Function returning Structure: How does it work?

[Karl Heuer]

In article <8048 at crdgw1.crd.ge.com> larocque at jupiter.crd.ge.com (David M. LaRocque) writes:
>I think I must be missing something fundamental in the way
>storage allocation works.  I see how malloc() can return 
>"permanant" storage in memory that the caller knows won't
>get overwritten until free() is called, at least I think I 
>understand the K&R II description of their malloc routine (pg 185).
>However, in the above approach, how can a caller be sure that
>makepoint() returned memory that won't get trounced somehow?

The usual implementation is that the caller supplies the storage space.

>In addition if a point is no longer needed is there a method
>analagous to free() that can be used to return the point's
>memory to the operating system?

No need.  The caller knows when it's done with it (usually by the end of the
next operator).  Note that in
	struct point p;
	p = make_point(x, y);
the contents are being copied, not the address, so the temporary storage may
be reclaimed immediately afterwards (regardless of the lifetime of `p').

Karl W. Z. Heuer (karl at ima.ima.isc.com or harvard!ima!karl), The Walking Lint