带链接列表的C ++优先级队列类(C++ Priority Queue Class with Linked List)

 我的c ++代码存在两个问题（测试文件如下）： 
 
 我似乎无法弄清楚为什么它没有突破while循环，在运行时，它卡在循环“7对325”。 
 
 所以它应该进入temp的下一个节点，它将为null，然后跳转到它将它添加到队列末尾的部分。 但它只是循环和循环。 
 
 我的第二个问题是我已经注释掉的函数，queue1.back，无论什么时候运行，它只是出错并给出看起来像是地址，但.front（）函数工作得很好。 
 
 我正在使用的测试文件是这样的： 
 
 89 Alex 
 
 325 Rob 
 
 72 Joy 
 
 91 Bob 
 
using namespace std;

class Person
{
    friend class Pqueue;
    public:
        int priority;
        string name;
    };


    class PQueue
    {
        friend class Person;

        private:

        //Structure for my linked list.
        typedef struct node {
            Person data;
            struct node *next;
        }Node, *NodePtr;

        Node *head, *tail;

        public:
        //Prototype Functions
        PQueue(void);              //Initializer function
        bool empty(void);          //Test if empty
        int size(void);            //Return size
        void enqueue(Person *);    //Insert Node
        void dequeue(void);        //Remove Node
        Person* front(void);       //Access Next Node
        Person* back(void);        //Access last node

    };



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



    bool PQueue::empty(){
        return (head == NULL);
    }



    void PQueue::enqueue(Person *myPerson){
        NodePtr np = (NodePtr) malloc(sizeof(Node));
        np->data = *myPerson;
        np->next = NULL;

        if(empty())
        {
             cout << "Making into creating the first node, of the linked list" <<endl;
             head = np;
             tail = np;
         }
         else { //Queue has more the one node
               Node* temp = head;
               if(np->data.priority > temp->data.priority) //If the priority is greater then the rest.
               {
                   head = temp;                            //Saving my head pointer
                   head->data = np->data;                  //Assigning new Data to the head pointer
                   head->next = temp;                      //Assigning the rest of the linked list back into head.
                   cout << "Making into creating the first node again, having to reassign." <<endl;
               }
               else{
                    //Searching where to place the node.
                    while(temp->data.priority > np->data.priority) //Searching if the next priority is higher then the passed.
                    {
                        cout << "Inside the while loop: " << np->data.priority << " versus "<<temp->data.priority <<endl;
                        if(temp->next == NULL)
                            break;
                        temp = temp->next;
                     }

            if(temp->next == NULL && np->data.priority < temp->data.priority) //Inserting at the end.
            {
                cout << "Making into creating the last node" <<endl;
                tail->next = np;
                cout << "Passing the function of creating the last node" <<endl;
            }
            else   //Inserting into the middle of the function.
            {
                cout << "Inserting in the middle of the queue" <<endl;
                np->next = temp->next;
                temp->next = np;
            }
        }
    }
}



void PQueue::dequeue(){
    if(empty()){
        cout << "\nAttempt to remove from an empty list." << endl;
        exit(1);
    }

    Person hold = head->data;
    NodePtr temp = head;
    head=head->next;
    if (head == NULL) tail = NULL;
    free(temp);
}

Person* PQueue::front(){
    //Person &temp = head->next->data;
    //Person &temp = head->data;
    Person &temp = head->data;
    return &temp;
}

Person* PQueue::back(){
    if(empty()){
        cout << "\nNo entries in list." << endl;
        exit(1);
    }
    Person &temp = tail->data;
    return &temp;
}

int main() {
    cout << "Starting main" << endl;
    PQueue queue1; //Creating my queue.
    cout << "Created Queue" << endl;
    Person tempPerson;
    ifstream inFile;
    inFile.open("/tmp/temp");
    cout << "going into while loop" << endl;

    while (inFile >> tempPerson.priority >> tempPerson.name){
        cout << "The priority is " <<  tempPerson.priority << " the name is " << tempPerson.name <<endl;
        queue1.enqueue(&tempPerson);
    }


    //Testing Section, trying to get .front and .back to work.
    Person *testPerson;
    testPerson = queue1.front();
    cout << "The TEST priority is " <<  testPerson->priority << " the TEST name is " << testPerson->name <<endl;
    /**
    Person *tailPerson;
    testPerson = queue1.back();
    cout << "The TEST priority is " <<  tailPerson->priority << " the TEST  name is " << tailPerson->name <<endl;
    **/

    queue1.dequeue();
    queue1.dequeue();
    queue1.dequeue();


    return 0;
}

I am having two issues with my c++ code (The test file is below): 
 
I can't seem to figure out why its not breaking out of the while loop, when running, its stuck on the loop "7 versus 325".
 
So it should go into the next node of temp, which would be null, and then jump into the section where it adds it to the end of the queue. But its just looping and looping. 
 
My second issue is with the the function I have commented out, queue1.back, whenever that is ran, it just errors out and gives what appears to be the address, but the .front() function works just fine. 
 
The Test File I am working with is like this:
 
89 Alex
 
325 Rob
 
72 Joy
 
91 Bob
 
using namespace std;

class Person
{
    friend class Pqueue;
    public:
        int priority;
        string name;
    };


    class PQueue
    {
        friend class Person;

        private:

        //Structure for my linked list.
        typedef struct node {
            Person data;
            struct node *next;
        }Node, *NodePtr;

        Node *head, *tail;

        public:
        //Prototype Functions
        PQueue(void);              //Initializer function
        bool empty(void);          //Test if empty
        int size(void);            //Return size
        void enqueue(Person *);    //Insert Node
        void dequeue(void);        //Remove Node
        Person* front(void);       //Access Next Node
        Person* back(void);        //Access last node

    };



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



    bool PQueue::empty(){
        return (head == NULL);
    }



    void PQueue::enqueue(Person *myPerson){
        NodePtr np = (NodePtr) malloc(sizeof(Node));
        np->data = *myPerson;
        np->next = NULL;

        if(empty())
        {
             cout << "Making into creating the first node, of the linked list" <<endl;
             head = np;
             tail = np;
         }
         else { //Queue has more the one node
               Node* temp = head;
               if(np->data.priority > temp->data.priority) //If the priority is greater then the rest.
               {
                   head = temp;                            //Saving my head pointer
                   head->data = np->data;                  //Assigning new Data to the head pointer
                   head->next = temp;                      //Assigning the rest of the linked list back into head.
                   cout << "Making into creating the first node again, having to reassign." <<endl;
               }
               else{
                    //Searching where to place the node.
                    while(temp->data.priority > np->data.priority) //Searching if the next priority is higher then the passed.
                    {
                        cout << "Inside the while loop: " << np->data.priority << " versus "<<temp->data.priority <<endl;
                        if(temp->next == NULL)
                            break;
                        temp = temp->next;
                     }

            if(temp->next == NULL && np->data.priority < temp->data.priority) //Inserting at the end.
            {
                cout << "Making into creating the last node" <<endl;
                tail->next = np;
                cout << "Passing the function of creating the last node" <<endl;
            }
            else   //Inserting into the middle of the function.
            {
                cout << "Inserting in the middle of the queue" <<endl;
                np->next = temp->next;
                temp->next = np;
            }
        }
    }
}



void PQueue::dequeue(){
    if(empty()){
        cout << "\nAttempt to remove from an empty list." << endl;
        exit(1);
    }

    Person hold = head->data;
    NodePtr temp = head;
    head=head->next;
    if (head == NULL) tail = NULL;
    free(temp);
}

Person* PQueue::front(){
    //Person &temp = head->next->data;
    //Person &temp = head->data;
    Person &temp = head->data;
    return &temp;
}

Person* PQueue::back(){
    if(empty()){
        cout << "\nNo entries in list." << endl;
        exit(1);
    }
    Person &temp = tail->data;
    return &temp;
}

int main() {
    cout << "Starting main" << endl;
    PQueue queue1; //Creating my queue.
    cout << "Created Queue" << endl;
    Person tempPerson;
    ifstream inFile;
    inFile.open("/tmp/temp");
    cout << "going into while loop" << endl;

    while (inFile >> tempPerson.priority >> tempPerson.name){
        cout << "The priority is " <<  tempPerson.priority << " the name is " << tempPerson.name <<endl;
        queue1.enqueue(&tempPerson);
    }


    //Testing Section, trying to get .front and .back to work.
    Person *testPerson;
    testPerson = queue1.front();
    cout << "The TEST priority is " <<  testPerson->priority << " the TEST name is " << testPerson->name <<endl;
    /**
    Person *tailPerson;
    testPerson = queue1.back();
    cout << "The TEST priority is " <<  tailPerson->priority << " the TEST  name is " << tailPerson->name <<endl;
    **/

    queue1.dequeue();
    queue1.dequeue();
    queue1.dequeue();


    return 0;
}

原文：https://stackoverflow.com/questions/36096133