comp.lang.idl-pvwave archive: archive

Home » Public Forums » archive » Re: Oh No...

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Oh No... [message #53501 is a reply to message #53500]

Wed, 18 April 2007 06:04

Foldy Lajos
Messages: 268
Registered: October 2001

Senior Member

On Wed, 18 Apr 2007, Paolo Grigis wrote:

>
> Speaking of which, what about
>
> IDL> delvar,a ;undefines a
> IDL> a[(a=2*findgen(10))]=1 ;agreed, this is a bit crazy, but hold on
> IDL> print,a
> 1.00000 1.00000 1.00000 6.00000 8.00000
> 10.0000 1.00000
> 14.0000 1.00000 1.00000
>
> Now, this must be a bug, surely... (or a very strange feature indeed).
>

No, invalid code, with undefined result :-)

We have no formal definition of the IDL syntax, but there is a rule in
Fortran/C/C++/... which should be true for IDL, too: a memory cell can
be modified at most once in an expression. You are modifying 'a' twice
in a single expression.

(Section 6.5#2 of the C99 specification: "Between the previous and next
sequence point an object shall have its stored value modified at most once
by the evaluation of an expression. Furthermore, the prior value shall be
accessed only to determine the value to be stored.")

regards,
lajos

Report message to a moderator

[Message index]

		Re: Oh No... By: Paolo Grigis on Wed, 18 April 2007 06:45
		Re: Oh No... By: Foldy Lajos on Wed, 18 April 2007 06:04
		Re: Oh No... By: Paolo Grigis on Wed, 18 April 2007 05:38
		Re: Oh No... By: Michael Galloy on Wed, 18 April 2007 11:01

Previous Topic:	Text in plots
Next Topic:	Oh No...

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sat Oct 11 09:06:29 PDT 2025

Total time taken to generate the page: 0.00675 seconds