Re: Ada Queue

[Hyman Rosen <hymie@prolifics.com>]

Ted Dennison <dennison@telepath.com> writes:
> In article <38ed0123@news.hamilton.edu>,
> For those who don't want to bother surfing there, the relevent source is:
> 
> listelement * AddItem (listelement * listpointer, int data) {
>     listelement * lp = listpointer;
>     if (listpointer != NULL) {
>         while (listpointer -> link != NULL)
>             listpointer = listpointer -> link;
>         listpointer -> link = (struct listelement  *) malloc (sizeof
> (listelement));
>         listpointer = listpointer -> link;
>         listpointer -> link = NULL;
>         listpointer -> dataitem = data;
>         return lp;
>     }
>     else {
>         listpointer = (struct listelement  *) malloc (sizeof
> (listelement));
>         listpointer -> link = NULL;
>         listpointer -> dataitem = data;
>         return listpointer;
>     }
> }
> 
> The reasons I think he probably did it this way are:
> 1, C has no "in out" parameters like Ada. In order to emulate them, he'd
> have to have used something like "listelement ** listpointer", a
> construction that is both ugly and error-prone.
> 2. C automaticly gives you a function return, which subtly encourages
> developers to find some use for it.
> In other words, I think his interface has more to do with the failings
> of C than anything else. This is a very good example of why its not
> generally best to do wrote translations of C code into Ada.

If I were writing this (and I have, many times), I would certainly use
the "error-prone" number 1. Using the function return value is fine -
we should return the newly allocated node. My C code would be

listelement *AddItem(listelement **linkpointer, int data)
{
	listelement *node;
	while ((node = *linkpointer) != 0)
		linkpointer = &node->link;
	if ((node = *linkpointer = malloc(sizeof(listelement))) != 0)
	{
		node->link = 0;
		node->dataitem = data;
	}
	return node;
}