Paul Mensonides writes:
-----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Dave Steffen
Yes, I've seen this in the GCC documentation. Unfortunately, it doesn't help if you're doing the sort of preprocessor metaprogramming we're doing. In one case in particular, the end result of the macro really is supposed to be a _function declaration_, not a section of code.
In another case, it shows up from the construct
#define NUM_SIG_CONNECTION_FUNCTIONS_FOR_MEMBERS(first,last) \ BOOST_PP_REPEAT_FROM_TO(BOOST_PP_ADD(first,1),BOOST_PP_ADD(last,2),\ NUM_SIG_DECLARE_CONNECT,BOOST_PP_EMPTY)
I don't claim to understand everything that's going on here (even remotely), but GCC 3.2 and 3.3 are very happy with the usage (in a header file)
NUM_SIG_CONNECTION_FUNCTIONS_FOR_MEMBERS(0, MAX_SIGNAL_ARGS);
while 3.4 complains about that semicolon. What I'm asking is A) does anyone know if 3.4 has a particular -Wno-extra-semicolon, or equivalent, to turn off that warning; or B) what is the proper preprocessor metaprogramming technique to silence the warning.
The proper technique is to get rid of the semicolon. A macro invocation is not an expression, though it may expand to one, and it is not a function call. Adding the semicolon and then trying to get around the warning (which should be an error) only encourages the view that macros invocations and function calls are equivalent. Nearly all macro-related problems (other than name collision) are a result of this fundamentally flawed perspective. The use of all caps should be make it obvious that a macro is involved. Making macro invocations appear more like function calls is evil--don't do it.
Right. These macros are _not_ trying to look like function calls. Trying to make macros act like function calls _is_ evil, and we don't do that. Much. :-) This is not the problem. These macros _are_ part of some metaprogramming constructs that are attempting to automate the declaration of a suite of fuctions; or, alterately, are the NUM_SIG_CONNECTION_FUNCTIONS_FOR_MEMBERS thing I mentioned above, which is part of our wrapper around Boost's signal library. I claim that our macros and use thereof is A) correct and B) safe. It just so happens that these macro constructs occasionally expand to something that has an extra semicolon, which triggers a warning in GCC 3.4 that we haven't seen before. What I'm asking is this: assuming that our macros and useage thereof is correct, how do we A) silence the GCC warning about extra semicolons, or B) modify the construct so that the trailing semicolon is "legal", or at least "something that won't scare the compiler". :-) ---------------------------------------------------------------------- Dave Steffen, Ph.D. "There are two ways to write error-free Software Engineer IV programs; only the third one works." Numerica Corporation ph (970) 419-8343 x27 "Pie are not square. Pie are round. fax (970) 223-6797 Cornbread are square" dgsteffen@numerica.us ... anon (usenet) ___________________ Numerica Disclaimer: This message and any attachments are intended only for the individual or entity to which the message is addressed. It is proprietary and may contain privileged information. If you are neither the intended recipient nor the agent responsible for delivering the message to the intended recipient, you are hereby notified that any review, retransmission, dissemination, or taking of any action in reliance upon, the information in this communication is strictly prohibited, and may be unlawful. If you feel you have received this communication in error, please notify us immediately by returning this Email to the sender and deleting it from your computer.