C++出队问题......出队重复返回相同的元素

Question

所以我有下面的代码片段...

for(int k=0; k<10; k++){
    State newState;
    newState = queue.dequeue();
    //...do stuff with `newState`...
}

我遇到的问题是，经过几个小时的测试，我意识到每次代码到达 时，newState 都会使 State 的完全相同的实例出队newState = queue.dequeue()，而不是以 FIFO 方式弹出一个新元素......我似乎无法弄清楚我到底做错了什么:/

下面是我的队列类 .h 和 .cpp 代码...

//queue.h

#include <iostream>
#include <stdio.h>

#include "state.h"

using namespace std;

// Node class
class Node {
public:
    State elem;
    Node* next;
    Node() {}
    State Elem() { return elem; }
    Node* Next() { return next; }
};

// Queue class
class Queue {
    Node *head;
    Node *tail;
  public:
    Queue();
    ~Queue();
    bool isEmpty();
    int size();
    void enqueue(State);
    State dequeue();
};

还有我的 .cpp 文件...

//queue.cpp

#include "queue.h"

#include <iostream>

Queue::Queue(){
    head = NULL;
    tail = NULL;
}

Queue::~Queue(){
    if(!isEmpty()){
        while(head){
            Node *del = head;
            head = head->next;
            delete del;
        }
    }
}

bool Queue::isEmpty(){
    return head == NULL;
}

int Queue::size(){
    int count = 0;
    if(isEmpty()){
        return count;
    } else {
        Node *temp = head;
        while(temp){
            temp = temp->next;
            count++;
        }
        delete temp;
        return count;
    }
}

//insert s to back of queue
void Queue::enqueue(State s){
    Node* newNode = new Node();
    newNode->elem = s;
    newNode->next = NULL;
    if(s.checkZ()){
        cout << "Puzzle solved!" << endl << endl;
        exit(0);
    }
    if(head==NULL){
        head = tail = newNode;
    } else {
        tail->next = newNode;
        tail = newNode;
    }
}

//remove State from front of queue
State Queue::dequeue(){
    if(isEmpty()){
        cout << "This puzzle has no solution." << endl;
        cout << "Exiting program..." << endl << endl;
        exit(0);
    } else {
        State ret = head->Elem();
        Node *del = head;
        head = head->next;
        delete del;
        return ret;
    }
}

在此先感谢您的帮助，我很乐意根据请求显示我的代码的任何其他片段

编辑:这是我的 State 复制构造函数...

State::State(const State &rhs){
    pieces = rhs.pieces;
    pieceCount = rhs.pieceCount;
    rows = rhs.rows; cols = rhs.cols;
    currentState = rhs.currentState;
    prevStates = rhs.prevStates;
    prevStateCount = rhs.prevStateCount;
    moves = rhs.moves;
    moveCount = rhs.moveCount;
}

Answer 1

在 size()

delete temp;

虽然不危险，但因为此时 temp 为空，所以它看起来很可疑。您还可以删除 if/else，因为当 head 为 null 时，count 不会递增。

否则我不明白为什么它会一次又一次地返回相同的元素。唯一的原因可能是一些代码，它多次插入相同的元素。