From: j DOT aldrich6 AT genie DOT com
Message-Id: <199605122216.AA124429376@relay1.geis.com>
Date: Sun, 12 May 96 22:13:00 UTC 0000
To: djgpp AT delorie DOT com
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset=us-ascii
Subject: Re: more sizeof questions

Reply to message 2215819    from ELIZ AT IS DOT ELTA. on 05/12/96  4:32AM


>> 2)  Conditionally pack the structure only if you are using a GNU compiler,
>
>Most 32-bit compilers pad structs to avoid significant runtime penalty
>for unaligned accesses.  So, conditioning that code on GCC alone is not
>exactly the correct procedure.  You should use some symbol that implies a
>32-bit compiler.

Actually, I was wondering about that... is there a specific define I can
check to find out if a given compiler pads structs, or would I have to
test for each individual compiler?  Also, according to the docs,
__attribute__ only works with later versions of gcc; is there any way
besides #pragma pack() to pack structs on other compilers?

>There are many headers in any Unix program that cannot be found on any
>other DOS compiler except DJGPP; unistd.h is only one of them.  This is
>one of the main problems that make porting a Unix programs to the other
>compilers a programmer's nightmare.

And one of the main reasons I like DJGPP so much.  :)

BTW, I noticed something slightly odd a while back about #defines.  I
ran gcc with options to output a list of all macro definitions (-dM, I think),
and discovered that apparently, DJGPP defines by default both
"MSDOS" and "unix".  Isn't this a bit contradictory?

John