Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work

On May 5, 2012, at 2:56 PM, Leon Timmermans wrote:

> On Sat, May 5, 2012 at 6:25 PM, Craig A. Berry <craigberry@mac.com> wrote:
>> Thanks for the suggestion.  That might work, but might also fall afoul of the naked semicolon problem noted in the comment in perl.h:
>> 
>> #define NOOP /*EMPTY*/(void)0
>> /* cea2e8a9dd23747f accidentally lost the comment originally from the first
>>   check in of thread.h, explaining why we need dNOOP at all:  */
>> /* Rats: if dTHR is just blank then the subsequent ";" throws an error */
>> /* Declaring a *function*, instead of a variable, ensures that we don't rely
>>   on being able to suppress "unused" warnings.  */
>> #define dNOOP extern int Perl___notused(void)
>> 
>> But maybe that error would only happen with C and not C++?
> 
> That's what he just said, it's only a problem when mixed statements
> and declarations are not allowed. They are allowed in C99 and C++, but
> not in C89.
> 
>> The definition of dNOOP is an extremely well-trodden line of code with lots of changes demonstrating that anything that fixes a problem with it is highly likely to introduce one or more other problems.
>> 
>> I don't actually understand why we need a dNOOP that's distinct from NOOP, i.e., why we can't just do:
> 
> because:
> 
> dNOOP;
> int foo;
> 
> Should work on a strict C89 compiler. That means that on such a
> compiler, dNOOP must translate to a declaration. On a more lenient
> compiler it doesn't matter what it compiles to (as long as it is a
> no-op, obviously).

Thanks, Leon.  Since I spend much of my time these days in vbscript and other perversions I do in fact need to be clobbered over the head with C basics sometimes, as you suspected.  I simply hadn't remembered that a semicolon by itself was a statement, but I now see that C99 says, in section 6.8.3, "A null statement (consisting of just a semicolon) performs no operations."

So Tony's suggestion should be fine, and we'll have plenty of time to smoke it thoroughly in 5.17.

________________________________________
Craig A. Berry
mailto:craigberry@mac.com

"... getting out of a sonnet is much more
 difficult than getting in."
                 Brad Leithauser

• C++, XS, and dNOOP, or Doing Nothing is Hard Work by Craig A. Berry
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Tony Cook
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Craig A. Berry
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Leon Timmermans
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Craig A. Berry
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Craig A. Berry
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Mark Berryman
• Re: C++, XS, and dNOOP, or Doing Nothing is Hard Work by Craig A. Berry