Re: Thick Ada bindings to C Win32

[Brian May <bam@snoopy.apana.org.au>]

>>>>> "Brian" == Brian May <bam@snoopy.apana.org.au> writes:

    Brian> I seem to remember that I encountered problems doing things
    Brian> as simply as you suggest, but I can't remember why nor can
    Brian> I imagine why - I will try it again and report back here
    Brian> with details of any errors encountered.

Unfortunately, I was right, I did have problems:

     type Byte_Array_Access is access all Byte_Array;
     pragma Convention (C,Byte_Array_Access);

produces:

serial.adb:107:11: warning: this access type does not correspond to C pointer

and:

   function To_LPCVOID is new 
      Ada.Unchecked_Conversion (Byte_Array_Access, Win32.LPCVOID);

produces:

serial.adb:144:04: warning: types for unchecked conversion have different sizes

So I tried:

   Type Char_Array_Ptr is access all Interfaces.c.Char_Array;
   pragma Convention (C,Char_Array_Ptr);

which produces:

serial.adb:89:09: warning: this access type does not correspond to C pointer

I still am not sure of the proper way of creating a C pointer in
Ada. So far I have see advice don't user 'Access and don't use
'Address as neither of these are portable. What is the correct way?

This is why my complicated solution was so complicated, I ended up:

1. Creating an aliased Byte_Array.
2. Creating a Interfaces.C.Strings.Char_Array_Access,
   copy access type using uchecked_conversion.
3. Converting to C pointer using Interfaces.C.Strings.To_Chars_Ptr.
4. Convert to LPCVOID using unchecked conversion.

Hmmm... I wonder if what I need is
system.address_to_access_conversions and/or
System.Storage_Elements.To_Integer?

However, all of this is complicated by the fact LPVOID and LPCVOID in
Ada is defined as a subtype of System.Address in the Windows bindings,
which implies the correct way to pass the parameter to
Item'Address. This is also the simplest way.

So I know people have said this is wrong, but I am going to assume if
the windows bindings use System.Address then this method will work on
Windows.
-- 
Brian May <bam@snoopy.apana.org.au>