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[conv.lval] Fix cross-reference for 'invalid pointer value' #5886

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[conv.lval] Fix cross-reference for 'invalid pointer value' #5886

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[conv.lval] Fix cross-reference for 'invalid pointer value'
blackteahamburger Oct 4, 2022
8f2856a
[basic.compound]/3.4 add cross reference to [basic.stc.general]
blackteahamburger Mar 11, 2023
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2 changes: 1 addition & 1 deletion source/basic.tex
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Expand Up @@ -5240,7 +5240,7 @@
the \defnx{null pointer value}{value!null pointer} for that type, or
\item
\indextext{invalid pointer value|see{value, invalid pointer}}
an \defnx{invalid pointer value}{value!invalid pointer}.
an \defnx{invalid pointer value}{value!invalid pointer}\iref{basic.stc.general}.
\end{itemize}
A value of a
pointer type
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2 changes: 1 addition & 1 deletion source/expressions.tex
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Expand Up @@ -666,7 +666,7 @@
the glvalue.

\item Otherwise, if the object to which the glvalue refers contains an invalid
pointer value\iref{basic.stc.dynamic.deallocation}, the behavior is
pointer value\iref{basic.compound}, the behavior is
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@tkoeppe tkoeppe Mar 12, 2023

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What about here, shouldn't this also refer to basic.stc.general for the definition of "invalid pointer"? Why is basic.compound a good reference?

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@blackteahamburger blackteahamburger Mar 19, 2023 •
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What about here, shouldn't this also refer to basic.stc.general for the definition of "invalid pointer"? Why is basic.compound a good reference?

But [basic.stc.general]/4 specifies how to form an invalid pointer value, while [basic.compound]/3.4 is the definition (so [basic.stc.general]/4 refers to [basic.compound]/3.4).

And I think

Indirection through an invalid pointer value and passing an invalid pointer value to a deallocation function have undefined behavior. Any other use of an invalid pointer value has implementation-defined behavior.

in [basic.stc.general]/4 should be better placed in [basic.compound]/3. But [basic.compound]/3 may need to be split because it is too long.

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@tkoeppe tkoeppe Aug 16, 2023

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Sorry, could you explain a bit how basic.general is the definition? I don't see "invalid" mentioned in basic.general except for in that list in p3 (which doesn't seem like a definition?) and in notes.

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@jensmaurer jensmaurer Aug 16, 2023

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[basic.compound] p3 contains the taxonomy of pointer values. It states "there exists a pointer value that is an invalid pointer value".

[basic.stc.general] p4 tells us about one way how to obtain an invalid pointer value (maybe there are others). It also explains a bit of the semantics of an invalid pointer value, but this should probably be moved elsewhere in the long run. For example, [conv.lval] p3.3 tells us a little more about an invalid pointer value.

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@tkoeppe tkoeppe Aug 16, 2023

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Yes, right. In fact, [conv.lval] is the very subject of this PR. I'm not sure where the definition of invald value could be moved to improve the presentation; isn't basic.stc.general a good place? We could just add a cross reference to it from [basic.compound]/(3.4).

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@jensmaurer jensmaurer Aug 16, 2023

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Sure, but that's converted to use "operator*" (expr.ref p2 and expr.mptr.oper p3).

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@jensmaurer jensmaurer Aug 16, 2023

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Maybe the last two sentences of [basic.stc.general]p4 should become a note?

Except that we seem to lack normative statements elsewhere.

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@tkoeppe tkoeppe Aug 16, 2023

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Yes, the normative wording would have to move somewhere more appropriate.

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@jensmaurer jensmaurer Nov 8, 2023

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CWG2822 moves the normative wording "somewhere else", for unrelated reasons.

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@tkoeppe tkoeppe Nov 8, 2023

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Shall we wait for that to land then?

\impldef{lvalue-to-rvalue conversion of an invalid pointer value}.

\item Otherwise, the object indicated by the glvalue is read\iref{defns.access},
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