calling a D function from C and C++ code

[Bill Baxter]

Bedros Hanounik wrote:
> I'm a lot interested in D recently, and have been reading the
> documentation the wiki, forums, etc. But I could not find a place
> where it explains how to call a D function from C and C++ code
> 
> all the documentation...etc discusses how to bind an existing library
> to D code; which is the most common case, but how about building a
> brand new library written in D; can anyone write a C code (or C++) to
> interface this library in D.

Pretty easy conceptually, just make any functions you want to call from 
C/C++ be "extern(C)", makeing sure you don't use any funky D-only 
parameter types, and then write the equivalent C prototype in a header 
file for the C/C++ code to use (and extern "C" it for C++).

In practice on Windows there are a few other issues in that DMD 
generates libs that aren't compatible with MSVC or MinGW.  The libs are 
link-compatible with the output of the Digital Mars C/C++ compiler, 
though (DMC), which you already have if you installed DMD.  If you're 
using GDC, I think you'll also be ok.  MinGW generates MSVC-compatible 
libs, so the MinGW version of GDC should be ok.

I'm not sure how to handle it if you want to use DMD on Windows and call 
from something besides DMC (like MinGW or MSVC).  I think in that case 
your best bet is to create a DLL from the D code.  From there you should 
be able to use MSVC tools, MinGW tools or whatever to create an import 
lib in the proper format for the C/C++ compiler you want to use.

This is something I've been meaning to try out myself but actually 
haven't done it myself.  I know for instance Kirk uses DLLs to link D 
code into C/Python as a part of PyD.

Hope that helps.

--bb