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From: terra AT diku DOT dk (Morten Welinder)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Structure sizing problem
Date: 7 Jan 1996 14:35:36 GMT
Organization: Department of Computer Science, U of Copenhagen
Lines: 29
Sender: terra AT tyr DOT diku DOT dk
Message-ID: <4colno$dc0@odin.diku.dk>
References: <4cofrl$7d3 AT news DOT mdata DOT fi>
NNTP-Posting-Host: odin.diku.dk
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

@megabaud.fi writes:

>struct main_directory_entry {
>       char name[7];
>       unsigned long offset;
>       unsigned long size;
>};

>Borland C++ returns sizeof(main_directory_entry)=15 and
>djgpp returns 16, which causes little problems with
>file-reading routines...

>However when I tested sizeof(main_directory_entry.name) it returned
>7 and unsigned longs returned 4. 7+4+4=15 isn't it?

Certainly, but 7+1+4+4 is 16.  gcc aligns longs for faster access.


>Have I missed some piece of information or is this a bug in compiler?

The memory layout is implementation dependent.  You can get the
packed behaviour by adding the "packed" attribute.  See the
source file src/debug/fsdb/fullscr.c for an example of how to
do it.

Morten


PS: fix your email return address.