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digitalmars.D.learn - Calling D functions from C

reply Pontus Pihlgren <pontus update.uu.se> writes:
Hi all.

Its a rather hypothetical I guess, but is it possible to call D 
functions from C? If so, are there limitations?

Kind Regards,
Pontus.
May 27 2008
next sibling parent Robert Fraser <fraserofthenight gmail.com> writes:
Pontus Pihlgren wrote:

 Hi all.
 
 Its a rather hypothetical I guess, but is it possible to call D 
 functions from C? If so, are there limitations?
 
 Kind Regards,
 Pontus.


extern(C) your D functions & enjoy! If you're not running the D garbage 
collector, don't rely on garbage collection happening (obvious), and a 
bit less obvious is that many libraries require their static 
constructors to be called, so be sure to run those first. Also, don't 
throw exceptions over D-C lines. There's probably other limitations I'm 
not thinking of/don't know of.
May 27 2008
prev sibling parent reply Matthias Walter <Matthias.Walter st.ovgu.de> writes:
Pontus Pihlgren Wrote:


 Hi all.
 
 Its a rather hypothetical I guess, but is it possible to call D 
 functions from C? If so, are there limitations?
 
 Kind Regards,
 Pontus.


If you want to really call the D function from C code, compiling with a C
compiler, this can get tricky, as the C compiler normally does not know the ABI
of D. It therefore does not know in which registers / stack slots to put which
argument, etc.

But you can write a Wrapper routine in D which simply calls your D routine but
has an extern (C) calling convention:






With this code you can call myFunctionWrapper from your C code like you do
normally. Alternatively you can code all your C stuff in a .d file, putting
extern (C) around everything. Then you can call it without a wrapper, too.

best regards
Matthias Walter
May 27 2008
next sibling parent Pontus Pihlgren <pontus update.uu.se> writes:
Matthias Walter skrev:

 Pontus Pihlgren Wrote:
 

 Hi all.

 Its a rather hypothetical I guess, but is it possible to call D 
 functions from C? If so, are there limitations?

 Kind Regards,
 Pontus.


 
 If you want to really call the D function from C code, compiling with a C
compiler, this can get tricky, as the C compiler normally does not know the ABI
of D. It therefore does not know in which registers / stack slots to put which
argument, etc.
 
 But you can write a Wrapper routine in D which simply calls your D routine but
has an extern (C) calling convention:
 




 
 With this code you can call myFunctionWrapper from your C code like you do
normally. Alternatively you can code all your C stuff in a .d file, putting
extern (C) around everything. Then you can call it without a wrapper, too.
 
 best regards
 Matthias Walter


That sound almost to easy, I thought that extern could only refer to, 
you know, external functions and not to declare new functions.

Looking more closely at the documentation at 
http://www.digitalmars.com/d/2.0/interfaceToC.html verifies it :) I 
guess I must have missed it the first time I read it.

Thanks,
Pontus.
May 27 2008
prev sibling parent reply BCS <ao pathlink.com> writes:
Reply to Matthias,









that deserves a template. 

I guess I known what to do at lunch today.
May 27 2008
parent reply downs <default_357-line yahoo.de> writes:
BCS wrote:

 Reply to Matthias,
 
 







 
 that deserves a template.
 I guess I known what to do at lunch today.
 
 


template Forward(string NAME) {
  mixin("extern(C) ReturnType!(&"~NAME~")
c_"~NAME~"(ParameterTypeTuple!(&"~NAME~") p) {
    return "~NAME~"(p);
  }");
}

Untested, but should work.

 --downs
May 27 2008
parent reply BCS <ao pathlink.com> writes:
Reply to Downs,


 BCS wrote:
 

 Reply to Matthias,
 




 function.



 that deserves a template.
 I guess I known what to do at lunch today.


 template Forward(string NAME) {
 mixin("extern(C) ReturnType!(&"~NAME~")
 c_"~NAME~"(ParameterTypeTuple!(&"~NAME~") p) {
 return "~NAME~"(p);
 }");
 }
 Untested, but should work.
 
 --downs
 


maybe, I'd kind rather not use a mixin for that. (I avoid them wherever I 
can) I'll take real a pass at it later.

On second look it seem the mixin is needed to make the name work but it seem 
to be over kill for the rest

// untested
template Forward(alias NAME)
{
  mixin(
   "extern(C) ReturnType!(&NAME) c_"~NAME.stringof~"(ParameterTypeTuple!(&NAME) 
p) { return NAME(p);}"
  );
}
May 27 2008
parent reply downs <default_357-line yahoo.de> writes:
BCS wrote:

 Reply to Downs,
 

 BCS wrote:


 Reply to Matthias,





 function.



 that deserves a template.
 I guess I known what to do at lunch today.


 template Forward(string NAME) {
 mixin("extern(C) ReturnType!(&"~NAME~")
 c_"~NAME~"(ParameterTypeTuple!(&"~NAME~") p) {
 return "~NAME~"(p);
 }");
 }
 Untested, but should work.

 --downs


 
 maybe, I'd kind rather not use a mixin for that. (I avoid them wherever
 I can) I'll take real a pass at it later.
 
 On second look it seem the mixin is needed to make the name work but it
 seem to be over kill for the rest
 
 // untested
 template Forward(alias NAME)
 {
  mixin(
   "extern(C) ReturnType!(&NAME)
 c_"~NAME.stringof~"(ParameterTypeTuple!(&NAME) p) { return NAME(p);}"
  );
 }
 
 


Remember. stringof is not guaranteed to be in any sort of sane format.
For example, the above code would fail if it for some obscure reason contains
spaces (or other invalid characters).
If you let the user pass a string, at least you know where the blame lies.

 --downs
May 28 2008
parent BCS <ao pathlink.com> writes:
Reply to Downs,


 BCS wrote:
 

 Reply to Downs,
 

 BCS wrote:
 

 Reply to Matthias,
 




 function.



 that deserves a template.
 I guess I known what to do at lunch today.


 template Forward(string NAME) {
 mixin("extern(C) ReturnType!(&"~NAME~")
 c_"~NAME~"(ParameterTypeTuple!(&"~NAME~") p) {
 return "~NAME~"(p);
 }");
 }
 Untested, but should work.
 --downs
 


 maybe, I'd kind rather not use a mixin for that. (I avoid them
 wherever I can) I'll take real a pass at it later.
 
 On second look it seem the mixin is needed to make the name work but
 it seem to be over kill for the rest
 
 // untested
 template Forward(alias NAME)
 {
 mixin(
 "extern(C) ReturnType!(&NAME)
 c_"~NAME.stringof~"(ParameterTypeTuple!(&NAME) p) { return NAME(p);}"
 );
 }


 Remember. stringof is not guaranteed to be in any sort of sane format.
 
 For example, the above code would fail if it for some obscure reason
 contains spaces (or other invalid characters).
 
 If you let the user pass a string, at least you know where the blame
 lies.
 
 --downs
 


// untested
template Forward(alias fn, char[] name)
{
mixin(
"extern(C)ReturnType!(&NAME)"~name~"(ParameterTypeTuple!(&fn) p){return fn(p);}"
);
}
May 28 2008