From: "DeHackEd" <notgiven AT out DOT com>
Newsgroups: comp.os.msdos.djgpp
References: <369A62B1 DOT 5D936926 AT regiolicht DOT nl>
Subject: Re: Char-in-struct bug!?
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Message-ID: <8Ctm2.3743$id.207@cabot.ops.attcanada.net>
Date: Mon, 11 Jan 1999 15:56:15 -0500
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

>I found out, that when you use a struct with djgpp (both in .c and .cpp
>files) like this:
>
>typedef struct {
>    char x, y, z;
>  } my_type1;
>
>the size will be 3 bytes, but when you have one like this:

Yes, it is about alignment. That's normal. If you want to correct this, read
on...

>
>typedef struct {
>    char x, y, z;
>    int i;
>  } my_type2;
>
>the size will be 8 bytes, even if I remove y or y and z. When I add a
>char behind i, the size will grow to 12 bytes! When using short ints, I
>get the same problem.
>
>Is this some kind of dword/long int aligning? Or is it a bug?

It is for alignment. The CPU can access data better if it's aligned on a
specific size. Int's should be aligned on a 4 byte boundry, chars are fine the
way they are. FAQ section 22.10


>
>I found this strange thing when I made a structure containing a .bmp
>header, which uses as the first two bytes, the chars 'B' and 'M'.
>Compiling with turbo c++ 3.0 gives a (correct) structure size of 54, but
>compiling with djgpp gives a size of 56 (2 zero chars are added after
>the first two).
>
>If this is not a bug, how can I correct this?
>
>Henno Vermeulen.
>
>