Re: Converting pointers to non nul-terminated C "strings" to Ada string

[likai3g@gmail.com]

On 2月14日, 下午2时58分, xorquew...@googlemail.com wrote:
> Hello.
>
> I have some C code that returns a pointer to a buffer of
> "data" (not a string, just raw data) and also returns the
> size of the buffer:
>
> void
> get_data (char **ptr, int *size);
>
> int size;
> char *ptr;
>
> get_data (&ptr, &size);
>
> The code is part of a library that I don't control, so I can't
> change the interface.
>
> I've defined the Ada equivalent as:
>
>     package CS renames Interfaces.C.Strings;
>     package C renames Interfaces.C;
>
>     procedure memory_data
>       (data   : out CS.chars_ptr;
>        size   : out C.int);
>     pragma Import (C, memory_data, "get_data");
>
> This works correctly, however I'm having trouble converting
> the chars_ptr type to an Ada string given that it's not nul-
> terminated.
>
> Attempts to do the following:
>
> return CS.Value (Item => data, Length => size);
>
> ... results in a String as long as the position of the first nul in
> the
> C string (the position is inevitably less than the length of the
> string).
>
> Is it possible to properly convert unterminated C strings or do I
> need to start messing about with raw System.Address types?
--try this....
   declare
      subtype Huge is String(Positive);
      type PHuge is access all Huge;
      type CString is record
	 Data: PHuge;
	 Size: Natural;
      end record;
      pragma Convention(C_Pass_By_Copy, CString);
      procedure Get_Data(S: out CString);
      pragma Import(C, Get_Data, "get_data");
      S: CString;
   begin
      Get_Data(S);
      Ada.Text_IO.Put_Line(S.Data(1..S.Size));
   end;