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From: rbbb@rice.EDU (David Chase)
Newsgroups: net.lang.c
Subject: Structure alignment question
Message-ID: <3550@brl-smoke.ARPA>
Date: Thu, 4-Sep-86 14:07:55 EDT
Article-I.D.: brl-smok.3550
Posted: Thu Sep  4 14:07:55 1986
Date-Received: Fri, 5-Sep-86 06:47:33 EDT
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Suppose I have a structure "foo" and function returning a "struct foo".

    struct foo {
	int a,b;
	};
    struct foo bar() {
	struct foo baz;
	...
	return baz;
	};

Note that the structure contains two ints.  I will assume that an "int" is
the same size as some machine quantity called a "word", and that
word alignment is desirable.  I assume therefore that all instances of the
structure generated by the compiler will be word-aligned.

C compilers that I have seen supporting structure-valued functions pass a
hidden parameter to the function containing the address to store the
result.

Can a compiler assume that the storage for the result is word-aligned?
(That is, can a compiler make the same assumptions when returning a
structure that it does when assigning a structure?)
If so, why?  If not, why not?

David