[Haskell-cafe] Fwd: c2hs: E.g. #include <iostream> OK in *.cpp's, but not in *.h's

[Nick Rudnick]

Ian, thanks a lot :-)

In fact I have a quite elaborate C++ backend to deal with – so your
recommendation of fficxx is highly welcome... :-) :-) :-)

Cheers, Nick

BTW: For everybody trying out the way described before, please enclose
declarations by

#ifdef __cplusplus
extern "C" {
#endif
...
#ifdef __cplusplus
}
#endif

in the *.hpp, too, to prevent an error.



2014-04-07 15:43 GMT+02:00 Ian Ross <ian at skybluetrades.net>:

> More or less.  Basically, C2HS is *C* FFI tool only.  If you get into a
> situation where C2HS can see C++ header files, it's not going to work.  How
> you get around that is up to you.  If your C++ library isn't too
> complicated, a C wrapper as used in hsqml seems like a good choice, or you
> can write the Haskell FFI import declarations yourself.  If your C++
> library is complicated and you really want to get at all of its public
> interface, you could try using a real C++ FFI tool (the only one I've
> really heard anything about is fficxx: http://ianwookim.org/fficxx/).
>
>
> On 7 April 2014 15:33, Nick Rudnick <nick.rudnick at gmail.com> wrote:
>
>>
>>
>> ---------- Forwarded message ----------
>> From: Nick Rudnick <nick.rudnick at gmail.com>
>> Date: 2014-04-07 15:28 GMT+02:00
>> Subject: Re: [Haskell-cafe] c2hs: E.g. #include <iostream> OK in *.cpp's,
>> but not in *.h's
>> To: Ian Ross <ian at skybluetrades.net>
>>
>>
>> Hi Ian,
>>
>> thanks for clearing up :-)
>>
>> So you mean the trick of hsqml primarily is
>>
>> (A) dummy typedefs to char, e.g.:
>>
>>  typedef char HsQMLStringHandle;
>>
>> (B) 'extern' sigantures, e.g.:
>> extern void hsqml_init_string(HsQMLStringHandle*);
>>
>> THIS WORKS...
>>
>> Occasionally, one might use two headers, e.g. a *.hpp as actual C++
>> header neither listed in the *.cabal nor the *.chs, where instead it would
>> be represented by a *.h, as described above.
>>
>> No more...??
>>
>> Thanks and cheers, Nick
>>
>>
>>
>>
>>
>>
>>
>> 2014-04-07 14:04 GMT+02:00 Ian Ross <ian at skybluetrades.net>:
>>
>> Hi Nick,
>>>
>>> As far as I can tell from a quick look at hsqml, the stuff in Setup.hs
>>> isn't related to C2HS.  What's more relevant is that hsqml defines a C
>>> library wrapper around the C++ library it uses -- C2HS is only used on that
>>> C wrapper, not on the C++ library itself.  In general, C2HS doesn't support
>>> C++ at all, because it needs to be able to parse the header files that it
>>> includes and we use the C parser from the languagge-c package to do that.
>>>  Any C++ constructs will just cause breakage.  And your "old school" FFI
>>> definition doesn't look in any header files, which is why it has no trouble.
>>>
>>> Basically, if you want to do something like what hsqml does, just take a
>>> look in the cbits directory there, in particular at hsqml.h which is the
>>> header that defines the C wrapper around the C++ library.  This hsqml.h
>>> header is the one that's included in the C2HS files.  If you want to wrap a
>>> C++ library directly, C2HS probably isn't the tool for the job.  I know
>>> there was some work during the last GSOC on a C++ FFI wrapper, but I don't
>>> know if anything concrete came of it.
>>>
>>> Cheers,
>>>
>>> Ian.
>>>
>>>
>>>
>>> On 6 April 2014 20:22, Nick Rudnick <nick.rudnick at gmail.com> wrote:
>>>
>>>> Dear all,
>>>>
>>>> maybe this is a piece of c2hs behaviour I missed to understand, but it
>>>> appears happening with C++ style includes deep in the header call hierarchy
>>>> – in case of a such backend C++ library, if one wishes to refer to by *.h's
>>>> in c2hs (e.g. for access to types of it), one might have a problem.
>>>>
>>>> - 8< cSample.h ---------------------------------------------
>>>> #include <iostream> ///////// here, with c2hs, leading to build abort
>>>> #ifdef __cplusplus
>>>> extern "C" {
>>>> #endif
>>>> void sampleFunction();
>>>> #ifdef __cplusplus
>>>> }
>>>> #endif
>>>> - 8< cSample.cpp ---------------------------------------------
>>>> #include "cSample.h"
>>>>  #include <iostream> ///////// here no problem
>>>>
>>>> void sampleFunction(){
>>>>   std::cout << "OK" << std::endl;
>>>> }
>>>> - 8< ----------------------------------------------------------------
>>>>
>>>> While 'old school' FFI (foreign import ccall) handles this
>>>> effortlessly, c2hs uses to abort with an exception like
>>>> C/cSample.h:3:20: fatal error: iostream: No such file or directory
>>>> compilation terminated.
>>>>
>>>> I see that hsqml gets around this, but apparently by tweaking Setup.hs
>>>> in a way not quite trivial – would this be necessary in any case, or are
>>>> there simpler alternatives?
>>>>
>>>> Please excuse if I oversaw something, but I am afraid I didn't see this
>>>> interesting issue covered elsewhere.
>>>>
>>>> Thank you a lot in advance & cheers, Nick
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Haskell-Cafe mailing list
>>>> Haskell-Cafe at haskell.org
>>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>>
>>>>
>>>
>>>
>>> --
>>> Ian Ross   Tel: +43(0)6804451378   ian at skybluetrades.net
>>> www.skybluetrades.net
>>>
>>
>>
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe at haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
>
>
> --
> Ian Ross   Tel: +43(0)6804451378   ian at skybluetrades.net
> www.skybluetrades.net
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140407/58c4a527/attachment.html>