Question

删除（T＆amp; item）应该删除headPtr并存储＆＃34;项值＆＃34; in＆＃34; item＆＃34;并返回true，否则如果队列中没有元素则返回false。我收到了＃34;读取访问冲突错误＆＃34;在这个功能。这是类和函数定义：

class SharedQueue {
public:
    SharedQueue();
    ~SharedQueue();

    //Return true if the queue is empty
    bool IsEmpty() const;

    //Enqueue the next item at the tail of the queue.
    void Add(T value);

    //Dequeue the next queue element and store it in "item" variable.  The function returns false if the queue is empty and no item can be retrieved.
    bool Remove(T &item);
    void Print();
private:
    struct QueueItem {
        T item;
        QueueItem *next;
    };
    //Fill in the The private data members.
    QueueItem *headPtr;
    QueueItem *tailPtr;
};

template <typename T> SharedQueue<T>::SharedQueue() {
    headPtr = NULL;
    tailPtr = NULL;
}

template <typename T>SharedQueue<T>::~SharedQueue() {
    QueueItem *temp;
    while (headPtr != NULL) {
        temp = headPtr;
        headPtr = headPtr->next;
        delete temp;
    }
}

template <typename T> bool SharedQueue<T>::IsEmpty() const {
    if (headPtr == NULL && tailPtr == NULL) {
        return true;
    }
    return false;
}

template <typename T> void SharedQueue<T>::Add(T aValue) {
    if (headPtr == NULL) {
        QueueItem *newItem = new QueueItem;
        newItem->item = aValue;
        tailPtr = headPtr = newItem;
    }
    else {
        QueueItem *newItem = new QueueItem;
        newItem->item = aValue;
        tailPtr->next = newItem;
        tailPtr = tailPtr->next;
    }
}

template <typename T> bool SharedQueue<T>::Remove(T &item) {
    if (headPtr == NULL) {
        return false;
    }
    else {
        QueueItem temp = *headPtr;
        item = headPtr->item;
        delete headPtr;
        headPtr = temp.next;
        return true;
    }
}

template <typename T> void SharedQueue<T>::Print() {
    QueueItem *temp = headPtr;
    while (temp != NULL) {
        std::cout << temp->item << "\n";
        temp = temp->next;
    }
}

Answer 1

将项目添加到非空QueueItem *newItem = new QueueItem; newItem->item = aValue; tailPtr->next = newItem; tailPtr = tailPtr->next;时：

newItem->next = NULL

您从未设置struct QueueItem。

您的私有Quote *myQuote; NSArray *myQuotes = theSubject.quotes; //START LOOP HERE for (myQuote in myQuotes){ NSLog(@" excerpt = %@", myQuote.excerpt); NSLog(@" desc2 = %@", myQuote.desc2); NSLog(@" quote_date = %@", myQuote.quote_date); NSLog(@" myQuote = %@", myQuote);可以（也许应该）拥有自己的构造函数/析构函数，以帮助确保这样的事情设置一致。

读取访问冲突（this-＆gt; headPtr为0xCDCDCDCD）

1 个答案: