What you can do too, instead of setting alignment for the project, is insert
a pragma like the following
#pragma options align = powerc
typedef struct
{
}
#pragma options align = mac68k
not absolutely sure about these pragmas but you'll find them in the doc
--
Eric Vergnaud
President of Street Soft
----------
>De�: "Greg Bungo" <[EMAIL PROTECTED]>
>� : <[EMAIL PROTECTED]>
>Objet�: Re: Structure Alignment
>Date�: Mer 27 oct 1999 18:40
>
> Page 88 of the Code Warrior C Compiler Reference
> says:
>
> "power Align every field on its natural boundary
> . . . .
> For example, it aligns a character on a
> 1-byte boundary and a 16-bit integer on
> a 2-byte boundary."
>
> This suggests to me that what I did is safe, but there
> could be some gotchas that are not described in this
> part of the documentation. Does anyone know of any
> such gotchas?
>
> Greg Bungo
> [EMAIL PROTECTED]
> (630)949-3250 voice
> (630)949-3299 fax
>
> -----Original Message-----
> From: Roger Chaplin <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
> Date: Wednesday, October 27, 1999 11:32 AM
> Subject: Re: Structure Alignment
>
>
> "Greg Bungo" <[EMAIL PROTECTED]> wrote:
>> I'm porting a program from another platform to Palm,
>> and I encountered a structure alignment problem. The
>> default Palm CodeWarrior alignment is "68K". This
>> will make the size of a structure such as this
>>
>> typedef struct tagHDR
>> {
>> char Type[2];
>> char ID[8];
>> char Num[5];
>> char Time[6];
>> } HDR;
>>
>> 22 bytes rather than the expected 21 bytes.
>> I changed the Struct Alignment setting in
>> CodeWarrior to "PowerPC", and now this
>> structure is 21 bytes. This saves me from
>> rewriting some of our code, since there are places
>> in the program that depend on sizeof(HDR).
>>
>> My question: will this change of the alignment
>> setting cause problems on the Palm? If there
>> is no known reason why the "68K" alignment
>> type is needed, I would prefer the PowerPC
>> setting, since that will save us a few bytes,
>> and memory on the Palm is very precious.
>
> If the structure you show above is the only one, then no, it won't
> cause problems. However, regardless of the compiler settings, the
> MC68000 core CPU that's in the DragonBall requires even addresses when
> accessing data that is 16-bit or longer. Maybe a CodeWarrior expert
> needs to jump into this to explain exactly what PowerPC alignment does
> to that compiler (it obviously packs char data, but how does it align
> 16-bit or longer data types?). If PowerPC alignment does remove all
> padding, then something like
>
> struct foo
> { char a[5];
> int b;
> };
>
> would give you an address error when you try to access the b element.
>
> --
> Roger Chaplin
> <[EMAIL PROTECTED]>
>
>
>
>
>
