[KLUG Members] PHP vs ASP

[Buist Justin]

In most languages a multi-part conditional will only evaluate as much as it needs to to determine if the entire expression will be true.  For instance, in C:

if (func_a() || func_b()) {
	/* stuff */
}

if func_a() returns true func_b() will never be run, because it's an 'or' statement it doesn't matter what the result of func_b() is if func_a() is true.  Another example:

if (a != NULL && memcpy(a, b, 1024) > 0) {
	/* do stuff */
}

With most languages, if 'a' is NULL the memcpy() would never run.  However, with a non-short-circuiting language the memcpy() will always run, which means to be safe you'd have to use:
if (a != NULL) {
	if (memcpy(a, b, 1024) > 0) {
		/* do stuff */
	}
}

It doesn't seem like such a big deal at first, until you've grown accustomed to short-circuit logic and depend on it.  Looping on multiple conditions can become a real pain too.

FYI:  ColdFusion (at least prior to MX -- I haven't used that yet) is another web scripting language that won't short-circuit, making for some pretty ugly code.

Justin Buist



> -----Original Message-----
> From: Peter Buxton [mailto:peter@killdevil.org]
> Sent: Tuesday, November 12, 2002 10:43 PM
> To: members@kalamazoolinux.org
> Subject: Re: [KLUG Members] PHP vs ASP
> 
> 
> On Mon, Nov 11, 2002 at 03:00:18PM -0500, Buist Justin wrote:
> 
> > c)  Short-circuited conditionals.
> > This is a major pet-peeve of mine.  Vbscript won't short-circuit a
> > conditional which prevents me from writing stuff like:
> > 
> > Do Until (rs.EOF() AND rs.Fields("ProductID").Value <> 
> lngLastProductID )
> > 	' ... stuff
> > Loop
> 
> Ummm... short circuit a conditional???
> 
> -- 
> for gpg key: http://killdevil.org/~peter
> [The Basement Tapes were] like the Watergate tapes... Bob
> would say, 'We should destroy this.' -- Robbie Robertson
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