_array produces a ctype, not an actual array itself. To get an array you can create one with malloc or you can call a C function through the ffi.
If you use malloc then you get back a generic #<cpointer> type which you can convert to an array using ptr-ref as per the docs: "Since an array is treated like a struct, casting a pointer type to an array type does not work. Instead, use ptr-ref with a pointer, an array type constructed with _array, and index 0 to convert a pointer to a Racket representation that works with array-ref and array-set!." -> (require ffi/unsafe) -> (define t (_array _int 3)) -> (define x (malloc t)) -> (define a (ptr-ref x t 0)) -> a #<array> -> (array? a) #t -> (array-ref a 1) 1056768 -> (array-set! a 1 12) -> (array-ref a 1) 12 Or as an ffi function type (-> _int -> (_array _int 3)), although I didn't test that. On 12/13/2012 11:48 PM, ??? wrote: > in the reference, I see the _array function, but I don't understand well, > when i try to do, always output errors, can anyone give me an example? > here is my test in REPL: > > racket@> (_array _int 3) > #<ctype> > racket@> (array? (_array _int 3)) ; why? > #f > racket@> > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users
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