Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!motcid!kreidler
From: kreidler@cell.mot.COM (Joe Kreidler)
Newsgroups: comp.lang.c
Subject: Memory allocation of structures
Message-ID: <1457@navy8.UUCP>
Date: 5 Mar 90 15:06:40 GMT
Distribution: usa
Organization: Motorola Inc. - Cellular Infrastructure Div., Arlington Heights, IL 60004
Lines: 39

For the 64000, structures are word aligned. What I didn't
realize is that the end of the structure is also word aligned.
Let me explain what I mean by the previous sentence with an example.

Given the following declaration:

     struct {
             short a;
             short b;
             short c;
     } foo;
     short x;

For the compiler I'm using, "short" is an 8-bit integer. "foo" is
word aligned and uses three bytes. However, "x" is also word aligned.
Since "x" follows a structure it starts on a new word boundary.

This doesn't make sense to me. If the above declaration was changed to

     short a;
     short b;
     short c;
     short x;

then "x" would use the byte directly following "c". I was expecting the
first declaration to be allocated the same way.

Is there some reason for structures being allocated memory as I described
above? Is this observation part of the ANSI standard? Any insights are
appreciated.

Thanks in advance,
Joe

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Joe Kreidler, Motorola C.I.D     1501 W Shure Drive
...!uunet!motcid!kreidler        Arlington Heights, IL 60004
                                 708-632-4664
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