How to sort a linked list like this?

The first thing is that there is some problem in the createlista() function as it creating a list with only one node .. u need a loop to add more nodes.

One solution of ur problem can be that whenever u add a new record in the list u add it at a position such that the resultant list is always sorted. If u do this way ur problem is automatically solved.

Second solution , if u dont want to change the create list then u can adopt any of the sorting algorithm and modify it accordingly to suit linked lists.

Please let me know which solution will u go for so that i can help u further.

regards
ramesh

http://www.csc.ncsu.edu/eos/users/e/efg/210/s99/course_locker/www/Notes/Sorting/Code/

for help on sorting linked lists

thanks sarda_ramesh, the first solution is not a bad idea.. My future problem will be that i will have lot of these lists, and i need to make one out of them, and then order the whole one...
So I don't know if it is useful to order the partial lists alone. I will work on it for another while, will let you know!
mags2000

Sarda,

Excuse me, but if you look carefully at the function, he is creating a more than one element.  creatlista is being called recursively until a 0 is entered as the first element in the scanf.

Second the link you gave is for C++ code.  This is the C forum...

mags2000,

You do have a bug, though...

You define your structure as

struct p_list
{
   int n;
   char *nome;
   char *cognome;
   struct p_list *next;
};

Please note that both nome and cognome are pointers to strings - they reserve no memory for the strings themselves.

When you use scanf, you also use pointers to strings that have not been allocated - your program WILL crash.

I suggest the following...

Leave your struct definition alone.

In createlista, declare the temporary strings to be large enough to hold any name, say

char no[100];
char co[100];

then change the loop to be as follows:

if (a != 0)
   {
   head = malloc(sizeof(ELEMENT));
   head->n=a;
   head->nome=malloc(strlen(no)+1);
   strcpy(head->nome,no);
   head->cognome=malloc(strlen(co)+1);
   strcpy(head->cognome,co);
   head->next=crealista();
   }

You can't just set head->nome=no, because no is just a temporary variable on the stack - it disappears once the function returns...

If you can't use the C++ versions let us know, it is easy enough to sort a linked list in C.

One note on your code - you are returning the pointer to the last element in your list, fyi..

thank you gj62, in effect the crealista() is recursive and it works well with your suggestion!
I can't use C++, only C is available for sorting this list. I would prefer to use only one pointer to next, avoiding a previos pointer...

mags,

go to here:

http://www.snippets.org/snippets/portable/portable.php3

Download LL_MSORT.C and SNIPSORT.H.

You need to make only a few modifications:

In SNIPSORT.H, replace your struct for the list_struct.

In LL_MSORT, change the compare rountine to:

/* returns < 0 if *p sorts lower than *q */
int keycmp (list *p, list *q)
{
      if (strcmp(p->cogname, q->cogname)==0)
      {
        if (p->a > p->q) return(1);
        return(-1);
      }

      return strcmp(p->cogname, q->cogname);
}

This should do the trick - remember, strcmp is case sensitive - if you need case insensitive, let me know...

you did it! Thanks a lot gj62, I was near a solution like your one, but this is better!
mags