MSC multiple-definition bug or feature?

[Brandon S. Allbery]

As quoted from <1099 at dutinfd.UUCP> by oosten at dutinfd.UUCP (Gertjan van Oosten):
+---------------
| In article <6215 at bunny.UUCP>, rhb6 at bunny.UUCP (Robert H. Barkan) writes:
| > In MSC 5.x, compile the following 2 files, then link x1.obj and y1.obj.
| > The linker should complain because "int x" is multiply defined:
| 
| In one C file, I had the following (external) declaration: 
| static int x; 
| 
| In another C file, I had: 
| extern int x; 
| 
| Compilation and linkage produced no "Unresolved external" message!!!!! 
| How nice of Microsoft.... 
| 
| I also tried this on four other machines. Here come the results, fasten 
| seatbelts and refrain from smoking: 
| A 3B1 running System V version 3.5: 
|       No linker error message; however, lint complains about "Used but not 
|       defined". 
| A Microdutch running System V Release 2 X/OPEN: 
|       No linker error message; however, lint complains about "Used but not 
|       defined". 
| A VAX running 4.3 BSD: 
|       Linker produces error message; lint complains. 
| A PDP-11/73 running ULTRIX-11: 
|       !!!Linker produces error message; lint DOESN'T complain!!! 
| 
| So only 4.3 BSD functions correctly; that's ONE out of FIVE!!! 
| Enough said... 
+---------------

But did you try to run it and see which "x" was in use?

In K&R C, the default storage class of a variable declared outside a function
is "extern".  The corollary is that the "extern" declaration serves both as
reference and as linker definition, i.e. the "extern int x" is a different
variable from the "static int x".  If they have the same address, however,
the linker is broken.  Note also that K&R C isn't followed all that closely
by many compilers in this respect; they instead have the default storage
class as a sort of "invisible" storage class which acts as reference and
definition, while "extern" is merely reference.

++Brandon
-- 
Brandon S. Allbery, comp.sources.misc moderator and one admin of ncoast PA UN*X
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