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From: lav@mtsbb.UUCP (L.A.VALLONE)
Newsgroups: net.unix,net.micro.att,net.lang.c
Subject: query: argument passing on UNIX PC, VAX, et al
Message-ID: <168@mtsbb.UUCP>
Date: Thu, 15-May-86 20:12:38 EDT
Article-I.D.: mtsbb.168
Posted: Thu May 15 20:12:38 1986
Date-Received: Sat, 17-May-86 04:07:21 EDT
Distribution: na
Organization: AT&T-Information Systems, Middletown, NJ
Lines: 41
Xref: watmath net.unix:7875 net.micro.att:1188 net.lang.c:9042

I am interested in the precision used by various C compilers when
passing arguments on the stack to a called routine.  For example:

    some_routine_or_main()
    {
	char	a,b;

	foo(a,b)
    }

    foo (a,b)
    long a,b;

    {
	printf("%#lx\t%#lx\n", a, b);
    }

I tried a program similar to the above on a vax and a UNIX PC
and in both cases the values of 'a' and 'b' were correctly
passed.  Given that a long on both machines is 32 bits and a char
is 8 bits, from this I assumed that both compilers are expanding
'a' and 'b' to 32 bits before putting them on the stack.  I might
have expected this for the vax, but not for the UNIX PC (68000
based).

I also tried seperating the functions among 2 files to eliminate
the possibility of the compiler detecting the inconsistency and
correcting (though this doesn't mean the loader isn't being
smart).  Again, it worked.

Does anyone know if my assumption is correct?  Is my model
not telling me what I think it is?  Are there any C compilers that
don't behave this way?

Please respond by Email and I'll post if anyone else is interested.

			Thanks in advance
-- 

Lee Vallone		AT&T Information Systems	Merlin
{... ihnp4, mtuxo}!mtsbb!lav