在for语句中计算一个数组大小的更好方法是哪种？

Question

Which is faster? are there reasons to use one over the other?
for($i = 0; $i < count($array); ++$i){ ... }
OR
for($i = 0, $size = count($array); $i < $size; ++$i){ ... }

http://php.net/manual/en/control-structures.for.php states: "The above code can be slow, because the array size is fetched on every iteration. Since the size never changes, the loop be easily optimized by using an intermediate variable to store the size instead of repeatedly calling count():"

Is the interpreter actually that dumb?

Answer 1

In this case in each iteration you must call the function count() , the time complexity is O(n) :

for($i = 0; $i < count($array); ++$i){ ... }

In this case you call once count() at te begining, and you use the store value of $size , time complexity is O(1) . This case is more faster:

for($i = 0, $size = count($array); $i < $size; ++$i){ ... }