Hello,
I am a D newbie and my company makes heavy use of C. I would like to
demonstrate that the D language can be beneficial much more than Java.
My question is: is it possible to make a library, that is callable
from C? I guess i would have to write the corresponding .h file for
inclusion, with possibly a C-wrapper around the D classes.
Thank you for helping.

Alain

%u wrote:
> Hello,
> I am a D newbie and my company makes heavy use of C. I would like to
> demonstrate that the D language can be beneficial much more than Java.
> My question is: is it possible to make a library, that is callable
> from C? I guess i would have to write the corresponding .h file for
> inclusion, with possibly a C-wrapper around the D classes.
> Thank you for helping.
> 
> Alain

All you need is to use extern (C) on those functions you want to be callable from C.

D:

extern (C) void doStuff(int withThis) { ... }


C header:
void doStuff(int);

 - Gregor Richards

Gregor Richards wrote:
> %u wrote:
>> Hello,
>> I am a D newbie and my company makes heavy use of C. I would like to
>> demonstrate that the D language can be beneficial much more than Java.
>> My question is: is it possible to make a library, that is callable
>> from C? I guess i would have to write the corresponding .h file for
>> inclusion, with possibly a C-wrapper around the D classes.
>> Thank you for helping.
>>
>> Alain
> 
> All you need is to use extern (C) on those functions you want to be callable from C.
> 
> D:
> 
> extern (C) void doStuff(int withThis) { ... }
> 
> 
> C header:
> void doStuff(int);
> 
>  - Gregor Richards

There's more to it than that.

The D runtime will need to be initialized unless special care is taken to avoid anything that's going to touch the GC or anything else that requires initialization. (it's been a while since I looked at that part of phobos/ares.

You'll have to be careful to keep the interfaces to mutually compatible data types.  D doesn't prevent you from writing something like:

    extern (C) char[] someFunc(SomeClass a, SomeAlias b, SomeDelegate c)

Essentially all the extern C part does is drop the name mangling.

Don't let exceptions leak out of this D/C barrier.. C doesn't know anything about exceptions.  If instead of C you really meant C++, the same still applies except with dmd on windows.  Every other combination of language/compiler/os is currently incompatible, though I'd love to see this fixed.

There might be something else that needs to be handled as well, but those are the things that come to mind quickly.

Later,
Brad

== Quote from Brad Roberts (braddr@puremagic.com)'s article
> There's more to it than that.
> The D runtime will need to be initialized unless special care is
taken
> to avoid anything that's going to touch the GC or anything else that requires initialization. (it's been a while since I looked at that
part
> of phobos/ares.
> You'll have to be careful to keep the interfaces to mutually
compatible
> data types.  D doesn't prevent you from writing something like:
>      extern (C) char[] someFunc(SomeClass a, SomeAlias b,
SomeDelegate c)
> Essentially all the extern C part does is drop the name mangling. Don't let exceptions leak out of this D/C barrier.. C doesn't know anything about exceptions.  If instead of C you really meant C++,
the
> same still applies except with dmd on windows.  Every other
combination
> of language/compiler/os is currently incompatible, though I'd love
to
> see this fixed.
> There might be something else that needs to be handled as well, but
> those are the things that come to mind quickly.
> Later,
> Brad

All you warn me against seems reasonable. D being a higher-level
language than C, you have to down-grade it by writing a wrapper
around the D library in order to make it understandable by the C
application.
What i miss however is what you call the 'D runtime' initialisation.
Could you give a concrete example of what needs to be done.
Thanks in advance
Alain

Alain wrote:

> == Quote from Brad Roberts (braddr@puremagic.com)'s article
> > There's more to it than that.
> > The D runtime will need to be initialized unless special care is
> taken
> > to avoid anything that's going to touch the GC or anything else that requires initialization. (it's been a while since I looked at that
> part
> > of phobos/ares.
> > You'll have to be careful to keep the interfaces to mutually
> compatible
> > data types.  D doesn't prevent you from writing something like:
> >      extern (C) char[] someFunc(SomeClass a, SomeAlias b,
> SomeDelegate c)
> > Essentially all the extern C part does is drop the name mangling. Don't let exceptions leak out of this D/C barrier.. C doesn't know anything about exceptions.  If instead of C you really meant C++,
> the
> > same still applies except with dmd on windows.  Every other
> combination
> > of language/compiler/os is currently incompatible, though I'd love
> to
> > see this fixed.
> > There might be something else that needs to be handled as well, but
> > those are the things that come to mind quickly.
> > Later,
> > Brad
> 
> All you warn me against seems reasonable. D being a higher-level
> language than C, you have to down-grade it by writing a wrapper
> around the D library in order to make it understandable by the C
> application.
> What i miss however is what you call the 'D runtime' initialisation.
> Could you give a concrete example of what needs to be done.
> Thanks in advance
> Alain

The Win32 DLL in D article at digitalmars.com sums it up pretty well I think:

http://www.digitalmars.com/d/dll.html

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