> Is there a way to declare a field of a struct as a 24-bit integer in
> GCC?
Well, I think there is: as you wrote it down.
Write a simple example function and compile it with your options, but instead
of using "-c" (for compiling) please use "-S" (for stop after generating
assembler). The output file contains the assembler code which you can examine
for correct working.
My suggestion is this source:
typedef struct {
int a:1;
int b:3;
long c:24;
} T __attribute__((packed));
int get_size(void) {
return sizeof(T);
}
int get_a(T *t) {
return t->a;
}
int get_b(T *t) {
return t->c;
}
long get_c(T *t) {
return t->c;
}
> Barring that, do I have any guarantees about the order and
> packing of bitfields,
The standard (ISO) does _NOT_ guarantee order or packing. You may want to tag
your source with an "#ifdef" for the compiler. And you need the attribute
like shown above to get the elements packed, please see the GCC
documentation.
HTH, Bodo
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