    Filling* filling;
    void addToPancake(Filling* customerFilling)
    {
        filling = customerFilling;
    }

    ~CondimentDecorator(void)
    {
        delete filling;
    }

};


class Frosted : public CondimentDecorator
{
    float cost()
    {       //ERROR IS HERE//
        return (.3 + filling->cost());
    }
};

下面是调用上述'cost'函数的代码；

void displayCost(Filling* selectedFilling)
{
    cout << selectedFilling->cost() << endl;
}

下面是启动它的部分代码（main方法）；

Filling* currentPancake = NULL;
            bool invalid = true;
            do
            {
                int selection = makeSelectionScreen(money, currentStock, thisState);
                invalid = false;

                if (selection == 1)
                {
                    currentPancake = new ChocolateFilling;
                }
                else if...

.
.
.
.
                else
                    invalid = true;


            } while (invalid);

            bool makingSelection = true;
            CondimentDecorator* currentCondiment = NULL;
                do
                {
                    int coatingSelection = makeCoatingSelectionScreen(money, currentStock, thisState);

                    if (coatingSelection == 1)
                        currentCondiment = new Frosted;
                    else if (coatingSelection == 2)...
.
.
.
                    else if (coatingSelection == 0)
                        makingSelection = false;

                    currentCondiment = thisSelection;
                    currentCondiment->addToPancake(currentPancake);
                    currentPancake = currentCondiment;
                    displayCost(currentPancake);



//Below is the code that DOES work, however it is merely meant to be a test. The 
//above code is what is needed to work, however keeps causing stack overflows
//and I'm uncertain as to why one version works fine and the other doesn't

                    /*currentCondiment = new Frosted;
                    currentCondiment->addToPancake(currentPancake);
                    currentPancake = currentCondiment;
                    displayCost(currentPancake);

                    currentCondiment = new Wildlicious;
                    currentCondiment->addToPancake(currentPancake);
                    currentPancake = currentCondiment;
                    displayCost(currentPancake);*/


                } while (makingSelection);

                displayCost(currentPancake);


                delete currentPancake;

Answer 1

当您使用Frosted 调用displayCost 时发生无限递归，而filling 也是Frosted。这就是发生在这里：

currentCondiment->addToPancake(currentPancake);
currentPancake = currentCondiment;
displayCost(currentPancake);

您将currentCondiment 的filling 设置为currentPancake，然后使用currentCondiment 调用displayCost。

---

在此过程中，您还泄漏了最初分配给currentPancake 的内存。

顺便说一句，currentCondiment = thisSelection; 也会泄漏内存。

想法：使用像std::unique_ptr 这样的智能指针来消除泄漏。