Re: Loading database from string (C API)

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);
}

	Enjoy --- Jan
	
> P.S. Typo in documentation:
> "security riscs" -> "security risks"
> http://www.swi-prolog.org/pldoc/man?section=memory-files

Thanks.  Fixed (will be on the site next release).

>
> [1] http://www.swi-prolog.org/pldoc/man?section=foreign
>