Re: Loading database from string (C API)

On Fri, Dec 06, 2013 at 02:57:21PM +0100, Jan Wielemaker wrote:
> Hu Edd,
> 
> On 12/06/2013 02:40 PM, Edd Barrett wrote:
> >Hi,
> >
> >I am writing a VM which embeds SWI-prolog using the C interface (I am
> >actually calling the SWI C interface via Python-CFFI, but it is all the
> >same).
> >
> >I need to be able to parse Prolog source code (in a C string) into the Prolog
> >database. Looking at the FFI documentation [1] I don't see an obvious way to do
> >this. I guess one way is to write the Prolog source code to a file and
> >construct a query to consult/1.
> 
> That will surely work :-)
> 
> >Maybe it is possible to write the code to a memory file and use load_file/2
> >to load from a stream, but that seems convoluted too.
> 
> You can do
> 
> 	load_files(mydata, [stream(Stream)]).
> 
> That will compile the file from Stream and claim it was loaded from a
> file named `mydata'.
> 
> So, the question becomes how to get a Prolog stream from a C string.
> You can do that using the stream API defined in SWI-Stream.h but still
> undocumented.  What you want is something like below.  The default
> encoding is ISO Latin 1.  See SWI-Stream.h for other values.
> 
> int
> open_stream(char *s, term_t t)
> { IOSTREAM *stream;
> 
>   stream = Sopen_string(NULL, s, strlen(s), "r");
>   stream->encoding = ENC_UTF8;
> 
>   return PL_unify_stream(t, stream);
> }

Thanks Jan.

Hopefully Python's CFFI will allow me to write my own C functions (up
until now I have just been calling yours in libpl). If not, I can build
a shared object with this stub in.

-- 
Best Regards
Edd Barrett

http://www.theunixzoo.co.uk