Thread: use of uninitialized value of size 4.

Hi, I keep getting this error message for my code even though I initialized it already.

Code:

= Use of uninitialised value of size 4
=    at 0x80484D9: irest_destroy (ilist_destructive.c:55)
=    by 0x804865B: iprint (ilist_destructive.c:115)
=    by 0x80486F7: main (ilist_destructive.c:128)
=  Uninitialised value was created by a stack allocation
=    at 0x8048679: main (ilist_destructive.c:122)
= Use of uninitialised value of size 4
=    at 0x80484F4: irest_destroy (ilist_destructive.c:58)
=    by 0x804865B: iprint (ilist_destructive.c:115)
=    by 0x80486F7: main (ilist_destructive.c:128)
=  Uninitialised value was created by a stack allocation
=    at 0x8048679: main (ilist_destructive.c:122)
= Invalid read of size 4
=    at 0x80484D9: irest_destroy (ilist_destructive.c:55)
=    by 0x804865B: iprint (ilist_destructive.c:115)
=    by 0x80486F7: main (ilist_destructive.c:128)
=  Address 0x4 is not stack'd, malloc'd or (recently) free'd
= Process terminating with default action of signal 11 (SIGSEGV)
=  Access not within mapped region at address 0x4
=    at 0x80484D9: irest_destroy (ilist_destructive.c:55)
=    by 0x804865B: iprint (ilist_destructive.c:115)
=    by 0x80486F7: main (ilist_destructive.c:128)
=  If you believe this happened as a result of a stack
=  overflow in your program's main thread (unlikely but
=  possible), you can try to increase the size of the
=  main thread stack using the --main-stacksize= flag.
=  The main thread stack size used in this run was 16777216.

why is it doing that???!?

following is my code. this code should start at line 46.

Code:

ilist irest_destroy(ilist il){
   // modifies il to remove the first element, and returns the modified ilist
   // frees the memory associated with the first element
   // references to il cease to be valid ilists
   // the result (if non-empty) must eventually be consumed by one of:
   //     icons_destroy, irest_destroy, idelete
   if (il == NULL) return NULL;
   ilist r = il->rest;
   ilist head = malloc(sizeof(struct ilist_ADT));
   head->first = r->first;
   head->rest = NULL;
   ilist l_end = head;
   for (ilist a = r->rest; a != NULL; a=a->rest){
   ilist tmp = malloc(sizeof(struct ilist_ADT));
   tmp->first = a->first;
   tmp->rest=NULL;
   l_end->rest = tmp;
   l_end=tmp;
   }
   free(il);
   return head;
}

this is the structure definition used in the above code:

Code:

struct ilist_ADT{
  struct ilist_ADT *rest;
  int first;   
};

typedef ilist_ADT *ilist;

It might help if you showed the exact error message and pointed out the line that the line number refers to.

> = Address 0x4 is not stack'd, malloc'd or (recently) free'd
Yes, your pointer is NULL, and the member offset inside your struct is 4 bytes.

Which looking at your struct, corresponds exactly to "int first"

> = Invalid read of size 4
> = at 0x80484D9: irest_destroy (ilist_destructive.c:55)
> = by 0x804865B: iprint (ilist_destructive.c:115)
> = by 0x80486F7: main (ilist_destructive.c:128)
Start with line 55 of ilist_destructive.c