Path: utzoo!attcan!uunet!samsung!usc!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Would like to emulate an array of pointers to a structure
Message-ID: <7577@jpl-devvax.JPL.NASA.GOV>
Date: 28 Mar 90 17:52:57 GMT
References: <12170003@hpccc.HP.COM>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 46

In article <12170003@hpccc.HP.COM> okamoto@hpccc.HP.COM (Jeff Okamoto) writes:
: I'm trying to do some manipulations on the password file.  What I'd like
: to be able to do is to somehow be able to reference one entire line of
: it with a single index value.  I know I can do this with an array of
: entire password file lines, but I don't want to keep having to split
: each line while searching for a particular entry (e.g., login name).

Whenever you find yourself saying things like "searching for a particular
entry", it probably means you should invert the database with one or more
associative arrays.

: The C equivalent would be an array of pointers to a structure.  Is
: there an easy (and intuitive!) method for doing what I'm trying to do?

If you want to program in C, program in C.  It's a nice language.  I use
it occasionally...   :-)

The closest thing would be parallel arrays, but again, that's probably not what
you wanna do.  You could generate an array of arrays using the * notation:

	$sym = 'X000';
	$i = 0;
	while (<PASSWD>) {
	    chop;
	    $pw[$i++] = *entry = $sym++;
	    @entry = split(/:/);
	}

	# later...

	*entry = $pw[$somenum];
	if (@entry[0] == $login) { ...

But it's probably more "intuitive" to split each time.  Split on a single
character is fairly efficient.

But don't do it that way.  Use associative arrays.  Or just search with
a pattern on the whole line--Perl will do it very efficiently if there
are any constant strings in the pattern.

Perl isn't about nested data structures.  It prefers flat data structures.
Perl is more like a chainsaw than a jig saw.  Or think of Perl as a bigger
hammer.  It lets you treat everything like a nail, and get away with it most
of the time.  But sometimes not.

Larry