Put_Line for chars_ptr

Put_Line for chars_ptr

[Adrian Knoth]

Hi!

I have a record (struct) for interfacing uname(). The record looks like

type myStruct is record
  sysname : chars_ptr;
  nodename: chars_ptr;
  release : chars_ptr;
  version : chars_ptr;
  machine : chars_ptr;
end record;

I guess Pragma Import works well, but if I try to output the content
via Value(varname.sysname) & ... &... it cannot handle a null-pointer
(raise Dereference-Error).

Is this the wrong approach?

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Re: Put_Line for chars_ptr

[tmoran]

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

Re: Put_Line for chars_ptr

[Adrian Knoth]

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.

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Re: Put_Line for chars_ptr

[Sergey Koshcheyev]

"Adrian Knoth" <adi@drcomp.erfurt.thur.de> wrote in message
news:slrnaha10h.102.adi@drcomp.erfurt.thur.de...
> Hi!
>
> I have a record (struct) for interfacing uname(). The record looks like
>
> type myStruct is record
>   sysname : chars_ptr;
>   nodename: chars_ptr;
>   release : chars_ptr;
>   version : chars_ptr;
>   machine : chars_ptr;
> end record;

I've just looked at the uname man page, and the structure looks like this:
struct utsname {
    char sysname[SYS_NMLN];
    char nodename[SYS_NMLN];
    char release[SYS_NMLN];
    char version[SYS_NMLN];
    char machine[SYS_NMLN];
    char domainname[SYS_NMLN];
};
There aren't pointers there, but the arrays themselves. So you should
declare your Ada structure as
type utsname is record
    sysname : char_array (1 .. SYS_NMLN);
    ...
end record;
Sergey.

Re: Put_Line for chars_ptr

[Adrian Knoth]

Sergey Koshcheyev <serko84@hotmail.com> wrote:

>> I have a record (struct) for interfacing uname(). The record looks like
>> type myStruct is record
>>   sysname : chars_ptr;
> I've just looked at the uname man page, and the structure looks like this:
> struct utsname {
>     char sysname[SYS_NMLN];

Oh, thanks a lot. My info-page seems to be wrong on this, they call it
an unbounded char-array, that's why I thought they provide a pointer to
the first character and do the usual stuff like null-terminated strings.

>     sysname : char_array (1 .. SYS_NMLN);

It works fine now, thanks.

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

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