Re: [Swig-user] Documentation for wrapping data arrays?

[William S F. <ws...@fu...>]

Jake Janovetz wrote:
> Hey folks--
> 
> I recently had need to expand an existing SWIG wrapper from Python/Java to
> now include Ruby and C#.  The only challenging part is with functions like:
>    long read_data(long buffer_length, unsigned char *buffer);
>    long write_data(long buffer_length, unsigned char *buffer);
> 
> I have these wrapped in Python and Java, but looking for appropriate
> typemaps in C# has not been easy.  I know this subject has come up many many
> times, so I'm wondering if there is some centralized documentation for this
> particular subject that I'm missing.
> 
> I know there is the standard SWIG docs, but this seems to be a FAQ that is
> probably addressed somewhere.
> 
> If not, can someone provide an example of how they've wrapped such functions
> for C#?
> 

For C#, ideally, you'd use a multi-argument typemap, passing just the
one parameter (a uchar[]) from managed to unmanaged code. However,
you'll then be missing the array size in the unmanaged code. You could
make a callback into the managed side to extract this from the uchar[]
(managed side) unsigned char* (unmanaged side). See the char* or
std::string typemaps to get an idea how to add in a callback / delegate.

Alternatively, pass the array and size across the PInvoke layer. Don't
use multi-argument typemaps. Instead you can (optionally) make the proxy
method private (use %csmethodmodifiers) then add in another method on
the c# side (eg use the cscode typemap to add a method to a proxy class)
which has just the one parameter which in turn calls the private method.

William