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From: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Newsgroups: comp.lang.ada
Subject: Re: Put_Line for chars_ptr
Date: 23 Jun 2002 09:20:06 GMT
Organization: Modern Electronics
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Date: 2002-06-23T09:20:06+00:00
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tmoran@acm.org <tmoran@acm.org> wrote:

>> via Value(varname.sysname) & ... &... it cannot handle a null-pointer
>> (raise Dereference-Error).
>   What else should Value(null pointer) do?  

But there is no null pointer. It only complains about it, the record is
filled out.

> How about using something like:
> function S(Item : in chars_ptr) return String is
> begin
>   if Item = Null_Ptr then return "?";
>   else return Value(Item);
> end S;

This is exactly the code Interfaces.C.Strings uses:

   function Value (Item : in chars_ptr) return char_array is
      Result : char_array (0 .. Strlen (Item));

   begin
      if Item = Null_Ptr then
         raise Dereference_Error;
      end if;

      --  Note that the following loop will also copy the terminating Nul

      for J in Result'Range loop
         Result (J) := Peek (Item + J);
      end loop;

      return Result;
   end Value;

(it first generates char_array from chars_ptr and then converts this array
via To_Ada to an ordinary string:

   function Value (Item : in chars_ptr) return String is
   begin
      return To_Ada (Value (Item));
   end Value;

I think this is what I want to do, but it fails. Sometimes with storage_error.

-- 
mail: adi@thur.de  	http://adi.thur.de	PGP: v2-key via keyserver

Never underestimate the power of a small tactical nuclear weapon.