All C data in CFFI is referenced through pointers. This includes defined C variables that hold immediate values, and integers.
To see why this is, consider the case of the C integer. It is not only an arbitrary representation for an integer, congruent to Lisp’s fixnums; the C integer has a specific bit pattern in memory defined by the C ABI. Lisp has no such constraint on its fixnums; therefore, it only makes sense to think of fixnums as C integers if you assume that CFFI converts them when necessary, such as when storing one for use in a C function call, or as the value of a C variable. This requires defining an area of memory11, represented through an effective address, and storing it there.
Due to this compartmentalization, it only makes sense to manipulate
raw C data in Lisp through pointers to it. For example, while there
may be a Lisp representation of a
struct that is converted to C
at store time, you may only manipulate its raw data through a pointer.
The C compiler does this also, albeit informally.
|• Basic Pointer Operations|
|• Allocating Foreign Memory|
|• Accessing Foreign Memory|
The definition of memory includes the CPU registers.