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From: stephens@latcs1.oz.au (Philip J Stephens)
Newsgroups: comp.sys.apple2
Subject: Re: new() procedure in Pascal
Message-ID: <8744@latcs1.oz.au>
Date: 11 Sep 90 10:19:48 GMT
References: <5429.26ec0e29@vax5.cit.cornell.edu>
Distribution: comp
Organization: Comp Sci, La Trobe Uni, Australia
Lines: 45

Joel Sumner writes:
> One more Pascal related question.  When should I call the following?
> 
> var   p:pointer (or StringPtr, or anything pointer)
> begin
> ....
> new(p);
> ....
> end;
> 
> In other words, when do you have to call new()?

  A pointer variable is simply that: a two-byte variable
which contains an address to the actual data (thus the value
of p is an address, and the value of p^ is the data stored
at that address).
  Initially, p is not pointing to anything at all, hence
referencing p^ is likely to crash the program.  The
procedure new(p) allocates some memory to hold the data
(whose type is given in the var definition), and stores the
address of that data in p.

  The following program will thus allocate an integer
variable to the pointer p, store the value 10 in the integer
variable pointed to by p, then write that value out.

  var
    p: ^integer;

  begin
    new(p);
    p^ := 10;
    writeln(p^);
  end;

  I don't think you can use new(p) if p is of type pointer,
as you are not specifying what TYPE of data p must point to.
  I hope that helps.

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