Dear suckless folks,
sorry, for being ignorant, but I have one question regarding the warning
below from Clang’s static analyzer scan-build.
```
dwm.c:480:4: warning: Use of memory after it is freed
unmanage(m->stack, 0);
^~~~~~~~~~~~~~~~~~~~~
```
The code [1], looks like below.
```
[…]
void
detach(Client *c)
{
Client **tc;
for (tc = &c->mon->clients; *tc && *tc != c; tc = &(*tc)->next);
*tc = c->next;
}
void
detachstack(Client *c)
{
Client **tc, *t;
for (tc = &c->mon->stack; *tc && *tc != c; tc = &(*tc)->snext);
*tc = c->snext;
if (c == c->mon->sel) {
for (t = c->mon->stack; t && !ISVISIBLE(t); t = t->snext);
c->mon->sel = t;
}
}
[…]
void
unmanage(Client *c, int destroyed)
{
Monitor *m = c->mon;
XWindowChanges wc;
/* The server grab construct avoids race conditions. */
detach(c);
detachstack(c);
if (!destroyed) {
wc.border_width = c->oldbw;
XGrabServer(dpy);
XSetErrorHandler(xerrordummy);
XConfigureWindow(dpy, c->win, CWBorderWidth, &wc); /*
restore border */
XUngrabButton(dpy, AnyButton, AnyModifier, c->win);
setclientstate(c, WithdrawnState);
XSync(dpy, False);
XSetErrorHandler(xerror);
XUngrabServer(dpy);
}
free(c);
focus(NULL);
updateclientlist();
arrange(m);
}
[…]
void
cleanup(void)
{
Arg a = {.ui = ~0};
Layout foo = { "", NULL };
Monitor *m;
size_t i;
view(&a);
selmon->lt[selmon->sellt] = &foo;
for (m = mons; m; m = m->next)
if (m->stack)
unmanage(m->stack, 0);
XUngrabKey(dpy, AnyKey, AnyModifier, root);
while (mons)
cleanupmon(mons);
for (i = 0; i < CurLast; i++)
drw_cur_free(drw, cursor[i]);
for (i = 0; i < SchemeLast; i++)
free(scheme[i]);
drw_free(drw);
XSync(dpy, False);
XSetInputFocus(dpy, PointerRoot, RevertToPointerRoot, CurrentTime);
XDeleteProperty(dpy, root, netatom[NetActiveWindow]);
}
[…]
```
Unfortunately, my C knowledge is not good enough to understand, why the
while loop is used here. Even reading the called functions, I don’t see
why `m->stack`, a pointer, should be checked in the while condition. Is
it set to `NULL` somewhere?
Thank you in advance.
Best regards,
Paul
[1] http://git.suckless.org/dwm/tree/dwm.c#n480
