First of all, I understand in 90% of applications the performance difference is completely irrelevant, but I just need to know which is the faster construct. That and...
The information currently available on them on the net is confusing. A lot of people say foreach is bad, but technically it should be faster since it's suppose to simplify writing a array traversal using iterators. Iterators, which are again suppose to be faster, but in PHP are also apparently dead slow (or is this not a PHP thing?). I'm talking about the array functions: next() prev() reset() etc. well, if they are even functions and not one of those PHP language features that look like functions.
To narrow this down a little: I'm not interesting in traversing arrays in steps of anything more than 1 (no negative steps either, ie. reverse iteration). I'm also not interested in a traversal to and from arbitrary points, just 0 to length. I also don't see manipulating arrays with more than 1000 keys happening on a regular basis, but I do see a array being traversed multiple times in the logic of a application! Also as for operations, largely only string manipulation and echo'ing.
Here are few reference sites:
http://www.phpbench.com/
http://www.php.lt/benchmark/phpbench.php
What I hear everywhere:
foreach is slow, and thus for/while is fasterforeach copies the array it iterates over; to make it faster you need to use references$key = array_keys($aHash); $size = sizeOf($key);
for ($i=0; $i < $size; $i++) is faster than a foreachHere's my problem. I wrote this test script: http://pastebin.com/1ZgK07US and no matter how many times I run the script, I get something like this:
foreach 1.1438131332397
foreach (using reference) 1.2919359207153
for 1.4262869358063
foreach (hash table) 1.5696921348572
for (hash table) 2.4778981208801
In short:
foreach is faster than foreach with referenceforeach is faster than forforeach is faster than for for a hash tableCan someone explain?
PHP Version 5.3.0
Thank you everyone who tried to help.
I'll likely stick to foreach (the non-reference version) for any simple traversal.
This question is related to
php
arrays
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foreach
for-loop
I'm not sure this is so surprising. Most people who code in PHP are not well versed in what PHP is actually doing at the bare metal. I'll state a few things, which will be true most of the time:
If you're not modifying the variable, by-value is faster in PHP. This is because it's reference counted anyway and by-value gives it less to do. It knows the second you modify that ZVAL (PHP's internal data structure for most types), it will have to break it off in a straightforward way (copy it and forget about the other ZVAL). But you never modify it, so it doesn't matter. References make that more complicated with more bookkeeping it has to do to know what to do when you modify the variable. So if you're read-only, paradoxically it's better not the point that out with the &. I know, it's counter intuitive, but it's also true.
Foreach isn't slow. And for simple iteration, the condition it's testing against — "am I at the end of this array" — is done using native code, not PHP opcodes. Even if it's APC cached opcodes, it's still slower than a bunch of native operations done at the bare metal.
Using a for loop "for ($i=0; $i < count($x); $i++) is slow because of the count(), and the lack of PHP's ability (or really any interpreted language) to evaluate at parse time whether anything modifies the array. This prevents it from evaluating the count once.
But even once you fix it with "$c=count($x); for ($i=0; $i<$c; $i++) the $i<$c is a bunch of Zend opcodes at best, as is the $i++. In the course of 100000 iterations, this can matter. Foreach knows at the native level what to do. No PHP opcodes needed to test the "am I at the end of this array" condition.
What about the old school "while(list(" stuff? Well, using each(), current(), etc. are all going to involve at least 1 function call, which isn't slow, but not free. Yes, those are PHP opcodes again! So while + list + each has its costs as well.
For these reasons foreach is understandably the best option for simple iteration.
And don't forget, it's also the easiest to read, so it's win-win.
I think but I am not sure : the for loop takes two operations for checking and incrementing values. foreach loads the data in memory then it will iterate every values.
It's 2020 and stuffs had greatly evolved with php 7.4 and opcache.
Here is the OP^ benchmark, ran as unix CLI, without the echo and html parts.
Test ran locally on a regular computer.
php -v
PHP 7.4.6 (cli) (built: May 14 2020 10:02:44) ( NTS )
Modified benchmark script:
<?php
## preperations; just a simple environment state
$test_iterations = 100;
$test_arr_size = 1000;
// a shared function that makes use of the loop; this should
// ensure no funny business is happening to fool the test
function test($input)
{
//echo '<!-- '.trim($input).' -->';
}
// for each test we create a array this should avoid any of the
// arrays internal representation or optimizations from getting
// in the way.
// normal array
$test_arr1 = array();
$test_arr2 = array();
$test_arr3 = array();
// hash tables
$test_arr4 = array();
$test_arr5 = array();
for ($i = 0; $i < $test_arr_size; ++$i)
{
mt_srand();
$hash = md5(mt_rand());
$key = substr($hash, 0, 5).$i;
$test_arr1[$i] = $test_arr2[$i] = $test_arr3[$i] = $test_arr4[$key] = $test_arr5[$key]
= $hash;
}
## foreach
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr1 as $k => $v)
{
test($v);
}
}
echo 'foreach '.(microtime(true) - $start)."\n";
## foreach (using reference)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr2 as &$value)
{
test($value);
}
}
echo 'foreach (using reference) '.(microtime(true) - $start)."\n";
## for
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
$size = count($test_arr3);
for ($i = 0; $i < $size; ++$i)
{
test($test_arr3[$i]);
}
}
echo 'for '.(microtime(true) - $start)."\n";
## foreach (hash table)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
foreach ($test_arr4 as $k => $v)
{
test($v);
}
}
echo 'foreach (hash table) '.(microtime(true) - $start)."\n";
## for (hash table)
$start = microtime(true);
for ($j = 0; $j < $test_iterations; ++$j)
{
$keys = array_keys($test_arr5);
$size = sizeOf($test_arr5);
for ($i = 0; $i < $size; ++$i)
{
test($test_arr5[$keys[$i]]);
}
}
echo 'for (hash table) '.(microtime(true) - $start)."\n";
Output:
foreach 0.0032877922058105
foreach (using reference) 0.0029420852661133
for 0.0025191307067871
foreach (hash table) 0.0035080909729004
for (hash table) 0.0061779022216797
As you can see the evolution is insane, about 560 time faster than reported in 2012.
On my machines and servers, following my numerous experiments, basics for loops are the fastest. This is even clearer using nested loops ($i $j $k..)
It is also the most flexible in usage, and has a better readability from my view.
One thing to watch out for in benchmarks (especially phpbench.com), is even though the numbers are sound, the tests are not. Alot of the tests on phpbench.com are doing things at are trivial and abuse PHP's ability to cache array lookups to skew benchmarks or in the case of iterating over an array doesn't actually test it in real world cases (no one writes empty for loops). I've done my own benchmarks that I've found are fairly reflective of the real world results and they always show the language's native iterating syntax foreach coming out on top (surprise, surprise).
//make a nicely random array
$aHash1 = range( 0, 999999 );
$aHash2 = range( 0, 999999 );
shuffle( $aHash1 );
shuffle( $aHash2 );
$aHash = array_combine( $aHash1, $aHash2 );
$start1 = microtime(true);
foreach($aHash as $key=>$val) $aHash[$key]++;
$end1 = microtime(true);
$start2 = microtime(true);
while(list($key) = each($aHash)) $aHash[$key]++;
$end2 = microtime(true);
$start3 = microtime(true);
$key = array_keys($aHash);
$size = sizeOf($key);
for ($i=0; $i<$size; $i++) $aHash[$key[$i]]++;
$end3 = microtime(true);
$start4 = microtime(true);
foreach($aHash as &$val) $val++;
$end4 = microtime(true);
echo "foreach ".($end1 - $start1)."\n"; //foreach 0.947947025299
echo "while ".($end2 - $start2)."\n"; //while 0.847212076187
echo "for ".($end3 - $start3)."\n"; //for 0.439476966858
echo "foreach ref ".($end4 - $start4)."\n"; //foreach ref 0.0886030197144
//For these tests we MUST do an array lookup,
//since that is normally the *point* of iteration
//i'm also calling noop on it so that PHP doesn't
//optimize out the loopup.
function noop( $value ) {}
//Create an array of increasing indexes, w/ random values
$bHash = range( 0, 999999 );
shuffle( $bHash );
$bstart1 = microtime(true);
for($i = 0; $i < 1000000; ++$i) noop( $bHash[$i] );
$bend1 = microtime(true);
$bstart2 = microtime(true);
$i = 0; while($i < 1000000) { noop( $bHash[$i] ); ++$i; }
$bend2 = microtime(true);
$bstart3 = microtime(true);
foreach( $bHash as $value ) { noop( $value ); }
$bend3 = microtime(true);
echo "for ".($bend1 - $bstart1)."\n"; //for 0.397135972977
echo "while ".($bend2 - $bstart2)."\n"; //while 0.364789962769
echo "foreach ".($bend3 - $bstart3)."\n"; //foreach 0.346374034882
Source: Stackoverflow.com