分段故障链表

Question

I keep getting a segmentaion fault when trying to create a simple linked list.The problem seems to occur inside the print_list function.I've been trying to fix this for about an hour but it's still not working.I'd really appreciate your help.This is the code:

#include<stdio.h>
#include<stdlib.h>

struct node{
   double value;
   struct node *next;
   };
 struct node* getnode()
   {  
      struct node* create;
      create=(struct node*)malloc(sizeof(struct node));
      create->next=NULL;
      return create;
   }     


 void insert_at_beg(struct node*first,double x)
  {                                                     
      struct node*temp=getnode();
      if(!first)
      {
         temp->value=x;
         first=temp;
      }
      else
      { 
          temp->value=x;
          temp->next=first;
          first=temp;
      }
  }   
 void print_list(struct node*first)
  {    
       struct node*temp;
       temp=first;

       if(temp==NULL)
        { printf("The list is empty!\n");
          return;
          }

      while(temp!=NULL)
            if(temp->next ==NULL) // this is where i get the segmentation fault
            {  printf("%lf ",temp->value);
               break;
            }
            else
             { 
                printf("%lf ",temp->value);
                temp=temp->next;
             }

       printf("\n");
   }


   int main()
   {
       struct node *first;
       insert_at_beg(first,10.2);
       insert_at_beg(first,17.8);
       print_list(first);

       system("PAUSE");
   }

Answer 1

Make it return the new head of the list:

void insert_at_beg(struct node *first, double x)
{                                                     
      struct node *temp = getnode();
      temp->value = x;
      temp->next = first;
      return temp;
}

A bit simpler, too. :)

Then in main() , do:

   struct node *first = insert_at_beg(NULL, 10.2);
   first = insert_at_beg(first, 17.8);

Answer 2

You can use gdb - [GNU debugger]. It should help you to figure out where exactly the segmentation fault is. You can find more information in this link

Answer 3

You have an invalid address from the temp->next call. C does not default initialize variables you need to to set the first value to NULL

struct node* first = NULL;