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Date: 26 Aug 93 14:09:09 GMT
From: psinntp!psinntp!jupiter.fuentez.com!hildjj@uunet.uu.net  (Joe Hildebrand)
Subject: Re: How to assign STRINGs?
Message-ID: <HILDJJ.93Aug26100909@jupiter.fuentez.com>
List-Id: <comp.lang.ada>

>> On 25 Aug 93 21:42:26 GMT, alex@cs.umd.edu (Alex Blakemore) said:
In article <25gmc2$3cf@neomimsy.cs.umd.edu> alex@cs.umd.edu (Alex Blakemore) wr
ites:


   Alex> In article <1993Aug25.121754.20413@hellgate.utah.edu>
   Alex> matwood%peruvian.cs.utah.edu@cs.utah.edu (Mark Atwood)
   Alex> writes:
   >> how DO i assign the results of a function returning an
   >> unconstrained string to a constrained string?

   Alex> in Ada83, you have two good choices (and one sort of kludgy
   Alex> one)

   Alex> a. initialize a constant string with the function result
   Alex> cmdline : constant string := dos.get_parms;

   Alex> b. pass the function result as an in parameter to another
   Alex> subprogram text_io.put_line (dos.get_parms);

   Alex> or [worst of all]

   Alex> c. get the bounds first, declare the variable, call the
   Alex> function

   Alex> declare cmdline : string (dos.first_parm_number
   Alex> .. dos.last_parm_number); begin cmdline := dos.get_parms;
   Alex> end;

   Alex> -- this is brittle, esp if you ever add concurrency

We created a simple function that combines b. and c.


NOTE: I don't claim this is pretty, but it seems to work.  It needs
some cleaning up, since this is one one the first functions we wrote
when we were learning Ada.  In particular, Out_Str should only be an
out parameter.  PAR_STR_Length returns the number of "useful"
characters in a string by subtracting the number of trailing spaces
and ascii.nul's.


procedure PAR_STR_copy( Out_str   : in out string;
                        In_Str    : in     string;
                        Pad_Char  : in     character := ' ' ) is 

     In_str_len	 : integer := 0;
     Out_str_len : integer := 0;
     Low_Char    : integer := 0;
     Num_Chars   : integer := 0;

begin

--	Get the length of the string to be copied

   In_Str_Len := PAR_STR_length( In_Str );

--	Obtain the size of the target string

   Out_Str_Len := Out_Str'last - Out_Str'first + 1;

--	Find the first character position in the In_Str to be copied.
--	This is in case the In_Str is passed in as a string slice.

   Low_Char := In_Str'first;

--	Only copy In_Str_Len number of characters

   Num_Chars := In_Str_Len;

--	Make sure we only copy the number of characters the target
--	string can hold.

   if ( Num_Chars > Out_Str_Len ) then
      Num_Chars := Out_Str_Len;
   end if;

--	Copy the string.

   Out_Str( Out_Str'first..(Out_Str'first+Num_Chars-1)) := 
                             In_Str(Low_Char..(Low_Char+Num_Chars-1));

--	Pad out the remaining cells with the pad character.

Pad_LOOP:
   for i in (Out_Str'first+Num_Chars)..Out_Str'last loop
     Out_Str(i) := Pad_Char;
   end loop Pad_LOOP;

end PAR_STR_copy;


--

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