This is really a problem that arises *because* g++ implements the standard.
I have tried to raise this as a DR, but to no avail.
Subject: Defect Report: reference-compatible is defined too narrowly in
[decl.int.ref]
Date: Mon, 07 Feb 2005 17:33:41 +0000
From: Joern Rennecke <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
8.5.3 [decl.int.ref] Paragraph 4 defines reference-compatible so
narrowly that "const int * const" is not reference-compatible to
"int * const" . As a result, for this program:
extern void abort (void);
int i0 = 999;
int *const p = &i0;
const int *const &
foo ()
{
return p;
}
int
main ()
{
int i = *foo ();
if (i != i0)
abort ();
return 0;
}
only the last item of 8.5.3 Paragraph 5 that applies to the return
value of foo, and hence foo is translated as if it was written as:
const int *const &
foo ()
{
int const *const p0 = p;
return p0;
}
I.e. the reference is bound to a temporary that lives only lives till
foo exits (in accordance with 12.2 [class.temporary] Paragraph 5).
Thus, using the value of *foo () invokes undefined behaviour.
The programmer will more likely expect foo to behave like it was written:
const int *const &
foo ()
{
const int *const *p0 = &p;
return *p0;
}
This works because the last item of 8.5.3 paragraph 14 applies, i.e.
standard conversions apply. We can't convert to the cv-unqualified version
of the destination type, but that is not necessary since we can convert to
the cv-qualified destination type according to 4.4 [conv.qual] paragraph 4.
I think similar language to 4.4 paragraph 4 should be added to the
definition of reference compatibility in 8.5.3.
This could possibly combined with array type declarators as alternatives to
'pointer to' to also address DR 450.
--
Summary: reference-compatible is defined too narrowly in
[decl.int.ref]
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: amylaar at gcc dot gnu dot org
OtherBugsDependingO 29842
nThis:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29859
