🚀 go-pugleaf

I recently wrote a "generic" linked list sorter.  It assumes that
struct foo {
	struct foo *next;
};

is "compatible" with any structure beginning with a pointer
to itself.  I *believe* this is legal; there can be no initial padding, and I
seem to recall that pointer to struct is compatible with pointer to struct.

I am now doing a doubly-linked list sorter.  I am going to assume that, if
the user hands me a list looking like:

struct foo {
	struct { struct foo *next, *prev; };
	...
};

that it's compatible with my
struct bar {
	struct { struct bar *next, *prev; };
};
... I can go to "struct bar *next; struct bar *prev;" if needbe.

Here's where it gets ugly:

Can I assert that treating a struct bar as a struct foo will
work?  In other wordss, can I *legally* (Screw real-world compilers; I'm
writing for ANSI, not for a specific project) assert that a pointer to a
struct is good for referencing a first member of that struct *or*
for referencing the first member of a struct which is the first
member of that struct?

And if anyone can point me at a better way to say this in English,
I'd appreciate it.

(My plan is to simply use my sorting engine, which is mergesort based, to sort
the doubly-linked list as if it were a singly-linked list, then iterate
through correcting the prev pointers.)

-s
-- 
Peter Seebach - seebs@solon.com || seebs@intran.xerox.com --
C/Unix proto-wizard -- C/Unix questions? Send mail for help.  No, really!
Copyright 1995 Peter Seebach.  --  High energy particle theology
The *other* C FAQ - ftp taniemarie.solon.com /pub/c/afq