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Question

我是c ++和编程的新手。我正在尝试实现一个双向链表。我认为列表已成功创建，但我无法完全打印列表。你能告诉我下面的printListForward方法有什么问题吗？我的代码尚未完成。非常感谢任何提示和建议。

#include "MagicSquare.hpp"
#include <iostream>

class MagicSquaresList{

private:

    struct MagicSquaresNode{

        int nodeIndex;
        MagicSquaresNode *pleft;
        MagicSquaresNode *pright;
        MagicSquaresNode *pup;
        MagicSquaresNode *pdown;
    };

    MagicSquaresNode *head;
    MagicSquaresNode *tail;

public:
    MagicSquaresList (){ 
        head = NULL;
        tail = NULL;
    }

    int getListLength(){
        int length = 1;
        MagicSquaresNode *temp = new MagicSquaresNode;
        temp = head;

        if(isEmpty()){
            return 0;
        }else{
            while(temp != tail){
                length++;
                temp = temp->pright;
            }
        }
        return length;
    }

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

    void appendToEnd(int val){
        MagicSquaresNode *newNode = new MagicSquaresNode;
        newNode->nodeIndex = val;

        if(isEmpty()){
            tail = newNode;
        } else {
            tail->pright = newNode;
            newNode->pleft = tail;
        }

        tail = newNode;
    }

    void printListForward() {
        MagicSquaresNode *ptr = head;

        while(ptr != tail){
            std::cout << ptr->nodeIndex << " ";
            ptr = ptr->pright;
        }

        std::cout << std::endl;
    }

};


int main(){

    /*********** temporary *****************/
    int matrixSize, listSize;
    matrixSize = 3;
    listSize = matrixSize * matrixSize;
    /****************************************/

    MagicSquaresList list1;

    for (int i = 1; i <= listSize; i++){
        list1.appendToEnd(i);
    }

    list1.printListForward();
    std::cout << list1.getListLength() << std::endl;
    return 0;

}

Answer 1

你需要设置头部。

  void appendToEnd(int val){
    MagicSquaresNode *newNode = new MagicSquaresNode;
    newNode->nodeIndex = val;

    if(isEmpty()){
        tail = newNode;
        head = newNode;
    } else {
        tail->pright = newNode;
        newNode->pleft = tail;
    }

    tail = newNode;
    }

Answer 2

只是一些评论。首先，您要使用适当的缩进。对于初学者来说，学习编写一个简单的Makefile非常重要。在你的情况下，我为你写了一个。

生成文件：

  1 bin_PROGRAMS=doublelink
  2 GCCLIBDIR= /usr/local/lib64
  3 CXXFLAGS=-g -std=c++11
  4 CC=g++   
  5 LDFLAGS=-L$(GCCLIBDIR)
  6          
  7 all : $(bin_PROGRAMS)
  8 
  9 doublelink : doublelink.o
 10    $(CC) $(CXXFLAGS) -o $@ $^ $(LDFLAGS)

对于您的源代码，我进行了简单的编辑并将文件命名为：doublelink.cpp：

//#include "MagicSquare.hpp"
#include <iostream>

using namespace std;

class MagicSquaresList{
   private:
      struct MagicSquaresNode {
         MagicSquaresNode(int ni) : nodeIndex(ni), pleft(0), pright(0), pup(0), pdown(0) { }
         int nodeIndex;
         MagicSquaresNode *pleft;
         MagicSquaresNode *pright;
         MagicSquaresNode *pup;
         MagicSquaresNode *pdown;
      };

      MagicSquaresNode *head;
      MagicSquaresNode *tail;

   public:
      MagicSquaresList () { 
         head = 0;
         tail = 0;
      }

      int getListLength(){
         MagicSquaresNode *temp = head;
         if (temp == 0) {
            return 0;
         }
         int length = 0;
         while (temp != 0) {
            ++length;
            temp = temp->pright;
         }
         return length;
      }

      bool isEmpty(){
         return head == 0;
      }

      void appendToEnd(int val){
         MagicSquaresNode *newNode = new MagicSquaresNode(val);
         if (tail == 0) {
            head = newNode;
         } 
         else {
            tail->pright = newNode;
            newNode->pleft = tail;
         }
         tail = newNode;
      }

      void printListForward() {
         MagicSquaresNode *ptr = head;
         while (ptr != 0) {
            //cout << ptr << endl;
            std::cout << ptr->nodeIndex << " ";
            ptr = ptr->pright;
         }
         std::cout << std::endl;
      }

};


int main(){
    /*********** temporary *****************/
    int matrixSize, listSize;
    matrixSize = 3;
    listSize = matrixSize * matrixSize;
    /****************************************/

    MagicSquaresList list1;

    for (int i = 1; i <= listSize; i++){
        list1.appendToEnd(i);
    }

    list1.printListForward();
    std::cout << list1.getListLength() << std::endl;
    return 0;
}

将两个文件都放在目录中，然后键入

请

二进制文件双链接将出现在您的目录中您通过键入其名称来运行此程序：

$ doublelink 1 2 3 4 5 6 7 8 9 9

但是所有这些努力。您永远不需要实现双链表。您应该使用C ++标准库并为您的目的自定义数据类型。 std :: list实现为双链表。请阅读http://www.cplusplus.com/reference/list/list/处的文件。你应该通过

创建你感兴趣的结构

list<MagicSquare> myfancySquareList;

myfancySquareList.push_back(MagicSquare(somevalue));

您的双链表也缺少析构函数，并且您有内存泄漏。您的实现中还有许多其他缺失的东西，通常由几百页的教科书涵盖。希望这能让你开始。遇到问题时，可以在调试模式下运行程序：gdb doublelink。您可以单步执行它并找出问题所在。您最初的问题是分段错误。尝试运行原始程序并查看它终止的位置。

打印双向链表 - 没有结果

2 个答案:

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