On May 17, 2007, at 9:21 AM, Daniel Stenning wrote:
> fyi: 38 seconds vs 43 seconds.
>
> Not a lot but using a local var is still consistently faster.
>
>
> On 17/5/07 14:14, "Daniel Stenning" <d0stenning at msn dot com> wrote:
>
>>
>> Now I just did some timings, and it seems that there is a slight
>> ( not great
>> ) performance advantage with using a local variable.
>
> Regards,
The problem is that you're evaluating the ubound everytime you go
around the loop. The higher the ubound value the more times you'll
have to evaluate it and the slower your loop will run.
There is also a very slight penalty to declaring the variable inside
the loop, I just ran that test yesterday.
Anything you do more than once you need to be very careful about, any
slight overhead for a object lookup or a function call will add up
significantly the more you have to do it. If you only need to call
something once it doesn't really matter, but in a loop in can make a
huge difference in performance. Anything you repeatedly need to
compare against or use should be in a local variable and when
possible and when it makes sense for code readability you should not
redeclare any variables inside the loop.
dim i, count as integer
count = ubound( SomeArray)
for i = 0 to count
//do something
next
is always and without exception going to be faster than
for i as integer = 0 to ubound( SomeArray)
//
next
cause in the first example you're only calculating the ubound value
once. So get over thinking that the other is better, it uses fewer
lines of code, but is more complex and runs slower, so it's only an
illusion of betterness ;)
In addition object lookups and accesses are non-trivial so anything
else you can pull into a local variable for comparison helps a LOT too.
-James
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