i have some doubts on free function when i write a linked list.

here are my data structure:

typedef struct  listnode {
other_datatype    *data;
struct listnode     *next ;

} listnode_t ;

listnode_t    *listhead;
...
...

I write a freelist ( ) function to free memory when linked list is not
used. I want to free all memory ,  including the linked list self and
the data pointed by listnode_t.data.

1  void freelist () {
2  listnode_t  ptr =null ;
3  while( listhead!=null ) {
4        ptr = listhead;
5        listhead = listhead->next ;
6        free( ptr->data ) ;
7        free( ptr ) ;
8   }
9 }

why above code could not work?  when i remove the line 6 , compiler
report no error.
but the memory of ptr->data  was freed ? why?

thanks for help!

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jamesonang@gmail.com wrote:
> i have some doubts on free function when i write a linked list.
>
> here are my data structure:
>
> typedef struct  listnode {
>     other_datatype    *data;
>     struct listnode     *next ;
>
> } listnode_t ;
>
> listnode_t    *listhead;
> ...
> ...
>
> I write a freelist ( ) function to free memory when linked list is not
> used. I want to free all memory ,  including the linked list self and
> the data pointed by listnode_t.data.
>
> 1  void freelist () {
> 2  listnode_t  ptr =null ;
given the above declarations, the above should read
listnode_t *ptr = NULL;

Please post actual code.

> 3  while( listhead!=null ) {
> 4        ptr = listhead;
> 5        listhead = listhead->next ;
> 6        free( ptr->data ) ;
> 7        free( ptr ) ;
> 8   }
> 9 }
>
> why above code could not work?  when i remove the line 6 , compiler
> report no error.
Not that easy to guess. It should work.
What is the exact error the compiler tells you ?

> but the memory of ptr->data  was freed ? why?

What ?


> thanks for help!
>

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