Using fwrite in Ada

["Makhno" <root@127.0.0.1>]

Hello,
I want to read and write binary data from stdin/stdout, unfortunately Ada's
usual IO routines appear to be text only and (on Win32) convert code 10 to
codes 10 & 13.
To get round this I'm trying to use Interfaces.C_Streams, but I don't know
enough Ada to get them working.
How to I get a String into the fwrite function?
I tried

procedure MainCode is

 cptr : chars_ptr;
 Buffer : String (1..100);
 vptr : voids;

 begin

-- fill Buffer with binary data here

  cptr:=New_String(Buffer);
  vptr:=voids(cptr);

  fwrite(vptr,100,1,stdout);
 end;

But this won't compile, the compiler says that it cannot convert the
chars_ptr to voids. Coming from a C background, I don't understand why
something cannot be cast to void.

Does anybody have any idea as to how I get binary data onto stdout?

Thanks