GCC/EDG Extension: Comparison of void** and void const** rejected.

[llvmbot]

Bugzilla Link	6346
Resolution	FIXED
Resolved on	Feb 25, 2010 16:30
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor

Extended Description

g++ accepts the code fragment: int main(void) { void** i; void const** j; i == j; }

clang++ rejects this, with the error:

t.cc:1:46: error: comparison of distinct pointer types ('void ' and
'void const ')
int main(void) { void i; void const j; i == j; }
~ ^ ~

[DougGregor]

I'm looking into this one...

[DougGregor]

This code is ill-formed, because the composite pointer type (as defined in [expr.rel]p2 would be

void const **

However, there's no standard conversion from void ** to const void ** (see [conv.qual]p4).

However^2, both GCC and EDG accept this code, and it's a completely reasonable to allow this comparison. The question is how, because we either:

• Allow the conversion despite the fact that it's not a proper qualification conversion
• Change the formulation of "composite pointer type" to produce, e.g., void const * const *, which both can convert to.

I favor the latter, but we shouldn't make this change without also bringing the issue to the C++ committee for consideration.

[DougGregor]

Fixed in r97177.