On Friday, 15 September 2017 at 15:35:48 UTC, bitwise wrote:
On Friday, 15 September 2017 at 07:24:34 UTC, Jonathan M Davis
wrote:
On Friday, September 15, 2017 04:15:57 bitwise via
Digitalmars-d-learn wrote:
I translated the headers for FreeType2 to D, and in many
cases, enums are used as struct members.
If I declare an extern(C) enum in D, is it guaranteed to have
the same underlying type and size as it would for a C
compiler on the same platform?
extern(C) should have no effect on enums. It's for function
linkage, and enums don't even have an address, so they don't
actually end up in the program as a symbol. And since C's int
and D's int are the same on all platforms that D supports
(we'd have c_int otherwise, like we have c_long), any enum
with a base type of int (which is the default) will match
what's in C.
- Jonathan M Davis
I'm confused...is it only C++ that has implementation defined
enum size? I thought that was C as well.
I believe C enum size is implementation defined. A C compiler can
pick the underlying type (1, 2, or 4 bytes, signed or unsigned)
that fits the values in the enum.
A D int is always the same size as a C int because C ints are 4
bytes on 32bit and above architectures and D doesn't support
architectures below 32bit so you never run into a case where a C
int is 2 bytes.
D can't guarantee that the size of an extern(C) enum will match
an arbitrary C compiler's choice, so I'm pretty sure it'll just
default to a D int.
It's further likely that padding in a struct will differ between
C compilers so if you need a D struct to be the same size as a C
struct in every case... welp that's not exactly going to be fun.
