Path: utzoo!attcan!uunet!mcvax!ukc!reading!cf-cm!cybaswan!iiit-sh
From: iiit-sh@cybaswan.UUCP (Steve Hosgood)
Newsgroups: comp.sys.ibm.pc
Subject: MSC v4.0 Bug??.
Summary: Global variable declarations broken?
Keywords: declaration, C, extern
Message-ID: <65@cybaswan.UUCP>
Date: 31 Aug 88 14:23:54 GMT
Reply-To: iiit-sh@cybaswan.UUCP (Steve Hosgood)
Organization: Institute for Industrial Information Technology
Lines: 48
References:

I've got some routines in a library which make use of some references to
global data. In a different file (also in the library) are all the declarations
of this data. Here's an example:

File 'fred.c' (yields object module 'fred'):

	extern int xxx;
	
	fred()
	{
	........
	xxx = 1;
	.......
	}

Data declaration file 'declare.c' (yields object module 'declare'):

	int xxx;
	....
	....

After compilation (with MSC 4.0) the object files are linked (with MS Lib 3.04).
The library is then used to resolve a call to routine 'fred'.

Well, according to K&R, this *ought* to work. Object module 'fred' refers
to the data (but doesn't declare it) using the extern statement. Object module
'declare' declares the variable 'xxx'. All should be happy. All UN*X systems
I've seen have been happy with this.

Not here! For this to work, the statements declaring the data in 'declare.c'
actually have to *initialise* each declaration, otherwise they're not seen in
the library. If I initialise all the variables explicitly to zero, all is well.

I eventually discovered that this 'feature' is documented in an obscure way
in the manual, though it took me over an hour to find it. This seems to be
a fault to do with the library system, or the linker, as programs compile OK
without having to initialise data when libraries arn't involved. Any comments?

Thanks in advance,

-----------------------------------------------+------------------------------
Steve Hosgood BSc,                             | Phone (+44) 792 295213
Image Processing and Systems Engineer,         | Fax (+44) 792 295532
Institute for Industrial Information Techology,| Telex 48149
Innovation Centre, University of Wales, +------+ JANET: iiit-sh@uk.ac.swan.pyr
Swansea SA2 8PP                         | UUCP: ..!ukc!cybaswan.UUCP!iiit-sh
----------------------------------------+-------------------------------------
            My views are not necessarily those of my employers!