Error when passing struct by value

[Liam Healy]

Looks like you're sending it a list of symbols 'read-func etc.
'(read-func seek-func (null-pointer) tell-func)
is a list of two symbols, a list, then another symbol. It needs to be
a plist (property list) with alternating slot names and values
(list 'read-func read-func 'seek-func seek-func...)
(At the moment I can't remember if the slot names are in the keyword
package or not, so you might need :read-func instead of 'read-func
etc.)

Liam

On Thu, Apr 30, 2015 at 7:28 PM, Marshall Mason
<marshallmason2 at gmail.com> wrote:
> Hello,
> I'm using SBCL version 1.2.4, CFFI version 0.14.0, and libffi version 3.1.
> I've been trying to pass a struct by value using CFFI and libffi. I'm a
> newbie to both CFFI and Lisp so I had to piece this together from the manual
> as well as some of the unit tests that come with CFFI. I'm getting an error
> that I just can't get past:
>
> The value READ-FUNC is not of type SB-SYS:SYSTEM-AREA-POINTER
>
> The library I'm trying to wrap is libvorbisfile, which decodes Ogg Vorbis
> files. It has an init function called ov_open_callbacks:
>
> int ov_open_callbacks(void *datasource, OggVorbis_File *vf, const char
> *initial, long ibytes, ov_callbacks callbacks);
>
> The part it's choking on is the last argument, a struct, passed by value, of
> callback functions:
>
> typedef struct {
>     size_t (*read_func)  (void *ptr, size_t size, size_t nmemb, void
> *datasource);
>     int    (*seek_func)  (void *datasource, ogg_int64_t offset, int whence);
>     int    (*close_func) (void *datasource);
>     long   (*tell_func)  (void *datasource);
> } ov_callbacks;
>
> The library is designed to use one of a few static structs defined in a
> header file. Since it's defined in the header file and not in
> libvorbisfile.so, I must create CFFI translation code. There were a lot of
> other structs I had to wrap with CFFI as well. Here is my code:
>
> http://pastie.org/10122885
>
> Does anyone have any clues about what I'm doing wrong here?
>
> (Regarding my previous email about getting CFFI working on Debian jessie, it
> turns out the Debian version of cl-alexandria is missing a file and cl-cffi
> is buggy, so I just added the missing file and installed the CFFI source by
> hand. Thanks for the response, Fau.)
>
> Marshall