Re: :( This fact ruins my understanding of php :( please explain!

Thanks for ur interest. Seairth Jacobs <seairth@seairth.com> wrote in message news:20021009015338.4579.qmail@pb1.pair.com... > I have a couple thoughts... > > 1) In some other languages, passing an array by value only passes the first > element value, not the whole array. This may be happening here, which would > explay the fast execution times. I don't know this for sure, but it could > easily be tested by seeing what's in $a inside the function f(). > > 2) Try returning the array by reference... > > function &f(&$a){return $a;} > > for ($i=0; $i < 100; $i++){$a = & f($big);} > > --- > Seairth Jacobs > seairth@seairth.com > > > "Markas" <mark@e-net.lt> wrote in message > news:20021008234646.41097.qmail@pb1.pair.com... > > I tried some trivial expirements: > > > > /* here I define an array $big, which I guess would "eat" ~100kb of memory > > */ > > for($i=0; $i<10000; $i++) > > { > > $big[$i] = "1234567890"; > > } > > > > /* this func only returns the value it gets as a param...*/ > > function f($a){return $a;} > > > > $start = microtime(); > > > > /* here all the job is done */ > > for ($i=0; $i < 100; $i++){$a = f($big);} /* <--- every iteration I just > > pass $big array to this func and it simply returns it*/ > > > > $end = microtime(); > > > > /* here I find out the time the job above takes to run, similar to the > code > > from the help:*/ > > function > > microtime($time){ > > list($usec, $sec) = explode(" ",$time); > > return ((float)$usec + (float)$sec); > > } > > > > $time_start = getmicrotime($start); > > $time_end = getmicrotime($end); > > $time = $time_end - $time_start; > > > > echo "Did nothing in $time seconds"; > > > > So the script above takes on my server ~0.00115 sec, so as far as I > understand, it takes php to copy that $big array which is rather large, at > least 100 times... So I decided to change the function f($a): > > function f($a){return $a;} changed to function f(&$a){return $a;}, > > as you can see, I only wanted to pass that $a param by reference, without > copying it, so I thought I win in performance and the 100 iterations will > work faster, as no copying of such a large array $big (which is this time > going to be passed by refernce) will be involved,... BUT this case the job > took ~3.75093 seconds, which is 3262 times SLOWER !!! I also found out, > that while using refernces, the time of job's run strictly depends on the > $big array dimension, and while NOT using references, the time doesn't > depend on that, but I thought just on the contrary. I thought, that while > using references, we dont copy the data and therefore do not depend on that > data amount, but the example above shows just the opposite results... > > > > What's going on, if anybody gets interested, please explain? > > > > > > > > > > > > > > > >