On 06/27/2010 08:14 PM, Harald van Dijk wrote:
On Sun, Jun 27, 2010 at 05:46:28PM +0300, Nikos Chantziaras wrote:
On 06/27/2010 03:23 PM, Harald van Dijk wrote:
The compiler is not totally free to ignore the register keyword.
Both the C and the C++ standards require that the compiler complain
when taking the address of a register variable. Other compilers will
issue a hard error for it. Fixing the code to not declare the
variable as register would be the correct thing to do.
No, it would not be the correct thing to do, because of the following.
(This is part of a discussion between me and someone quite smarter than
me, who explained the issue in detail.)
[snip]
That explanation seems to be written by someone who does not know that
taking the address of a register variable is simply not allowed.
It is allowed. Section 7.1.1, Paragraphs 2 and 3 of the C++ standard:
The register specifier [...] specifies that the named variable has
automatic storage duration (3.7.3). A variable declared without a
storage-class-specifier at block scope or declared as a function
parameter has automatic storage duration by default.
A register specifier is a hint to the implementation that the variable
so declared will be heavily used. [ Note: the hint can be ignored and in
most implementations it will be ignored if the address of the variable
is taken. This use is deprecated (see D.4). — end note ]
OK, long read, but the the conclusion is that "fixing the code to not
declare the variable as register would be the correct thing to do" it
*not* the correct thing to do. The correct thing to do is to ignore the
warning, which is not possible if warnings are turned into errors.
And which is not possible if the warning is a hard error in the first place.
You also mentioned that "other compilers will issue a hard error for
it." That sounds rather strange, and I wonder which compilers that
might be; someone should file a bug report against them ;)
Well, let's start with gcc; that's quite an important one for Gentoo...
That code compiles just fine. I don't know of any GCC version that
issues an error for this rather than just a warning.
