[plt-scheme] ffi question, _string/utf-16

Thanks, that puts me on the right track.  I had missed that  
`scheme_utf16_to_ucs4' function.

I had been using this, for a function type

     (_fun (n) :: (n : _int) (result : (_list o _uint16 n)) -> _void ->
                  (list->string (map integer->char result)))

But I don't know much about unicode either, and I'm not sure about  
integer->char... I thought there were times in utf16 when one  
character took 32 bits.

Rob


On Oct 30, 2007, at 1:06 AM, Jon Rafkind wrote:

> Robert Nikander wrote:
>> Hi,
>>
>> I have a C function like
>>
>> void get_chars(int n, uint16 *str);
>>
>> that fills the buffer 'str' with a utf-16 string. I'd like to call it
>> and end up with a Scheme string. It looks like the "_string/utf-16"
>> ctype knows how to do the conversion, but I don't see how to use  
>> it in
>> this case. Can I?
> It would be nice to use _string/utf-16 as an output type, but it  
> doesn't
> seem like thats provided. You can probably make a new custom type that
> converts between a sequence of 16-bit characters into regular scheme
> strings. I'll admit that I don't know much about unicode and its
> variations but the only function I could find in mzscheme that dealt
> with converting utf16 into something else was scheme_utf16_to_ucs4. I
> hacked this up
>
> void x( int x, unsigned char * q ){
> q[0] = 0;
> q[1] = 'b';
> q[2] = 0;
> q[3] = 'd';
> q[4] = 0;
> q[5] = 0;
> }
>
> (require (lib "foreign.ss"))(unsafe!)
>
> (define libx (ffi-lib "libx"))
>
> (define convert (get-ffi-obj "scheme_utf16_to_ucs4" #f (_fun _bytes  
> _int
> _int (out : (_bytes o length)) (length : _int) (_ptr o _int) _int ->
> _pointer -> out)))
>
> (define x (get-ffi-obj "x" libx (_fun (length : _int) (foo : (_bytes o
> (+ length 2))) -> _void -> (convert foo 0 length (+ length 1) 0))))
>
> (printf "~a\n" (x 6))
>
> mzscheme -vf x.ss
> Welcome to MzScheme v371 [3m], Copyright (c) 2004-2007 PLT Scheme Inc.
> bd
>
>
> `scheme_utf16_to_ucs4' is what the foreign library uses internally to
> convert utf16 into a scheme string.