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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:

# extern (C) int myFunctionWrapper (char a, int b, char* c)
# {
#    return myFunction (a,b,c); // myFunction is a normal D function.
# }

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:
 
 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D function.
 # }
 
 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,



 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D function.
 # }



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,
 
 

 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D 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
May 27 2008
parent reply BCS <ao pathlink.com> writes:
Reply to Downs,


 BCS wrote:
 

 Reply to Matthias,
 

 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D
 function.
 # }



 I guess I known what to do at lunch today.



 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,


 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D
 function.
 # }



 I guess I known what to do at lunch today.



 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);}"
  );
 }
 
 



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,
 

 # extern (C) int myFunctionWrapper (char a, int b, char* c)
 # {
 #    return myFunction (a,b,c); // myFunction is a normal D
 function.
 # }



 I guess I known what to do at lunch today.



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



 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);}"
 );
 }



 
 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