question about scope & linkage

[Conor P. Cahill]

In article <14270 at haddock.ima.isc.com>, karl at haddock.ima.isc.com (Karl Heuer) writes:
> In article <1001 at virtech.UUCP> cpcahil at virtech.UUCP (Conor P. Cahill) writes:
> >[Stuff about real vs. tentative definitions]  A global symbol may have
> >unlimited tentative definitions, but only 1 real definition.
> 
> I think you're confusing tentative definitions with non-defining declarations.

I am not.

> 
> >In other words, you can have "int i;" in every .c and they will all refer to
> >the same data space.
> 
> This is not correct.  A tentative definition retroactively becomes a real
> definition if the end of the source file is reached without seeing a real
> definition.  The purpose of the tentative-definition nonsense is not to force
> the Common-block storage model to work; it's to allow forward reference to
> non-global identifiers.
> 

A tentative definition of a data object is not resolved at the end of source
module,  but at link time.  I quote from K&R2 pg 227,

	...In the alternate formulation, which is usual in UNIX systems and
	recognized as a common extension by the Standard, all tentative 
	definitions for an externally linked object, throughout ALL the
	translation units of a program are cosidered together instead of
	in each translation unit separately.  If a definition occurs somewhere
	in the program, then the tentative definitions become merely 
	declarations, but if no definition appears, then all its tentative
	definitions become a definition with initializer 0.


"tentative definition" is defined as "an external object declaration that
does not have an initializer, and does not contain the extern specifier"

Therefore what I said is absolutely correct.  BTW, I don't see how any of
this applies to a "forward reference to non-global identifiers".