Re: QUESTION: strange behaviour of typedef enum and __attribute__((packed)) using sh-hms-g++ 3.0.3

[Fabio Giovagnini <fgiovag at tin dot it>]

Alle 10:02, mercoledì 11 dicembre 2002, Michael Svetlik ha scritto:
> Fabio Giovagnini wrote:
> >Hi everybody,
> >that's my problem:
> >if I define
> >typedef struct ms{
> >	unsigned long f1;
> >	unsigned long f2;
> >	unsigned char f3;
> >	} __attribute__((packed)) ms_t;
> >
> >unsigned char test;
> >
> >...
> >...
> >test = sizeof(ms_t);
> >...
> >...
> >
> >i see test == 9;
> >
> >if I delete attribure specifier, i see test = 12.
> >This is the expected behaviour !!!!
> >
> >If I define
> >typedef enum en {em_f1 = 0, em_f2, em_f3}
> > __attribute__(((packed),aligned(1))) em_t;
> >
> >compiling with sh-hms-g++ 3.0.3 I have an error: missing semicolon ....
> >instead compiling with sh-hms-gcc 3.0.3 everything works fine and the size
> > is the expected size.
> >
> >If I define
> >typedef enum en {em_f1 = 0, em_f2, em_f3} em_t
> >__attribute__((packed,aligned(1)));
> >
> >no compiler error I see with sh-hms-g++ but the size is 4 that's
> > unexpected size for this enum type if we suppose the __attribute__
> > keyword has been working.
>

sorry, that's the rigth sintax: __attribute__((packed,aligned(1)))



> I tried to compile the above statement with i686-linux-gnu gcc 2.95.3,
> with g++ 2.95.3 and with g++ 3.1 - each of them from gnu.org, and each
> of them returned an error - you have a tricky compiler.
> What's the sense of packing a singular, scalar data type ? Do you want
> to zip it :-?

The sense is to save bytes if my enum type is lower than 255 values; I develop 
for embedded systems with few kbytes of ram;

> What does your HITACHI do, when accessing a data type, bigger than one
> byte, on an even address (aligned(1)) ?

When I'm sure my enum type is lower than 255 values, an unsigned char is 
enougth.

> You dont expect a size of 4 for your enum - what's the sizeof(int) on
> your machine ?
my sizeof(int) in 4, but I'd like to give my enum sizeof(unsigned char), and 
using gcc I can.

Thanks.


>
> >So I dedice the __attribute__ working in thuis sintax is not working, as
> >someone said some time ago.
> >
> >Does anyone have some tips to understand and solve this problem?
> >
> >Regards.
> >
> >
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