Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.std.c
Subject: A constant question
Message-ID: <8038@june.cs.washington.edu>
Date: 28 Apr 89 18:52:54 GMT
Reply-To: pardo@uw-june.UUCP (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 44

This is a `how do I do this in dpANS C' question.

I have a structure that contains pointers to other structures.

	struct container_t {
	    struct adt_t *x;
	    struct other_stuff x;
	};

I have defined some accessor functions, including an initialization
function.  The init function takes a pointer to a struct adt_t and
squirrels it away in the struct container_t.  The init function does not
change what the adt_t points at.  Suppose that my initial attempt at
defining a prototype looks like

	    extern void
	init (struct container_t *dest, struct adt_t squirrel);

Somebody else might get a handle on
the struct adt_t, and change it.  Thus,

    * `init' does not change the `struct adt_t'.
    * `struct container_t' is never used directly to change the `struct
      adt_t'.
    * The `struct adt_t' may change from time to time.

I am wanting to make the following declaration:

    "`init' does not change what it's parameter points at."

The struct container_t does not take a const pointer, so I can't declare
`squirrel' as a const-qualified parameter.  I could change the struct
container_t to have a const pointer, but that is incorrect because the
pointed-to storage might change over the lifetime of the container_t.

How should I declare `init'?


Thanks!

	;-D on  ( A volatile topic )  Pardo
-- 
		    pardo@cs.washington.edu
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