Path: utzoo!attcan!uunet!aplcen!samsung!usc!ucsd!ucbvax!ANDREW.CMU.EDU!gk5g+
From: gk5g+@ANDREW.CMU.EDU (Gary Keim)
Newsgroups: comp.soft-sys.andrew
Subject: Re: problems with menulists
Message-ID: <Qb7qn2K00VsWIIlYVX@andrew.cmu.edu>
Date: 19 Oct 90 21:14:42 GMT
References: <Ib7mI7C0M2YtMA68M1@thumper.bellcore.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 48

Excerpts from internet.info-andrew: 19-Oct-90 Re: problems with
menulists Nathaniel Borenstein@thu (1537)

>  I'm not really sure
> how your code managed to get the menu to show up at all, nor am I sure
> why it core dumped when you selected it, but I'd recommend, as a first
> pass to fixing it, that you try moving your ChainAfter into a PostMenus
> method.

The menu appears because textview doesn't ever clear it's menus chain
(menulist_ClearChain).  

The reason it was core-dumping was that the menulist->object (set via
menulist_DuplicateML, menulist_Create, or menulist_SetView) field wasn't
set and at some point in the enqueueing of the menu event this routine
is called:

boolean class_IsType(testobject, typeobject)
    struct basicobject *testobject, *typeobject;
{
    struct classinfo *testtype = testobject->methods->info;

    do {
        if (testtype == typeobject->methods->info)
            return TRUE;
/* Check for both NULL and "" superclassname because class generates "",
 * but should be fixed. */
        if (testtype->superclass == NULL && testtype->superclassname !=
NULL && *testtype->superclassname != '\0')
            if ((testtype->superclass =
class_Load(testtype->superclassnamekey)) == NULL) {
                    fprintf(stderr, "Could not load class %s.\n",
testtype->superclassname);
                    exit(1);
            }
        testtype = testtype->superclass;
    } while (testtype != NULL);

    return FALSE;
}

with these arguments:

class_IsType(menulist->object,proctable_entry->type)

So, you can see that a NULL pointer is dereferenced.

Gary