[Xapian-devel] C API

[Olly Betts]

On Thu, Sep 08, 2005 at 08:06:02AM -0500, Peter Karman wrote:
> My question is whether there exists a C API for Xapian, or more precisely, 
> whether anyone has successfully used Xapian from within a C program. I 
> realize that it is possible to use C++ libraries with C, but at a cursory 
> glance, it doesn't look as if the xapian-core C++ source is defined with 
> 'extern "C"' or any of the other common access points for C programs.

There isn't a C API.

The C++ API is almost entirely class based, so any fully featured C API
would inevitably involve passing around opaque handles which are in
reality pointers to C++ objects.  That always feels clumsy to me - I
think it makes more sense to just use C++ instead of trying to write OO
code in C.

A restricted C API might be feasible - if you only allowed one
WritableDatabase and one Document to exist at a time for example.  But
I'm not sure it's effort well spent really.

One option would be to write your own thin C++ wrapper around Xapian
which exports a simple C API with all the features you actually need for
your project.  I took roughly this approach for the gmane indexer to
allow me to bolt Xapian onto an existing C indexer quickly.

> A change to Swish-e to use Xapian would mean a total re-write for
> Swish-e, so we could do C++, but it would be good to know that
> upfront.
>
> All thoughts appreciated.

Another approach which comes to mind is to use something like python.
That rather rules out much hope of code reuse though.  At least with
C++, most existing C code could be reused with only minor changes,
or by compiling it as C and wrapping 'extern "C" {...}' around the
header.

Cheers,
    Olly