Question

所以我正在创建一个包含3个节点的链表，现在我正在尝试实现一个在C中显示列表的函数，这里是代码：

struct node *createList(struct node *start)
{
    int i, n, data;


    printf("Enter the number of nodes :  ");
    scanf("%d", &n);

    if (n==0)
        return start;

    printf("Enter the first element to be inserted :  ");

    scanf("%d", &data);

    printf("%d",data);

    start=insertInBeginning(start, data);

    for(i=2; i<=n; i++)
    {
        printf("Enter the next element to be inserted : ");
        scanf("%d", &data);
        insertAtEnd(start, data);
    }
    return start;
}

// end of createList


struct node *insertInBeginning(struct node *start, int data) 
{
    printf("we in begining \n");

    struct node *new_node,*current;

    printf("declared nodes");

    new_node = &data;

    printf("got new_node data \n");

    if(start == NULL) {

        printf("start is null! \n");

        start = new_node;

        current = new_node;

    } else {
        printf("start isn't null!  \n");

        new_node->link=start;

        start=new_node;
    }

}

//end of insertInBeginning


void insertAtEnd(struct node *start, int data)
{
struct node *new_node,*current,*temp;

new_node->info = data;
if(start == NULL)
 {

start= new_node;
current= new_node;

} else 
{
    temp = start;

    while(temp->link!=NULL) {
        temp =  temp->link;
    }
    temp -> link = new_node;
}


}

// end of insertAtEnd



void displayList(struct node *start)
{

    printf("we in displaylist");
    struct node *temp;

    temp = start->link;
    printf("temp has start values?");

    if(temp = NULL)
    {
    printf("we null now \n");
    } else {
    printf("we NOT null \n" );
    while(temp!=NULL) 
    {
    printf("%d \n",temp->info);
    temp = temp->link;
    }
}
}

我遇到的问题是显示函数中的循环完成但是它没有打印任何值，但我知道temp不是NULL所以它显示的东西，只是不是我想要的，是无论如何要解决这个问题？

Answer 1

这里有两个大问题：首先，（正如Martin James指出的那样），你没有从insertInBeginning（）例程返回，所以start设置为某个未定义的值。您还遇到一个巨大的问题，即您只是将int data投射到node *。您必须为新节点安装malloc（）内存并将数据写入其中。（然后返回它）你在insertAtEnd（）例程中遇到了同样的问题 - 你必须使用malloc（）内存来保存新节点。

static struct node *
insertAtStart (struct node *start, int data)
{
    struct node *new;

    new = malloc(sizeof(*new));
    if (new == NULL) {
        perror("malloc");
        exit(1);
    }

   new->value = data;
   new->next = start;
   return new;
}

static struct node *
insertAtEnd (struct node *start, int data)
{
    struct node *cur, *new;

    // create the node * we will be adding.  (This really ought to have been done
    // in the calling routine, so the same code would be used to create the node
    // entry and to store the value.  Note a big issue with this simple a struct,
    // but more complex structs really ought to only be created in one place, so
    // when they change, you won't have bugs where you forget to change one of 
    // the creation locations)
    new = malloc(sizeof(*new));
    if (new == NULL) {
        perror("malloc");
        exit(1);
    }
    new->value = data;
    new->link = NULL;

    // if this is going to be the only entry in the list, just return that it 
    // is the new start
    if (start == NULL) 
        return new;

    // find the last entry
    for (cur = start ; cur->link != NULL ; cur = cur->link)
        ;
    cur->link = new;
    return start;
}

你真的想打开编译器警告 - 它可以节省大量时间让编译器告诉你这些错误。如果您正在使用gcc，请在编译命令中添加-Wall -Werror（如果您使用的是其他编译器，则需要阅读手册页。）

（还有其他gcc警告可以打开，但是-Wall会为你提供很多有用的警告。你可以阅读手册页找到你想要的所有内容，如果你想打开更多）

Answer 2

如上所述，插入功能有一些麻烦。此代码声明结构node 一次：

#include<iostream>
#include<fstream>
using namespace std;
struct node{int info; node* next; node(int a=0, node* b=0){info=a; next=b;}}; // field1->value field2->next node

此“声明”保证创建的节点具有已定义的值。创建具有暗淡值的简单列表的函数：

node* build_L(int dim)
{
 if(dim)
   {int x; cin>>x; return new node(x,build_L(dim-1));}
 return 0;
}

打印：

 void pr_L(node*L)
{
 if(L)
  {cout<<L->info<<' '; pr_L(L->next);}
 else
   cout<<endl;

}

在开头添加节点：

node*insB(node*L,int k)
{
  node* n=new node(k,L);
  return n;
}

最后：

 node* insE(node*L, int k)
            {
            node*temp=L;
            while(L->next)
            {
            L=L->next;
            }
            node*e=new node(k,0);
            L->next=e;
            L=temp;
            return L;
            }

在main中，您可以调用函数：

 main()
    {
       int dim_list;//set the number of nodes 

       cin>>dim_list;
    //or scanf()
       node*L=build_L(dim_list);

       cout<<"List built"<<endl;
    //or printf() 

    pr_list(L);
   int k,f; cin>>k;
    L=insB(L,k);
    cout<<"node in first position: "<<endl;
    pr_L(L);
    cin>>f;
    L=insE(L,f);
    cout<<"node in queue: "<<endl;
    pr_L(L);
    }

C：无法显示链接列表值

2 个答案: