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From: jwp@uwmacc.UUCP (Jeffrey W Percival)
Newsgroups: net.unix-wizards
Subject: ULTRIX linker bug???
Message-ID: <336@uwmacc.UUCP>
Date: Wed, 8-Oct-86 21:36:26 EDT
Article-I.D.: uwmacc.336
Posted: Wed Oct  8 21:36:26 1986
Date-Received: Thu, 9-Oct-86 03:47:24 EDT
Distribution: net
Organization: UWisconsin-Madison Academic Comp Center
Lines: 35

I tracked down a bug in a big program I have, but was
a little surprised with what I learned.  My program looked like this:

float x;
float y;
main()
{
...
}

Now, in /usr/lib/liblocal.a, there is a subroutine whose source file
looks like this:

double x;
double y;
sub()
{
	y = 10.0;
	print y
	x = expression;
	print y
}

I linked it with "cc main.o -llocal -o main"

Much to my surprise, the value of y was changed from 10.0 to 0.0
as a result of the assignment to x.  I thought (perhaps mistakenly)
that the scope of a variable declared at the beginning of a file
extended only throughout that file.  Even if that is not true,
shouldn't I have gotten a "multiply declared" message?

I tried bringing sub.o into my directory and typing "cc main.o sub.o"
and got the expected "multiply declared" complaint.
-- 
	Jeff Percival ...!uwvax!uwmacc!sal70!jwp or ...!uwmacc!jwp