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Re: AND statements [message #14498 is a reply to message #14494]

Mon, 01 March 1999 00:00

philaldis
Messages: 32
Registered: March 1999

Member

>> If you write some code like this:
>>
>> test=Ptr_New()
>>
>> IF Ptr_Valid(test) AND Size(*test, /type) NE 10 THEN print, *test
>>
>> ....can you always guarantee that it will not try to evaluate the second
>> statement if the first one was false - or is this a dangerous tactic to
>> adopt?
>
> Nope. In fact, I can guarantee that it *will* evaluate the whole
> logical expression. IDL is in this respect totally unlike C.
>
> If the urge is big enough, one could ask RSI nicely to implement
> operators like "AND THEN" and "OR ELSE" used like this:
>
> IF ptr_valid(test) AND THEN size(*test,/type) ne 10 then print,*test
>
> IF error_occurred OR ELSE check_for_error() then print,"Error"
>
> "AND THEN" works like C &&
> "OR ELSE" works like C ||, i.e. check_for_error() isn't called
> if "error_occurred" is already true.
>

> Stein Vidar

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
.
.
.
.
.
ENDIF

ENDIF

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

IF Ptr_Valid(ThisPointer) THEN BEGIN
IF Size(*ThisPointer, /type) EQ 10 THEN BEGIN
.
.
.
.
.
ENDIF ELSE flag = 1

ENDIF ELSE flag = 1

IF flag ........

While obviously this is not the end of the world, there could be more
complex examples, and the code does look messy.

Cheers,
Phil

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[Message index]

		Re: AND statements By: Steve Scheele on Fri, 05 March 1999 00:00
		Re: AND statements By: Steve Scheele on Wed, 03 March 1999 00:00
		Re: AND statements By: steinhh on Mon, 01 March 1999 00:00
		Re: AND statements By: philaldis on Mon, 01 March 1999 00:00
		Re: AND statements By: steinhh on Mon, 01 March 1999 00:00

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