Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!husc6!bunny!rhb6
From: rhb6@bunny.UUCP (Robert H. Barkan)
Newsgroups: comp.sys.ibm.pc
Subject: MSC multiple-definition bug or feature?
Keywords: Strange MSC linker behavior
Message-ID: <6215@bunny.UUCP>
Date: 19 Oct 88 23:41:31 GMT
Organization: GTE Laboratories, Waltham, MA
Lines: 59


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:

file x1.c:                               file y1.c:
==========                               ==========
int x, eks = 'x';                        int x, why = 'y';

main()                                   y()
{                                        {
    x = eks;                                 x = why;
    printf("File X1, x: %c\n", x);           printf("File Y1, x: %c\n", x);
    y();                                 }
    printf("File X1, x: %c\n", x);                
}                                

So far, so good.  Now change x to something other than an integer,
recompile, and try to link together x2.obj and y2.obj:

file x2.c:                               file y2.c:
==========                               ==========
int *x, eks = 'x';                       int *x, why = 'y';

main()                                   y()
{                                        {
    x = &eks;                                x = &why;
    printf("File X2, *x: %c\n", *x);         printf("File Y2, *x: %c\n", *x);
    y();                                 }
    printf("File X2, *x: %c\n", *x);
}

Surprise, it's no longer an error!  The linker is happy now, and produces
x.exe.  And of course running x.exe gives the (un)expected side effect:
    File X2, *x: x
    File Y2, *x: y
    File X2, *x: y
Now, just for fun, try linking x2.obj with y1.obj.  Now we have x
defined as (int *) in x2, and x defined as (int) in y1.  The linker is
still happy, and the side effect is even better:
    File X2, *x: x
    File Y1, x: y
    File X2, *x: [ some smiley faces, musical notes, & other ascii "noise" ]

Finally, I took this code over to a Sun3/OS3.5, and it didn't complain
about any of the versions!  Of course, you normally wouldn't code like
this (these examples were simplified from a bug we found in a larger
program).  But what is unique to the MS linker about multiple definitions
of int, but not other types?


Bob Barkan                          rhb6%bunny@harvard.harvard.edu
GTE Labs                            rhb6@gte.com
40 Sylvan Road
Waltham, MA  02254

-- 
Bob Barkan				GTE Laboratories
					40 Sylvan Rd
rhb6%bunny@harvard.harvard.edu		Waltham, MA 02254
rhb6%gte.com@relay.cs.net		(617) 466-2568