Question

我正在检查构造函数中头节点的数据及其确定，但是当我在函数中检查它时它就消失了。为什么这个幽灵这个指针？

队列标题

E/Web Console﹕ Uncaught TypeError: Object #<Screen> has no method 'lockOrientation'

队列类

#ifndef QUEUE_H
#define QUEUE_H
#include "Node.h"
#include "LinkedList.h"

class Queue
{
    public:
        Queue();
        ~Queue();
        void addTail(Node* newNode);
        Node* deleteHead();
        int isEmpty();
        void PrintQueue(char* outName);

    protected:
    private:
        Node* head;
        Node* tail;
        LinkedList* myList;
};

#endif // QUEUE_H

主要功能

#include "Queue.h"

Queue::Queue()
{
    //constructor
    myList =  new LinkedList();
    head = myList->getHead();
    std::cout<<" head here is " << head->getData()<<std::endl; //
    std::cout<<" next after head is " << head->getNext()->getData()<<std::endl; //
    tail = myList->getTail();
}

void Queue::addTail(Node* newNode)
{
    std::cout<<"inserting before tail (queue)"<<std::endl;
    std::cout<<"new node is " << newNode->getData() <<std::endl;
    std::cout<<" head here is " << myList->getHead()->getData() <<std::endl;
    myList->insertLast(newNode);
}

Node* Queue::deleteHead()
{
    if(isEmpty()){
        std::cout<<"Queue is empty. Cannot remove anything anymore. Add more data to the queue!"<<std::endl;
        return head;
    }
    return myList->removeFirst();
}

int Queue::isEmpty()
{
    return myList->isEmpty();
}

void Queue::PrintQueue(char* outName)
{
    Node* cur = head->getNext(); //store current node to keep track. Set it to one after the head
    std::ofstream outfile;
    outfile.open(outName, std::ios::app);
    outfile << "Printing the values of the queue: ";
    std::cout<<"Printing the values of the queue: "<<std::endl;
    while(cur != tail)
    {
       std::cout<< cur->getData()<<", "<<std::endl; //print to the console
       outfile << cur->getData() <<", "; //print to file
    }
    outfile.close();
}

Queue::~Queue()
{
    //destructor
    delete myList;
}

链接列表

#include <iostream>
#include <fstream>
#include <string>
#include "Stack.h"
//#include "Stack.cpp"
#include "LinkedList.h"
//#include "LinkedList.cpp"
#include "Node.h"
//#include "Node.cpp"
#include "HashTable.h"
//#include "HashTable.cpp"


using namespace std;

int main( int argc, char* argv[] )
{
   //specifying the in and out files
    char* inFileName = argv[1];
    char* outFileName = argv[2];


    std::fstream infile (inFileName) ; // input file
    //open the input file and find largest integer
    int num;
    int largest = 0;
    Stack * myStack = new Stack();
    char buffer[33]; //create a buffer for using with itoa
    std::ofstream outfile;
    outfile.open(outFileName);

    if ( !infile.is_open() ) //check if input file is open
      cout<<"Could not open file\n";
    else {
        while (infile >> num) { // read file int by int and check if current is not the largest
            if(num > largest) largest = num;
            Node *newNode= new Node(itoa(num,buffer,10));
            myStack->push(newNode);
        }
    }
    std::cout<< std::endl;
    infile.close(); //close files that you read to avoid memory leaks

    myStack->PrintStack(outFileName);

    HashTable* hashBrown = new HashTable();

    int currentDigit = 0;
    int currentTable = 0;
    int numOfDig =0; //stores number of digits of the largest number
    string maxNum = itoa(largest,buffer,10);
    numOfDig = maxNum.length();
    std::cout<< "Num of digits " << numOfDig << std::endl;
    Node* current;
    while(!myStack->isEmpty())
    {
        current = myStack->pop();
        std::cout<< "pop from stack element " << current->getData() << std::endl;
        string str = current->getData();
        int index = atoi(&str.back());
        std::cout<< "insert at index " << index << std::endl;
        std::cout<< "inserting data: "<< current->getData()<< " at index:" << index << std::endl;
        hashBrown->myQueues[index].addTail(current);

    }
    hashBrown->printHashTable(outFileName);


    delete myStack;
    delete hashBrown;

    outfile.close();
    std::cout<< "finishing program " << std::endl;
    return 0;

}

所以一切正常，直到它尝试访问Queue的addTail（）函数中的头部或其数据。

Answer 1

您可以使用gdb调试程序，查找错误并修复它们。如果程序有核心，您可以使用backtrace来查看导致核心的原因。

在您认为程序行为连线的行处设置断点，您也可以让程序一步一步运行。
运行程序并打印变量值以查看是否需要变量值。如果变量是指针，您还可以打印它引用的内容。

简短的gdb tutorial

C ++中奇怪的段错误

1 个答案: