Definition of 'evaluate'

[Old Wolf]

Does the standard define the meaning of 'evaluate' ? Someone
in another newsgroup said they thought evaluating a pointer
meant dereferencing it, and I couldn't find any text to contradict
this.

 

[Alf P. Steinbach]

* Old Wolf:

Does the standard define the meaning of 'evaluate' ? Someone
in another newsgroup said they thought evaluating a pointer
meant dereferencing it, and I couldn't find any text to contradict
this.

The standard defines "used" in terms of appearance in a "potentially
evaluated" expression, in §3.2/2. The term "evaluate" is not explicitly
defined, as far as I can see. But it means to produce a single value or
reference of the type of the expression, and is implicitly defined that
way by the usage of "evaluation" in §5 (Expressions).

For a pointer variable p, the id-expression p evaluates the pointer,
producing its value. This contradicts the notion that evaluation
necessarily involves dereferencing.

The dereferencing expression *p also evaluates the pointer.

 

[Andrew Koenig]

Does the standard define the meaning of 'evaluate' ? Someone
in another newsgroup said they thought evaluating a pointer
meant dereferencing it, and I couldn't find any text to contradict
this.

If evaluating a pointer meant dereferencing it, the following code fragment
would have undefined behavior:

int* p = 0;
int* q = p;

because (a) initializing q requires evaluating p and (b) dereferencing a
zero pointer evokes undefined behavior.

 

[Michael DOUBEZ]

Andrew Koenig a écrit :

If evaluating a pointer meant dereferencing it, the following code fragment
would have undefined behavior:

int* p = 0;
int* q = p;

because (a) initializing q requires evaluating p and (b) dereferencing a
zero pointer evokes undefined behavior.

That was a question I had (I didn't remember it):
3.5.4.2 note 4
The effect of using an invalid pointer value (including passing it to
adeallocation function) is undefined.

Is returning a pointer value actually 'using it' ?

The relevant example was:
int* f()
{
return reinterpret_cast<int*>(0x42424242);

}
Is calling f() UB because it returns an invalid pointer or is it just
using/deferencing the returned value that is UB ?

Michael