difference between cffi mem-ref/mem-aref

[sinnatagg]

What is the difference between these two cffi functions? The fine manual is rather terse about this and I haven't managed to make them do something different yet.


-a

[Ramarren]

The manual is quite explicit on the difference:

The mem-aref function is similar to mem-ref but will automatically calculate the offset from an index.

To elaborate, the optional argument to those functions is treated differently, in mem-ref the offset is in bytes, but in mem-aref the offset is the index multiplied by the size of referenced type.

Looking at the code this is in fact the only functional difference:

Code: Select all

(defun mem-aref (ptr type &optional (index 0))
  "Like MEM-REF except for accessing 1d arrays."
  (mem-ref ptr type (* index (foreign-type-size type))))

Although there are compiler macros which implement optimizations if TYPE and/or INDEX are constant.

[sinnatagg]

Thanks, didn't think of looking at the source


-a