Question about -ansi flag, and different size of struct from C and C++

Sergei Organov osv at
Mon Dec 15 12:55:37 UTC 2003

Oleg Ivanov <Belinus at> writes:
>     Hello list,
>     I have a problem. I defined struct like:
>         struct dummy {
>           int var1;
>           short var2;
>           int var3;
>        } __attribute__ ((packed));
>     and access to it from C and C++ code.
>     The problem is that size from C is 10 bytes and from C++ is 12 bytes, I
>     couldn't make that C++ packed that struct, exept removing -ansi flag from
>     compiler string.
When you rely on such a non-standard feature as 'packed struct', there is
absolutely no reason to give -ansi flag to the compiler. I believe the sole
purpose of -ansi flag while compiling RTEMS is a [weak] attempt to make sure
the sources are ANSI C and don't have any GNUisms.

>     So I have two question, is there another method to ask C++ packed struct,
>     and do we really need -ansi flag to compile rtems ?

I think you can remove -ansi flag.

Anyway, as far as I remember, once I've solved similar problem by defining a
structure like this:

typedef struct {
} __attribute__((packed)) dummy;


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