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From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: ada binding
Date: Thu, 09 Feb 2006 20:34:59 +0100
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Date: 2006-02-09T20:34:59+01:00
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Szymon Guz wrote:

> Martin Krischik napisa?(a):
>> Szymon Guz wrote:
>> 
>>> Maciej Sobczak napisa?(a):
>>>> Szymon Guz wrote:
>>>>
>>>>> how to make an Ada binding for a "C++" class using this C layer ?
>>>> Basically, if the C++ class is not a template, but just plain "classic"
>>>> OO stuff, then you can write a wrapper around it in C, which will still
>>>> be OO, but without the syntax sugar of real class. Something along
>>>> this:
>>>>
>>>> // an existing C++ class:
>>>> class MyClass
>>>> {
>>>> public:
>>>>     void myFun();
>>>> };
>>>>
>>>> // a C wrapper:
>>>> extern "C"
>>>> void * MyClass_new()
>>>> {
>>>>     return new MyClass;
>>>> }
>>>>
>>>> extern "C"
>>>> void MyClass_delete(void *p)
>>>> {
>>>>     delete static_cast<MyClass*>(p);
>>>> }
>>>>
>>>> extern "C"
>>>> void MyClass_myFun(void *vp)
>>>> {
>>>>     MyClass *mcp = static_cast<MyClass*>(vp);
>>>>     mcp->myFun();
>>>> }
>>>>
>>>> // and so on.
>>>>
>>>> Depending on the level of isolation that you want to achieve and the
>>>> level of type safety that you want to retain, hiding the object behind
>>>> void* might or might not be the best choice, but this is to give you
>>>> the idea. Above, MyClass_new, MyClass_delete and MyClass_myFun are
>>>> plain C functions (you can extract their declarations to separate
>>>> header file) and you can interface them from just about any sensible
>>>> language in existence and from Ada in particular.
>>>>
>>>>
>>> OK, but what about using the class fields :
>>>
>>> class MyClass
>>> {
>>> public:
>>>    int X;
>>>    int *p_X;
>>> }
>>>
>>> and what about inheriting this from the class in Ada, is it possible ?
>> 
>> If you are planning to inheriting  then you need to directly bind to the
>> C++ class. Only one compiler offers that (GNAT). Start reading here:
>> 
>> http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gnat_rm/Pragma-CPP_005fClass.html
>> 
>> Martin
> 
> I know but I wander if I can do that using other compilers and with the
> middle layer written in C.

You would need to use proxy classes then. Just as much work :-(

Martin

-- 
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Ada programming at: http://ada.krischik.com