1. Is there a way to associate a prop:custom-write to _cpointers or
instances of ctypes defined using define-cstruct? I want to expose C
data type instances as opaque values, whose printed representation
constructs them; e.g. I want this to happen:
> (mpfr-exp (mpfr 1))
(mpfr #e2.718281828459045235360287471352662497759)
where mpfr constructs instances of _mpfr_t from Racket reals. As it is,
I'm defining a struct wrapper, which seems like a pointless indirection.
2. There are a few cases where MPFR (the C library) allocates arrays and
returns pointers to them. I want to interpret them as strings, lists,
and vectors, but I also have to call "special free" functions to
deallocate the memory. This is the way I'm doing it (simplified):
(define gimme-string
(get-ffi-obj 'gimme_string libmpfr (_fun -> _pointer)))
@c{
char* cstr_id(char* p)
{
return p;
}
}
(define cstr->string
(get-ffi-obj-from-this 'cstr_id (_fun _pointer -> _string)))
(define cstr (gimme-string))
(define str (cstr->string cstr))
(special-free cstr)
It's silly. But I can't figure out another way to have the FFI library
interpret a char* pointer as a string AND give me access to the pointer
itself so I can free the memory. I get the impression that it's
possible, but I don't know the right incantations yet.
Neil T
(About the @c{...} syntax and get-ffi-obj-from-this: it means what you
think it does. I'm using a version of Jay's superc package, modified to
work on Linux. Yes, it's awesome.)
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