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From: Jeff Carter <carter@spam.innocon.com>
Subject: Re: Any research putting c above ada?
Date: 1997/05/07
Message-ID: <33709599.167EB0E7@spam.innocon.com>#1/1
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Organization: Innovative Concepts, Inc.
Newsgroups: comp.lang.ada
Date: 1997-05-07T00:00:00+00:00
List-Id: <comp.lang.ada>


Kevin Cline wrote:
> 
> amd001@its.maynick.com.au (Andrew Dunstan) wrote:
> 
> >The commonest errors (by far) that I have seen in
> >years of debugging other people's code (and some of my own) have been
> >pointer mismanagement and off-by-one errors in array processing. Ada
> >really does shine in helping you avoid these (as well as having many
> >other good points).
> 
> How does Ada help you avoid the problem of managing dynamically allocated
> memory?
Well, let's suppose you have a text file with N+1 lines, where N is not
known until run time. The 1st line is the string representation of an
integer (>= 0), N. The remaining N lines contain strings of varying
lengths.

In C, for example, I think you would have to read the value of N,
dynamically allocate an array of N pointers to char, then read each
string and dynamically allocate space for it pointed to by the
appropriate pointer in the array. You would also be responsible for
correctly deallocating this space when you are finished with it.

I don't have a great deal of C experience, so please pardon any errors I
have made. The important point is that this must involve explicit
allocation and deallocation.

In Ada (even Ada 83), no explicit allocation and deallocation is
required:

function Get_Line (File : Text_Io.File_Type) return String;

Text_Io.Create (File => File, ...

declare
   Image     : constant String  := Get_Line (File);
   Num_Lines : constant Natural := Natural'Value (Image);

   Line : array (1 .. Num_Lines) of Variable_String;
begin
   Read : for I in Line'range loop
      Line (I) := To_Variable_String (Get_Line (File) ):
   end loop Read;

   Text_Io.Close (File => File);

   -- use Line
end;

In Ada 83, you have to provide your own variable-length strings, which
would have to be bounded to provide automatic deallocation. In Ada, you
can use Ada.Strings.Bounded or Ada.Strings.Unbounded.
-- 
Jeff Carter  PGP:1024/440FBE21
Auntie-spam reply to; try ( carter @ innocon . com )
"Now go away, or I shall taunt you a second time."
Monty Python & the Holy Grail