| Re: AND statements [message #14494 is a reply to message #14451] |
Mon, 01 March 1999 00:00   |
steinhh
Messages: 260
Registered: June 1994
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Senior Member |
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In article <36da962e.18718769@146.80.9.44> philaldis@geocities.com
(Phil Aldis) writes:
> So, to avoid that you have to do some pretty messy code. Say for
> example I've got :
>
> IF Ptr_Valid(ThisPointer) THEN BEGIN
> IF Size(*ThisPointer, /type) EQ 10 THEN BEGIN
Yep, that's right. You do get used to it, though, even if you're
grown up with C style logical operators, taking advantage of the
non-evaluation of unnecessary parts for every little scrap of
efficiency improvement.
> However, I want to execute the same bit of code if it fails the
> Ptr_Valid and the Size(*ThisPointer, type0 EQ 10, so as far as I can
> see, (and I realise that I may be missing something pretty blatent),
> you have to use flags
[..snip..]
> While obviously this is not the end of the world, there could be more
> complex examples, and the code does look messy.
Yes, though you learn to rewrite those statements somewhat,
like this:
flag = NOT ptr_valid(thispointer)
IF NOT flag then flag = size(*thispointer,/type) EQ 10
IF NOT flag THEN BEGIN
;; Pointer is valid and points to type 10
END ELSE BEGIN
;; Pointer is not valid or doesn't point to type 10
END
There could be some improvement with the ?: construct:
flag = NOT (ptr_valid(thispointer) ? size(*thispointer,/type) eq 10 : 0b)
should be equivalent to the first two lines in my example.
In fact, you could rewrite your original code like this:
if (ptr_valid(ptr) ? size(*ptr,/type) eq 10 : 0b) then print,*ptr $
else flag=1b
I'm not sure whether *I* would use the ?: construct in cases like
this.... it looks more messy to me, in fact..
Regards,
Stein Vidar
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