Binding to functions having reference parameter

Binding to functions having reference parameter

[Antonio L�pez]

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I am doing a binding to a Dll Using Win32 binding and I have a problem with
functions having reference parameters (an C array).

�How must I declare those parameters? (ada functions doesn't allow out
parameters)

One example:

Dll fucntion is declared as :

_API_EXTERN AiInt16 _API_DLL_FUNC ApiCmdBite (AiUInt8 bModule, AiUInt8 biu,
AiUInt8 sc, AiUInt8 bite_status[]);

And I declare:

subtype UCHAR is Interfaces.C.unsigned_char;

type UCHAR_Array2 is array (0 .. 1) of aliased UCHAR;

function ApiCmdBite ( bModule : My_Win32.UCHAR; biu : My_Win32.UCHAR; sc :
My_Win32.UCHAR;

bite_status : My_Win32.UCHAR_Array2 )

return My_Win32.SHORT;

However I get a warning: "bite_status" is never assigned a value, calling
the fucntion.

Obvius It needs to be done otherwise! Could you enlight me please?

I have tried to pass the parameter as bite_status :
Interfaces.C.unsigned_char'Address but I get the error: attribute "Address"
may not be used in a subtype mark

I should be able to use for example: 'bite_status(0) := 1;' or 'if
(bite_status(1) == 2)'

Re: Binding to functions having reference parameter

[Stephen Leake]

"Antonio L�pez" <alm@gtd.es.REMOVE> writes:

> I am doing a binding to a Dll Using Win32 binding and I have a problem with
> functions having reference parameters (an C array).
> 
> �How must I declare those parameters? (ada functions doesn't allow out
> parameters)

If you are using GNAT, read the user's guide, section The GNAT
Compilation Model | Mixed Language Programming | Calling Conventions.
This says that GNAT Convention C follows the Ada 95 Reference manual,
section B.3. That, in turn, says in paragraph 70:

      70. An Ada parameter of an array type with component type T, of
          any mode, is passed as a t* argument to a C function, where t
          is the C type corresponding to the Ada type T.

So just declare the corresponding Ada array, and it will be passed by
reference.

If you are not using GNAT, see if your compiler also follows B.3 (70).

-- 
-- Stephe

RE: Binding to functions having reference parameter

[Beard, Frank [Contractor]]

function ApiCmdBite ( bModule     : My_Win32.UCHAR;
                      biu         : My_Win32.UCHAR;
                      sc          : My_Win32.UCHAR;
                      bite_status : access My_Win32.UCHAR_Array2 );

return My_Win32.SHORT;

Then, the variable you have declared to pass to it needs to be
something like:

  new_bite_status : aliased My_Win32.UCHAR_Array2;

So, that when you call it, it will look something like

  return_code := ApiCmdBite ( bModule     => ???,
                              biu         => ???,
                              sc           => ???,
                              bite_status => new_bite_status'access);

Frank

-----Original Message-----
From: Antonio López [mailto:alm@gtd.es.REMOVE]
Sent: Wednesday, May 08, 2002 10:40 AM
To: comp.lang.ada@ada.eu.org
Subject: Binding to functions having reference parameter


I am doing a binding to a Dll Using Win32 binding and I have a problem with
functions having reference parameters (an C array).

¿How must I declare those parameters? (ada functions doesn't allow out
parameters)

One example:

Dll fucntion is declared as :

_API_EXTERN AiInt16 _API_DLL_FUNC ApiCmdBite (AiUInt8 bModule, AiUInt8 biu,
AiUInt8 sc, AiUInt8 bite_status[]);

And I declare:

subtype UCHAR is Interfaces.C.unsigned_char;

type UCHAR_Array2 is array (0 .. 1) of aliased UCHAR;

function ApiCmdBite ( bModule : My_Win32.UCHAR; biu : My_Win32.UCHAR; sc :
My_Win32.UCHAR;

bite_status : My_Win32.UCHAR_Array2 )

return My_Win32.SHORT;

However I get a warning: "bite_status" is never assigned a value, calling
the fucntion.

Obvius It needs to be done otherwise! Could you enlight me please?

I have tried to pass the parameter as bite_status :
Interfaces.C.unsigned_char'Address but I get the error: attribute "Address"
may not be used in a subtype mark

I should be able to use for example: 'bite_status(0) := 1;' or 'if
(bite_status(1) == 2)'



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