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From: rmtodd@uokmax.UUCP (Richard Michael Todd)
Newsgroups: comp.os.minix
Subject: Global variables (was Re: More on sh/shar
Message-ID: <587@uokmax.UUCP>
Date: Thu, 4-Jun-87 23:34:45 EDT
Article-I.D.: uokmax.587
Posted: Thu Jun  4 23:34:45 1987
Date-Received: Tue, 9-Jun-87 04:29:13 EDT
References: <1643@encore.UUCP> <581@uokmax.UUCP> <498@sortac.UUCP>
Organization: University of Oklahoma, Norman, OK
Lines: 60
Summary: Clarification of previous posting

In article <498@sortac.UUCP>, fdg@sortac.UUCP (Fred Gant) writes:
> In article <581@uokmax.UUCP> rmtodd@uokmax.UUCP (Richard Michael Todd) writes:
> >In article <1643@encore.UUCP>, paradis@encore.UUCP (Jim Paradis) writes:
> >file foo.c:
> >	int a;
> >...
> >
> >file bar.c:
> >	int a;
> >...

> daily and can comment on that.  In your example, "int a" is not global in
> either case.  It is in fact local to the file that declares it.  To be
> global, it must be declared in a header file, such as sh.h, or be declared
> outside of the function.  An example would be
 I guess I wasn't clear enough in my original statement.  I meant that the
two "int a" definitions were in two separate files, each one being a global
definition (i.e. outside any function).  Here's a full example of the kind
of code I was referring to:
------------------ File #1: foo.c --------------------
int a;
main() {
	a = 5;
	printf("%d\n",a);
	bar();
	printf("%d\n",a);
}
---------------- File #2: bar.c ----------------------
int a;
bar() {
	a = 7;
}
---------------- end --------------
In this example, the 'a's in both files are global variables.  On UNIX
systems, compiling with "cc foo.c bar.c" will succeed and in the resulting
program both modules, when referring to 'a' refer to the same memory
location, thus the program will print out:
5
7
On non-UNIX systems, the linker will complain about multiple definitions
of the symbol a.
Note that the functions 'main' and 'bar' above do not have to declare
within the function body that 'a' is extern, as you did in your example
code:
> int a, b;  /* These are global. */
> main()
> {
> 	extern int a, b;   /* a & b are globals used by main */
> 	int c, x;          /* c, x, & y are local to main    */
It's probably a good practice to do so, since it warns the reader that
the function uses these global variables, but I know of no compiler
that requires the extern as long as the function appears in the source
file after the definition of the variables.  
> This posting is not meant to be critical.  I am attempting to clear up a
> point of confusion.
Ditto.
___________________________________________________________________________
Richard Todd
USSnail:820 Annie Court,Norman OK 73069
UUCP: {allegra!cbosgd|ihnp4}!okstate!uokmax!rmtodd