Subject: MP1

(This message is being sent to all CPSC 102 Sec 1 students )

A student asks:

So how do I refer to tpln in other function?
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Dr. Westall was unclear on the nature of what "other function"
meant but assumed it meant functions that were passed a pointer
the object_t structure.

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The student continued:

I tried ie "
obj->priv->priv->dimension[0] " but I still get the
dereferencing warnings and errors, even after casting tpln to
void.

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Dr. Westall sez:

Massive pointer chains always lead to MASSIVE DISASTER .
Many students (not you) tried this unsuccessfully on the
material_getbyname() problem on the midterm.

One step at a time wins EVERY TIME ITS TRIED.

Assuming obj points to a legit object_t and you declare

plane_t   *pln;
tplane_t *tpln;

then

pln = (plane_t *)obj->priv;
tpln = (tplane_t *)pln->priv;
xdim = tpln->dimension[0];

will recover you a correct pointer to the tplane_t and access the
x dimension.

It is also POSSIBLE to formulate a correct  but IMHO
simply AWFUL solution using your proposed approach
by embedding needed casts and doing something like
(this CAN be made to work but I haven't tested this formulation).

xdim = (((tplane_t *)((plane_t *)obj->priv)->priv)->dimension[0]

Furthermore with my approach I can step through this with
gdb and at each step do:

print *obj
print *pln
print *tpln

With the cascading pointer "solution" you (AND I) have no
clue where it ALL FELL TO PIECES.