php - PHP 中的数组引用混淆

Question

$arr = array(1);
$a = & $arr[0];

$arr2 = $arr;
$arr2[0]++;

echo $arr[0],$arr2[0];

// Output 2,2

你能帮我看看怎么可能吗？

Answer 1

Note, however, that references inside arrays are potentially dangerous. Doing a normal (not by reference) assignment with a reference on the right side does not turn the left side into a reference, but references inside arrays are preserved in these normal assignments. This also applies to function calls where the array is passed by value.

/* Assignment of array variables */
$arr = array(1);
$a =& $arr[0]; //$a and $arr[0] are in the same reference set
$arr2 = $arr; //not an assignment-by-reference!
$arr2[0]++;
/* $a == 2, $arr == array(2) */
/* The contents of $arr are changed even though it's not a reference! */