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From: blarson@dianne.usc.edu (bob larson)
Newsgroups: comp.std.c
Subject: Re: Structure Member Padding
Message-ID: <25874@usc.edu>
Date: 14 Jul 90 06:15:59 GMT
References: <13321@smoke.BRL.MIL> <10420@ogicse.ogc.edu> <1990Jul13.104407.29078@jarvis.csri.toronto.edu>
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In article <1990Jul13.104407.29078@jarvis.csri.toronto.edu> flaps@dgp.toronto.edu (Alan J Rosenthal) writes:
>For:
>	struct { int i; char c; } var;
>and
>	struct { int i; char c[1]; } var;
>to have different layouts, indeed different semantics with respect to layout,
>would be quite bizarre.

Prime's C compiler stores char variables in the right half of a 2-byte
"halfword", and character arrays are packed and start at the left.
This does break code that makes assumptions about unions or that no
padding is between individually declared chars in a structure.
As far as I know, they havn't changed this behavor in their beta-test
ansi compiler.

union {
    struct { char a, b, c, d;} x;
    char y[4];
}

Code that assumes that x.a is the same as y[0] and x.d is y[3] will not
work on prime's c compiler.  note that &a+1 != &b
Bob Larson (blars)	blarson@usc.edu			usc!blarson
	Hiding differences does not make them go away.  Accepting
	differences makes them unimportant.
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