Linked List problem :(

Ok, here is the part that doesnt work :(

Obviously, i must be mistunderstanding something, so if you could point me in the right direction, that would be great :)

Code:

---

IORB list;
IORB *tail = &list;
.
.
IORB *temp = tail;
printf("%hd \n", tail->base_pri);
printf("%hd \n", temp->base_pri);

---

tail is declared as a pointer to an IORB list.
When running this code, the two lines produce different results. They (appear) to be (supposedly) pointing to the same thing, but obviously are not :(

Thanks :)

They should point to the same thing. Here's some sample code (note the format modifiers have changed

Code:

---

#include <stdio.h>
 
 typedef struct IORB
 {
  char *base_pri;
 } IORB;
 
 int main(void)
 {
  IORB list;
  IORB *tail = &list;
  IORB *temp = tail;
 
  tail->base_pri = NULL;
  printf("%p \n", (void*)tail->base_pri);
  printf("%p \n", (void*)temp->base_pri);
  tail->base_pri++;
  printf("%p \n", (void*)tail->base_pri);
  printf("%p \n", (void*)temp->base_pri);
 
  return 0;
 }
 
 /*
 Output
 
 00000000
 00000000
 00000001
 00000001
 
 */

---

Thanks Hammer.

That solved my problem somewhat... I have ended up starting my code from scratch again... I cant seem to add a node to the list. It was a problem in my code before as well, and i still cant figure it out.

Code:

---

#include <stdio.h>
 typedef struct iorb
 {
  short int base_pri;
  struct iorb *link;
 } IORB;


  IORB list;
  IORB *tail = &list;
  IORB *temp = tail;

#include "list.h"
 
 int main()
 {
  int menu;
  short int temp_pri = 0;
 
 
  tail->base_pri = 0;
 
  add(temp_pri);
  temp = tail;

  display();
 
  scanf("%d", &menu);
 
  return 0;
 }



//// list.h

int add(short int pri){
  IORB *node;
  tail->link = node;
  tail = tail->link;
  tail->base_pri = pri;
  tail->link = NULL;
  return 0;
}


int display(){
  IORB *temp = &list;
  while(temp)
  {
      printf("%hd\n", temp->base_pri);
      temp = temp->link;
  }
}

---

Sorry for posting it all. Its also messy because i couldn't get the passing to work between functions...

Anyway, when i run this code, it crashes. But if i take out the variable being passed to the add() function. ie:

Code:

---

int add()

---

then it works fine. :S Logic seems to be right, so its a runtime error... any ideas?

> IORB *node;
In add() you create a new node, but never allocate any memory for it.

node = malloc(sizeof( *node) );

ya! you need to allocate memory for the structure, before moving values.
the allocation may be node=(IORB *)malloc(sizeof(IORB *));
if you leave it, the node remains tangling. & junk memory gets allocated.

>> sizeof(IORB *)
This only allocates enough space for a pointer to IORB.
You want sizeof(IORB) or as previously posted, sizeof(*node).

gg