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

[Paul Whitfield]

A simpler way to achieve what you want MAY be to add the command line 
option for gcc

-fshort-enums

(Can't test this for your compiler type though!)

Regards

Paul
Fabio Giovagnini wrote:
> 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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