Re: [Tinycc-devel] global variables in tcc

[Lluís Batlle i Rossell]

On Mon, Apr 01, 2013 at 08:58:06PM +0200, Daniel Glöckner wrote:
> Hi,
> 
> On Mon, Apr 01, 2013 at 04:55:18PM +0200, Lluís Batlle i Rossell wrote:
> > > GCC and Clang allow these to be merged together at link-time, which
> > > means users who make mistakes such as missing `extern' in header files
> > > still get the multiple definitions merged.
> > > 
> > > tcc is stricter and perhaps more conformant in disallowing this.
> > 
> > I think that the C standard requires the gcc and clang behaviour, 'extern'
> > never being a required word.
> > 
> > No?
> 
> I just took a look inside the N1570 C11 draft.
> Chapter 6.9 paragraph 5 says:
> 
> "If an identifier declared with external linkage is used in an expression
> ([...]), somewhere in the entire program there shall be exactly one external
> definition for the identifier; otherwise, there shall be no more than one."

>From K&R:

"An external declaration for an object is a definition if it has an initializer.
An external object declaration that does not have an initializer, and does not
contain the extern specifier, is a tentative definition. If a definition for an
object appears in a translation unit, any tentative definitions are treated
merely as redundant declarations. If no definition for the object appears in the
translation unit, all its tentative definitions become a single definition with
initializer 0."

I don't know if this is a fight between K&R and the C11 draft. :)

Regards,
Lluís.