Thread: problme with ordered linked list

Hii all,
I am new in advance programming. I have a problme of generating 1,000,000 random number using rand() and inserting only 1 to 49 numbers in ordered listed list.
I m getting segmentation fault error.
When I put comment at insertevent(current,event) function, code runs fine. So problme is with insertevent function defination only.

Here is my code..

Code:

#include <stdio.h>
#include <stdlib.h>
typedef struct olnode olnode;
struct olnode{
      int eventnr;
      int eventfq;
      struct olnode * next;
};
olnode * getnode();   // these prototypes not necessary to define
int nextevent();
int main(void){
    olnode * head;
    olnode * current;
    int i,j, event;
    head=getnode();
    current=head;
                                                     // insert item into HEAD
    srand(time(NULL));
    do{
           if(event <=49 && event >=0)
              j=1;
           else
              j=0;
    }while(j==0);
    current->eventnr=event;         //inserting
       for(i=0;i<=1000000;i++)      // generate 1000000 numbers
   {
        event=nextevent();      // generate nextevent .... CALLING //  NEXTEVENT()
        if(event<=49 && event>=0)// make sure that next event is between 0..49
           {
                                //insert into list
                 temp=insertevent(current,event);
 }
   }
     current->next=NULL; 
  return(0);
}
   // get new node
olnode * getnode()
{
  olnode *NODE;
  NODE=malloc(sizeof(olnode));
  if(NODE==NULL){
    printf("\n malloc() failed \n");
    exit(0);
  }
 return NODE;
}
          
                                //generate new event
int nextevent()
{
   int temp;
   temp=rand();
                                
   return temp;
}
                                //insertevent into list
  
int insertevent(olnode *current, int event)
{
    current = getnode();
    current=current->next;
 
    current->eventnr=event;
          
    return 1;
}

-----------------------------------------------------
Apart from this I have to keep the order of number. Means myoutput should look like.
evennr eventfq (declared in struct)
32 76 | 23 34 | 9 56
(Means 32 number repeated 76 times.
23 number repeated 34 times and
9 number repeated 56 times)
I have only 2 days to finish the code. I hope I would get help from you guys.
Thanks in advance.

Originally Posted by palku

Code:

    do{
           if(event <=49 && event >=0)
              j=1;
           else
              j=0;
    }while(j==0);

This loop does the same thing as the single line j = 1;, does it not? Also, event has not yet been initialised. You must have some confusion here.

Originally Posted by palku

Code:

    current->eventnr=event;         //inserting

At this point in time, event has not yet been initialised. So you are filling eventnr with junk bits.

Originally Posted by palku

Code:

                                //insertevent into list
  
int insertevent(olnode *current, int event)
{
    current = getnode();
    current=current->next;
 
    current->eventnr=event;
          
    return 1;
}

Why do you have current as an argument to the function if you overwrite the function's copy of the pointer with the location of a freshly allocated node? Then current contains the memory address of an uninitialised, but allocated space in memory. Then you try changing the value of current to equal current->next. But current->next, a value in an uninitialised node, is an arbitrary group of junk bits. Then you try treating these junk bits as the memory address of a node by assigning to a value in this garbage memory location. This is where your segmentation fault happens.

But that is not the only problem. Major portions of your program make no sense at all. Think about what you are doing and make sure you understand completely what is going on.

Thanks a lot. I know there is lot of junk values. I m working on it. I wanted to have idea and thanks a lot for your suggestion.

I really appreciate it.
I ll try my best and post again if there is any problem.

// Hii all thanks a lot for helping me. spl. Rashakil Fol and Salem.
I m able to insert event into list. Now problme is when I try to print values in link list it gives me error..
..segmentation fault..

HERE IS MY REVISED CODE

Code:

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

typedef struct olnode olnode;

struct olnode{
        int eventnr;
        int eventfq;
        struct olnode * next;
};

olnode *list;
olnode *ptr;
olnode onode;
   
olnode * getnode();            
int nextevent();                
int insertevent(olnode *current, int);
void displayevent(olnode *current);
   
int main(void){
                                
   olnode * NODE;
   olnode * head;                 // Header node
   olnode * current;              // Current node
   int i,event=0,count,temp=0,j=0;

   head=getnode();              // Memory is allocated for HEAD
   current=head;                  // Current pointer pointing to HEAD
   srand(time(NULL));           // Seed the random number
                                            // Create an event for head
   do{
        event=rand();
        if(event <=49 && event >=0)
          j=1;
        else
          j=0;
   }while(j==0);
   
   current->eventnr=event;      // assign event to the HEAD OF CURRENT
   
   for(i=0;i<10000;i++)         // generate 1000000 numbers
   {    
        event=nextevent();      // generate nextevent 
        if(event<=49 && event>=0)// next event is between 0..49
           {
                printf("\nEvent is : %d.. and ",event);
                temp=insertevent(current,event);
                if(temp == 1)                                
                        printf("succcess");
           }  
   }
   current->next=NULL;          //end of list
        
   current=head;                //get the first node in order to DISPLAY
   printf("\nfirst number in list is %d   ..", current->eventnr);

    
/************************* here my segmentation fault occurs *********/
   
   current=current->next;
   printf("\nsecond number inlist is %d",current->eventnr);
        
   printf("\n");
   return(0);
}
   
                                // allocate memory for newnode
olnode * getnode()
{   
  olnode *NODE;
  NODE=malloc(sizeof(olnode));   //memory allocation   
  if(NODE==NULL){
    printf("\n malloc() failed \n");
  exit(0);
  }

int nextevent() 
{
   int temp;
   temp=rand();                 
                                
   return temp;   
}   
                                //insertevent into list
  
   
int insertevent(olnode *current, int event)
{
    current->next = getnode();
    current = current->next;
 
    current->eventnr=event;
    printf(" .. the value in linklist is : %d ", current->eventnr);
                                
    return 1;   
}