Question

$array='hello hello2';
foreach(explode(' ',$array) as $v)
 echo $v;

How many times does explode get executed?

And is it better that to use another var like:

   $exploded = explode(...);
   foreach($exploded as $v)
      ...

?

Answer 1

It only gets executed once. foreach will operate on a copy of the return value of explode (array or false).

foreach is a language construct which expects $array as $key => $value. $array can be any expression which evaluates to an array, and explode is such a function. The expression is evaluated only once, and then foreach operates on the result of the expression.

This is different with a regular for loop for instance. A for loop takes three expressions. Both the second and third expression are evaluated for each iteration of the loop.

So with a for loop there could be a difference (leaving optimization and the O(1)-performance of count aside) between these two statements:

for($i = 0; $i < count($array); ++$i) { … }
// vs.
for($i = 0, $c = count($array); $i < $c; ++$i) { … }