[cfe-dev] Error when testing clang with VC++ RTL and Boost MPL

[Karen Shaeffer]

On Wed, Nov 13, 2013 at 04:29:27PM -0700, Richard wrote:
> 
> In article <l610fi$4sj$3 at ger.gmane.org>,
>     Edward Diener <eldlistmailingz at tropicsoft.com> writes:
> 
> > Is not -1 in the range of an 'int' ?
> 
> Yes, but you didn't write -1 in your source file.
> 
> > Is not 0xffffffff equivalent to -1 
> > as a signed value ?
> 
> No.  They are two different integer literals.
> 
> > What am I missing here ?
> 
> Read the mentioned section of the standard carefully.  I've read this
> part and it isn't particularly confusing or difficult.


Hello,
My interpretation of this is that 2.14.2 defines how the compiler interprets the
literal. That isn't the problem though. The problem arises, when you attempt to
implicitly convert the compiler's interpretation to a signed integer. And the
error is narrowing. clang emits this error:

hexLiteralsUnsigned.cpp:16:24: error: constant expression evaluates to 4294967295 which cannot be
      narrowed to type 'int' [-Wc++11-narrowing]
    signed int isigned{0xFFFFFFFF};

You can avoid this error by simply using a cast:
signed int isigned{static_cast<signed int>(0xFFFFFFFF)};

FYI, g++-4.8.1 only emits a warning about the narrowing, then successfully completes the
compilation. Based on the standard section 8.5.4, I believe clang is correct to emit the
error. And 5.17.9 declares an assignment, such as 'int i = {0XFFFFFFFF};' to be a narrowing
error as well. I believe clang is correct to emit a narrowing error.

enjoy,
Karen
-- 
Karen Shaeffer                 Be aware: If you see an obstacle in your path,
Neuralscape Services           that obstacle is your path.        Zen proverb