Hi Ho!
On Thu, 2009-04-30 at 11:57 -0700, Ian Lance Taylor wrote:
> What you are describing is a common and traditional implementation of C,
> but it is not strictly standard conformant. The ISO C standard says
> that "int i;" is always a definition, and "extern int i;" is always a
> declaration. What you decribe is listed as a common extension (at least
> in C90--I didn't bother to check C99).
Thank you for clarifying further in light of the standard.
> Yes. In a function (not variable) declaration, the "extern" is
> optional. This is true in both C and C++.
Thanks for the answer. I had been pondering upon this point for about a
year or so since I hacked the Linux kernel for the very last time. It is
because in some header files, some prototypes use "extern" and some
don't. So, I was curious as to whether they have a different semantic.
> > Also, is there any difference in defining a non-inline function with
> and
> > without "extern" in C? That is, is there any difference between:
> >
> > extern int foo (int *bar)
> > {
> > return *bar + 5;
> > }
> >
> > and
> >
> > int foo (int *bar)
> > {
> > return *bar + 5;
> > }
> >
> > ?
> >
> > I think they are also identical. Am I right? Who knows the one with
> > "extern" can be overridden in another TU defining its own definition
> > without "extern".
>
> These are not identical, but the meaning in C is complex because it
> changes depending on which standard you are using. Look at the docs
> for
> the -fgnu89-inline option and the gnu_inline function attribute.
Ah, I get it.
Yes, I am aware of the different semantic when inline is involved like
what you have specified here:
http://gcc.gnu.org/ml/gcc/2006-11/msg00006.html
> Ian
Thanks for your answers :-)
--
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Eus (FSF member #4445)
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