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From: pekka@paix.ikp.liu.se (Pekka Akselin [The Mad Midnight Hacker])
Newsgroups: comp.lang.c
Subject: Re: Structure padding
Message-ID: <124@paix.ikp.liu.se>
Date: 11 Apr 89 09:52:16 GMT
References: <440@front.se> <8392@xanth.cs.odu.edu>
Organization: PA Mikroresurs, Linkoping, Sweden
Lines: 50

In article <8392@xanth.cs.odu.edu> kremer@cs.odu.edu (Lloyd Kremer) writes:
>In article <440@front.se> zap@front.se (Svante Lindahl) writes:
>>Consider a struct consisting of a few character arrays, for example:
>>
>>	stuct foo {
>>	    char bar[3];
>>	    char baz[6];
>>	    char frotz[4];
>>	} fred;
>>
>>I need to know if I can safely assume that there will not be any
>>padding between the arrays.
[...]
>You would simply define one big array (a C array is guaranteed to be
>contiguous), and do the internal indexing yourself.  There should be no
>performance degradation since the compiler would arrange for such indexing
>anyway.  Also, some well-chosen macros could make using the strings easier.
[...]

How about this???

union {
	struct foo {
	    char	Bar[3];
	    char	Baz[6];
	    char	Frotz[4];
	} fred;
	char	SomeString[3 + 6 + 4];
} Strings;

#define bar	Strings.Bar
#define baz	Strings.Baz
#define	frotz	Strings.Frotz

Would there be padding between the Bar, Baz and Frotz arrays in this case?

My compiler generates the following line for the union above;

      .comm   _Strings,13

and the same for structure fred;

      .comm   _fred,13

Have a nice day!
-- 
Pekka					[The Mad Midnight Hacker Strikes Again]
_______________________________________________________________________________
pekka@paix.ikp.liu.se			...!uunet!enea!liuida!prodix!paix!pekka
Pekka Akselin, PA Mikroresurs, Sweden  (The Land Of The Mad Midnight Hacker 8-)