* David Brown: >> C23 changes meaning of of extern foo(); to match the C++ >> interpretation of extern foo(void);. I don't think we should warn >> about that. If we warn, it would be at the call site. > > I'm not sure I fully agree. "extern foo();" became invalid when > implicit int was removed in C99. But "extern T foo();", where "T" is > void or any type, has changed meaning between C17 (and before) and > C23.
My concern is that the warning would not really be actionable. Encouraging programmers to change foo() to foo(void) in declarations seems merely busywork. C++ doesn't need this, and future C won't need it, either. > IMHO I think calling "foo" with parameters should definitely be a > warning, enabled by default, for at least -std=c99 onwards - it is > almost certainly a mistake. (Those few people that use it as a > feature can ignore or disable the warning.) It's possible to disable this warning in C23 by declaring foo as ”extern T foo(...);”. Not sure if this has ABI implications. > I would also put warnings on the declaration itself at -Wall, or at > least -Wextra (i.e., "-Wstrict-prototypes"). I think that things that > change between standards, even subtly, should be highlighted. > Remember, this concerns a syntax that was marked obsolescent some 35 > years ago, because the alternative (prototypes) was considered > "superior to the old style on every count". I still think the declaration is quite harmless if we warn at call sites. Thanks, Florian
