Wilco Greven <greven@kde.org> writes:
The example I gave was rather bad. Let me give a better one.
typedef struct { int a; short b; } TestStruct;
(defcstruct test-struct (a :int) (e :short))
The problem arose when I wanted to access elements in an array of structs. Say I have an array "TestStruct *tests". I expected to be able to access the individual elements of this array by
(inc-ptr tests (* (foreign-struct-size 'test-struct) array-index)
The problem is that (foreign-type-size 'test-struct) returns a size of 6, while sizeof(TestStruct) returns 8. Therefore the code above doesn't work correctly.
My guess was that this had something to do with alignment of the struct, but I have to admit that my knowledge about memory alignment is pretty much nil. zero.
Indeed this is a bug, but I probably won't have time to look at it for a little while... Probably foreign structure types need to sum the alignment of each member to calculate the total alignment of the structure (and I think there are some wrinkles with double float alignment on Darwin also). James