[basic.compound] Clarify a pointer to a non-first element object of an array #6432
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| @@ -5383,6 +5383,8 @@ | |||
| after the end of the storage occupied by the object, | |||
| respectively. | |||
| \begin{note} | |||
| A pointer to an actual array element object is categorized as a pointer to an object, | |||
| even though it also points past the end of the previous array element, if any. | |||
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Do not get what does
it also points past the end of the previous array element
mean.
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I think this is as clear (or unclear) as "a pointer past the end of an object". Do you have better phrase for "the previous array element"?
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I think this is as clear (or unclear) as "a pointer past the end of an object"
You mean a pointer to an array element is also a pointer past the end of the previous array element?
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I think this is as clear (or unclear) as "a pointer past the end of an object"
You mean a pointer to an array element is also a pointer past the end of the previous array element?
I think we can surely say a pointer that is "a pointer past the end of an object" points past the end of some given object. (Isn't this a tautology?) And then, given T a[2], there're two choices:
- there's a pointer value pointing past the end of
a[0], and if so,a + 1is exactly that value; or - there's no pointer value pointing past the end of
a[0].
Personally, I think choice 1 makes a little more sense. But if you think choice 2 makes more sense, we may abandon this PR and clarify with that choice.
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According to [expr.add], a + 1 points to 1st array element. It can't be pointer past 0th at the same time, because Every value of pointer type is one of the following
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According to [expr.add],
a + 1points to 1st array element. It can't be pointer past 0th at the same time, because Every value of pointer type is one of the following
Well, I think we agree on that a + 1 is categorized as a pointer to an object, and I don't think a + 1 is the "pointer past 0th" (Isn't this the content of this PR?).
What I wanted to clarify is that a + 1 points past the end of a[0] without being the pointer past the end of a[0].
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a + 1points past the end ofa[0]
And this is my question: what does this mean
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And this is my question: what does this mean
IMO when p points to an object o, we can generally say p + 1 points past the end of o (perhaps some base class subobjects should be excluded).
Such a pointer is categorized a pointer to an object, even if it may also point past the end of the previous array element. That is, [basic.compound]/3.1 applies first whenever possible.
I think we can just make clarification in the note.
Fixes #4784.
Fixes cplusplus/CWG#385.