Re: win32 interfacing check (SetClipboardData)

["Randy Brukardt" <randy@rrsoftware.com>]

> On 29/08/2017 22:28, Xavier Petit wrote:
>> Hi, I would like to know if this win32 code is "correct" from your PoV or 
>> could be written in a better way, especially this block :
>>
>> declare
>>  Tmp : Wide_String (1 .. Source'Length + 1) with Address => AMem;
>> begin
>>  Tmp := Source & Wide_Character'First;
>> end;
>
> It looks OK.

For me, using an address clause for anything other than interfacing to 
hardware is wrong. We certainly didn't do anything like this in Claw when 
implementing the clipboard operations. We used instances of 
Unchecked_Conversion to get a pointer of the right type, and then assigned 
into that. (Nowdays, I might use an instance of 
Address_to_Access_Conversions.)

The code that converts a String parameter into a value in the clipboard list 
looks like:

    procedure Append_Copy(Item : in     String;
                          List : in out Representation_List_Type;
                          Kind : in     Text_Kinds := Text) is
        use type Claw.Win32.HGlobal;
        Mem : Claw.Win32.HGlobal;
        subtype C_String_Type is Interfaces.C.Char_Array(0 .. Item'length);
        type Target_Pointer is access all C_String_Type;
        function Convert is new Ada.Unchecked_Conversion
          (Source => Claw.Win32.HGlobal,
           Target => Target_Pointer);
        N : Interfaces.C.Size_T;
    begin
        Mem := Claw.Low_Level.Miscellaneous.Global_Alloc (
          Claw.Low_Level.Miscellaneous.GMEM_FIXED,
          DWord(C_String_Type'Length*(Interfaces.C.Char'Size/8)));
        if Mem = Claw.Win32.NULL_HGLOBAL then
            Claw.Raise_Windows_Error;
        end if;
        Interfaces.C.To_C(Item, Convert(Mem).all, N);
        Append((Handle => Mem, Format => Text_Kind_Format(Kind),
                Delayed_Renderer => null), List);
    end Append_Copy;

"Append" here adds "Mem" to the Representation_List, giving ownership of the 
handle to the List.

A Wide_String version would work the same way, using the appropriate 
Interfaces.C types.

Note that we were trying for maximum portability (to any sane Ada 95 
compiler for Windows); there's no real need to use the Interfaces.C types on 
GNAT (if that's all you care about).

                              Randy.