From: Wei Jen Yeh
Subject: portable O(1) strlen
Date: Thu, 13 Aug 1992 07:23:45 +0000
Message-ID: <19247@ector.cs.purdue.edu>

Hello,
  I just found a bug in my program caused by thinking that
	(array-dimension (format NIL "1234") 0) = 4.
Strange thing is that the answer is correct if I call string-downcase
on the value that format returns.  I can understand why they behave so.
But are there some related rules on this matter? I checked Cltl I, but could
not find discussions on strlen in the string section.  A quick solution that
I'm using now is to (1) scan the array, (2) coerce it to list then call
length, or (3) write a C function.  Solution (1) doesn't seem safe, since
I cannot be sure that the strings will be padded with some fixed chars.
(2) is O(n), and (3) is not portable.

So, is there a portable O(1) STRLEN?

Thanks.
Wei Jen Yeh                      ···@cs.purdue.edu
                                 Department of Computer Science
                                 Purdue University
                                 West Lafayette, Indiana

• Re: portable O(1) strlen Wei Jen Yeh
• Re: portable O(1) strlen Barry Margolin

From: Wei Jen Yeh
Subject: Re: portable O(1) strlen
Date: Thu, 13 Aug 1992 07:50:02 +0000
Message-ID: <19248@ector.cs.purdue.edu>

In article <·····@ector.cs.purdue.edu>, I wrote...
> Hello,
>   I just found a bug in my program caused by thinking that
> 	(array-dimension (format NIL "1234") 0) = 4.
> ...
> 
> So, is there a portable O(1) STRLEN?
> 

Thanks. I found the answer --- LENGTH.

Wei Jen Yeh                      ···@cs.purdue.edu
                                 Department of Computer Science
                                 Purdue University
                                 West Lafayette, Indiana

From: Barry Margolin
Subject: Re: portable O(1) strlen
Date: Thu, 13 Aug 1992 09:18:05 +0000
Message-ID: <16d9cdINNmde@early-bird.think.com>

In article <·····@ector.cs.purdue.edu> ···@cs.purdue.EDU (Wei Jen Yeh) writes:
>Hello,
>  I just found a bug in my program caused by thinking that
>	(array-dimension (format NIL "1234") 0) = 4.

Is FORMAT returning a longer string with a fill pointer?  I thought that
functions that create strings were supposed to return simple strings.  What
Lisp does this?

>So, is there a portable O(1) STRLEN?

LENGTH is O(1) when the argument is a vector, although the coefficient will
usually be higher than ARRAY-DIMENSION, since it has to check whether the
argument is a vector or list, and whether it has a fill pointer.
-- 
Barry Margolin
System Manager, Thinking Machines Corp.

······@think.com          {uunet,harvard}!think!barmar