Passing pointers to structures

[Trent Tobler]

>From article <1991Jan19.055923.19423 at unicorn.cc.wwu.edu>, by n8743196 at unicorn.cc.wwu.edu (Jeff Wandling):
> 
> Example:
> 
> 	struct node {
> 		int key;
> 		};
> 
> 
> 	foo(h_ptr)
> 	struct node *h_ptr;              /*   ?? */
> 	{
> 		h_ptr->key=10;		/* anything */
>         }	
> 
> 
> 	main() 
> 	{ 
> 	      struct node *head;
> 
> 	      foo(head);  OR  foo(&head);   /* ?? K&R 1, p91 says use '&head'
> 					       but this isn't the same. Or is
> 			                       it?  */
> 	}
> 
> 
>   How do I pass the pointer? And in the function "foo", how do I
> access it? I want "head" to be passed by 'reference', but I don't know
>   I have K&R 1 in front of me and I checked the FAQ. If you can cite a 
> 

:::::::::::::::::::::::

If your purpose was to change the variable head (defined in main) to
point to some structure that is created/looked-up in foo:

You must declare foo() with ...

  foo(h_ptr)
	struct node **h_ptr;	/* h_ptr is the address of a pointer to node */

and access h_ptr with ...

	(*h_ptr) = get_head();		/* assign the pointer to some node */
	(*h_ptr)->key = key_value;	/* assign a key to the node */

and call foo with ...

  struct node *head;	/* this will contain the node pointer */
  foo( &head);		/* assign head to the node */

:::::::::::::::::::::::

If your purpose was different, that of simply affecting the elements
**IN** the struct node variable, then this is the format:

You must declare foo() with ...

  foo(h_ptr)
	struct node *h_ptr;	/* h_ptr is a pointer to a node */

and access h_ptr with ...

	h_ptr->key = key_value;	/* assign a value to the key element */

and call foo with ...

  struct node head;	/* declare some space to store key */
  foo( &head);		/* change a field in head */

> -- 
> jeff wandling | western washington university | inet: jeff at arthur.cs.wwu.edu
> cs ugrad      | bellingham, wa 98225 USA      |  n8743196 at unicorn.cc.wwu.edu

--
Trent Tobler    - ttobler at csulx.weber.edu