Wednesday, May 19, 2010

(unwrapped) pointer assignment -- double-pointer scenario 2 again

Before looking at double-pointers, let's clarify the basic rules. For regular pointers p and q2, (assuming 32-bit),
Rule 1) Foo *p = 0; p = ... // pointer p bitwise state change i.e. reseating
Rule 2) *q2 = ...// pointer q2 still points to the same pointee, but pointee's state changed via assignment operator (possibly overloaded)

Now, in http://www.parashift.com/c++-faq-lite/const-correctness.html#faq-18.17 shows a double pointer
Foo **q = &p; // q points to the address of pointer p

*q = ... // q still points to the same 32-bit object, which is pointer p, but p's content is changed, i.e. p reseated. Means the same as "p = ..."
Now we are ready for

Rule 3) SomeType * ptr = ... // ptr seating at initialization. This looks like Rule 2 but is really more like Rule 1.

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