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digitalmars.D.learn - Example of using C API from D?

reply Russel Winder <russel winder.org.uk> writes:
I am rewriting a C++ program in D, but need to access a C library that
has no D binding: this is a GtkD based program which has a Pango
binding, but Pango doesn't offer the information I need, that is hidden
in the underlying Fontconfig C API.

I could create a complete D binding for Fontconfig using the GIR files
but that seems a bit over the top.=20

Can anyone point me at an example of a D program using a C API that has
structs, enums and functions so I can see if I just hack enough for my
use or go on to the full binding activity.

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk
Sep 02 2018
next sibling parent reply rikki cattermole <rikki cattermole.co.nz> writes:
On 03/09/2018 12:52 AM, Russel Winder wrote:

 I am rewriting a C++ program in D, but need to access a C library that
 has no D binding: this is a GtkD based program which has a Pango
 binding, but Pango doesn't offer the information I need, that is hidden
 in the underlying Fontconfig C API.
 
 I could create a complete D binding for Fontconfig using the GIR files
 but that seems a bit over the top.
 
 Can anyone point me at an example of a D program using a C API that has
 structs, enums and functions so I can see if I just hack enough for my
 use or go on to the full binding activity.
 


You don't need to create a complete binding for something to use a 
subset of it.

Writing up a Derelict style binding is easy enough since e.g. SharedLib 
struct handles most of the work (from util package).

https://github.com/DerelictOrg/DerelictUtil/blob/master/source/derelict/util/sharedlib.d#L118
Sep 02 2018
parent reply Russel Winder <russel winder.org.uk> writes:
On Mon, 2018-09-03 at 01:00 +1200, rikki cattermole via Digitalmars-d-
learn wrote:

=20


[=E2=80=A6]

 You don't need to create a complete binding for something to use a=20
 subset of it.


True, but all too often you find there are so many interdependencies of
names, you end up binding most of the API. I tried fiddling with
Fontconfig using Python which has no binding and was able to hack up
just enough using CFFI to get things working. So I think in this case a
subset for the application is feasible =E2=80=93 as opposed to creating a
complete binding.=20


 Writing up a Derelict style binding is easy enough since e.g.
 SharedLib=20
 struct handles most of the work (from util package).
=20
=20


https://github.com/DerelictOrg/DerelictUtil/blob/master/source/derelict/uti=
l/sharedlib.d#L118

I am not convinced this is a good approach since you do not get the
signatures at compile time. The advantage of a binding, or subset of a
binding is that you get full compiler support.

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk
Sep 02 2018
parent reply rikki cattermole <rikki cattermole.co.nz> writes:
On 03/09/2018 5:07 AM, Russel Winder wrote:

 On Mon, 2018-09-03 at 01:00 +1200, rikki cattermole via Digitalmars-d-
 learn wrote:


 […]

 You don't need to create a complete binding for something to use a
 subset of it.


 
 True, but all too often you find there are so many interdependencies of
 names, you end up binding most of the API. I tried fiddling with
 Fontconfig using Python which has no binding and was able to hack up
 just enough using CFFI to get things working. So I think in this case a
 subset for the application is feasible – as opposed to creating a
 complete binding.


You won't need to actually fill out any c struct's that you don't need 
either. Make them opaque as long as they are referenced via pointer and 
not by value.


 Writing up a Derelict style binding is easy enough since e.g.
 SharedLib
 struct handles most of the work (from util package).


 https://github.com/DerelictOrg/DerelictUtil/blob/master/source/derelict/util/sharedlib.d#L118
 
 I am not convinced this is a good approach since you do not get the
 signatures at compile time. The advantage of a binding, or subset of a
 binding is that you get full compiler support.


Ugh, you do know that the linker which does all the hard work doesn't 
know anything about the signature of the C function? That is the part 
SharedLib replaces. You will of course define it with a proper signature 
on D's side with a helpful cast :)

i.e. 
https://github.com/DerelictOrg/DerelictGL3/blob/master/source/derelict/opengl/versions/gl1x.d



 Sep 02 2018



  parent  Russel Winder <russel winder.org.uk>  writes:


On Mon, 2018-09-03 at 11:41 +1200, rikki cattermole via Digitalmars-d-learn
wrote:
[=E2=80=A6]

=20
 You won't need to actually fill out any c struct's that you don't need=


=20

 either. Make them opaque as long as they are referenced via pointer and=


=20

 not by value.


True. And indeed Fontconfig can mostly meet the "it's an opaque type based
system" but there are a few dark corners =E2=80=93 most of which I need!=
=20

[=E2=80=A6]

=20
 Ugh, you do know that the linker which does all the hard work doesn't=20
 know anything about the signature of the C function? That is the part=20
 SharedLib replaces. You will of course define it with a proper signature=


=20

 on D's side with a helpful cast :)


Not good enough to be honest, D is a statically typed language and so all
usage of functions should be checked against something other than a human
guess.

Anyway DStep has given me a Fontconfig D module that works nicely, and I wi=
ll
check dpp as an alternative as soon as it builds on Debian Sid.
=20
--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 06 2018



prev sibling  parent reply Arun Chandrasekaran <aruncxy gmail.com>  writes:


On Sunday, 2 September 2018 at 12:52:11 UTC, Russel Winder wrote:

 I am rewriting a C++ program in D, but need to access a C 
 library that has no D binding: this is a GtkD based program 
 which has a Pango binding, but Pango doesn't offer the 
 information I need, that is hidden in the underlying Fontconfig 
 C API.

 I could create a complete D binding for Fontconfig using the 
 GIR files but that seems a bit over the top.

 Can anyone point me at an example of a D program using a C API 
 that has structs, enums and functions so I can see if I just 
 hack enough for my use or go on to the full binding activity.


You can look at zmqd[1] as an example. I've been using it in 
production. I've also used dstep[2] to translate C headers to D.

[1] https://github.com/kyllingstad/zmqd
[2] https://github.com/jacob-carlborg/dstep



 Sep 02 2018



 next sibling parent  Russel Winder <russel winder.org.uk>  writes:


On Sun, 2018-09-02 at 15:40 +0000, Arun Chandrasekaran via Digitalmars-
d-learn wrote:

 [=E2=80=A6]
=20
 You can look at zmqd[1] as an example. I've been using it in=20
 production. I've also used dstep[2] to translate C headers to D.
=20
 [1] https://github.com/kyllingstad/zmqd
 [2] https://github.com/jacob-carlborg/dstep


zmqd itself is just a thin D wrapper around deimos.zmq which is where
the C stuff is. Looks like a lot of repetition, and it is manual =E2=80=93 =
but
very useful for the task of the moment, so thanks for the pointer. For
0MQ, using DStep might be better than the hand crafted zmqd/diemos.zmq.
I am not sure if DStep is the right tool for creating a complete D
binding to Fontconfig. Given that Fontconfig has a GIR file, using
girtod may well be the better route.=20

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 02 2018



prev sibling next sibling parent  Russel Winder <russel winder.org.uk>  writes:


On Sun, 2018-09-02 at 18:11 +0100, Russel Winder wrote:

 [=E2=80=A6]
 I am not sure if DStep is the right tool for creating a complete D
 binding to Fontconfig. Given that Fontconfig has a GIR file, using
 girtod may well be the better route.=20


It turns out that the GIR file is not usable, and so the girtod route
is not feasible. I shall try the DStep route. Failing that it seems
there is

https://github.com/WebFreak001/fontconfig-d

which is a manual transform of a snapshot of the C API, so not an ideal
way, but a definite backstop position. It seems someone has trodden the
"using Fontconfig in D" path before me.

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 02 2018



prev sibling  parent reply Russel Winder <russel winder.org.uk>  writes:


On Sun, 2018-09-02 at 18:28 +0100, Russel Winder wrote:

=20


[=E2=80=A6]

 It turns out that the GIR file is not usable, and so the girtod route
 is not feasible. I shall try the DStep route. Failing that it seems
 there is
=20
 https://github.com/WebFreak001/fontconfig-d
=20
 which is a manual transform of a snapshot of the C API, so not an
 ideal
 way, but a definite backstop position. It seems someone has trodden
 the
 "using Fontconfig in D" path before me.


I compiled DStep master/HEAD (v0.2.3-16-g1308991) against LLVM 6.0 and
it seems to have done a rather splendid job of creating a D binding to
Fontconfig. Low-level obviously, but Fontconfig is seriously low level
anyway.

Now to work out how to make the project auto generate this D module so
as to avoid having it in the repository, and potentially inconsistent
with the platform in use.

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 02 2018



  parent reply Laeeth Isharc <Laeeth laeeth.com>  writes:


On Sunday, 2 September 2018 at 17:49:45 UTC, Russel Winder wrote:

 On Sun, 2018-09-02 at 18:28 +0100, Russel Winder wrote:

 


 […]

 It turns out that the GIR file is not usable, and so the 
 girtod route is not feasible. I shall try the DStep route. 
 Failing that it seems there is
 
 https://github.com/WebFreak001/fontconfig-d
 
 which is a manual transform of a snapshot of the C API, so not 
 an
 ideal
 way, but a definite backstop position. It seems someone has 
 trodden
 the
 "using Fontconfig in D" path before me.


 I compiled DStep master/HEAD (v0.2.3-16-g1308991) against LLVM 
 6.0 and it seems to have done a rather splendid job of creating 
 a D binding to Fontconfig. Low-level obviously, but Fontconfig 
 is seriously low level anyway.

 Now to work out how to make the project auto generate this D 
 module so as to avoid having it in the repository, and 
 potentially inconsistent with the platform in use.


You could also look at dpp. That's worked for most things I tried 
and was written in part to avoid the problem of macros changing 
behaviour at build time.

Example here:

https://run.dlang.io/?compiler=dmd&source=%23include%20<stdio.h>%0Avoid%20main()%20%7B%0A%20%20%20%20printf("Hello%20dpp.");%0A%7D

https://github.com/atilaneves/dpp



 Sep 02 2018



  parent reply Russel Winder <russel winder.org.uk>  writes:


On Sun, 2018-09-02 at 21:54 +0000, Laeeth Isharc via Digitalmars-d-
learn wrote:

 On Sunday, 2 September 2018 at 17:49:45 UTC, Russel Winder wrote:

=20




[=E2=80=A6]

 Now to work out how to make the project auto generate this D=20
 module so as to avoid having it in the repository, and=20
 potentially inconsistent with the platform in use.




Turns out this is easy with Meson and SCons. Dub is giving some issues.
:-(


 You could also look at dpp. That's worked for most things I tried=20
 and was written in part to avoid the problem of macros changing=20
 behaviour at build time.
=20
 Example here:
=20
=20


https://run.dlang.io/?compiler=3Ddmd&source=3D%23include%20<stdio.h>%0Avoid=
%20main()%20%7B%0A%20%20%20%20printf("Hello%20dpp.");%0A%7D

=20
 https://github.com/atilaneves/dpp


Interesting alternative to DStep. I came to D to avoid #include, but=E2=80=
=A6
I'll give it a whirl once I can get it compiled on Debian Sid. It seems
the libclang-dev package does not install a libclang.so symbolic link,
you have to be explicit about which version you want, e.g. libclang-
6.0.so on my Debian Sid installation.

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 03 2018



  parent reply Andrea Fontana <nospam example.com>  writes:


On Monday, 3 September 2018 at 10:50:17 UTC, Russel Winder wrote:

 Interesting alternative to DStep. I came to D to avoid 
 #include, but… I'll give it a whirl once I can get it compiled 
 on Debian Sid. It seems the libclang-dev package does not 
 install a libclang.so symbolic link, you have to be explicit 
 about which version you want, e.g. libclang- 6.0.so on my 
 Debian Sid installation.


I use dpp to generate d code to import:
- Create a temp.dpp file with #include inside
- Run "d++ --preprocess-only temp.dpp"

Now you have your .d file exactly like in dstep.

Andrea



 Sep 03 2018



  parent  Russel Winder <russel winder.org.uk>  writes:


On Mon, 2018-09-03 at 12:45 +0000, Andrea Fontana via Digitalmars-d-
learn wrote:

 [=E2=80=A6]
=20
 I use dpp to generate d code to import:
 - Create a temp.dpp file with #include inside
 - Run "d++ --preprocess-only temp.dpp"
=20
 Now you have your .d file exactly like in dstep.
=20


So where does this leave DStep if DPP is the next generation tool?

Of course I can create a dstep executable, but cannot yet create a d++
executable on Debian Sid. :-(

--=20
Russel.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk



 Sep 03 2018