From:	Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: ...but
Date:	11 Aug 2000 13:07:36 GMT
Organization:	Aachen University of Technology (RWTH)
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Vermin <ratspl AT hotmail DOT com> wrote:
> but is it possible to have an array (or a pointer to an array) which doesn't
> have a a given size (or doesn't really exist) until you define it by making
> space for it in the mem...

That's exactly what pointers and 'new' (or malloc(), if you're writing
C instead of C++) are for.

If you want to do that in a subroutine, it needs that pointer passed
in by reference, so the pointer itself can be modified. I'm not
footsure with the C++ 'reference argument' thingy, so I'll explain how
it'd be done in C. There, pass-by-reference is implemented via another
level of pointer:

> some pseudo code:

> procedure proc1(pointer pp){
>   pp (points to) new array[arraySize];
> }

This would be

   void proc1(type **pp) {
	size_t arraySize;

	/* calculate arraySize, somehow */
	*pp = malloc(arraySize * sizeof(*pp))

	// C++-style would look like this:
	// *pp = new type[arraySize];
   }

> main(){
>   pointer p1;
>   call proc1(p1);
> }

and this:

    int main(void) {
	type *p1 = NULL;

	proc1(&p1);
    }

An alternative approach would be to have proc1() return a 'type *' as
its result. But that only works for *one* result per function, as
usual.
-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.

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