array_diff_assoc文档代码的意外结果

Question

Here is an example from PHP documentation about array_diff_assoc.

In this example you see the "a" => "green" pair is present in both arrays and thus it is not in the output from the function. Unlike this, the pair 0 => "red" is in the output because in the second argument "red" has key which is 1.

<?php
$array1 = array("a" => "green", "b" => "brown", "c" => "blue", "red");
$array2 = array("a" => "green", "yellow", "red");
$result = array_diff_assoc($array1, $array2);
print_r($result);
?>

The above example will output:

Array
(
    [b] => brown
    [c] => blue
    [0] => red
)

red is present in both arrays, but it is returned in the output of array_diff_assoc, why PHP think that red in $array1 and $array2 is different?

Answer 1

That is because in the first array the index of red is 0 and in the second array the index of red is 1 so they are different.

array_diff_assoc

From the docs:

Computes the difference of arrays with additional index check

Check the vardumps:

<?php

$array1 = array("a" => "green", "b" => "brown", "c" => "blue", "red");
$array2 = array("a" => "green", "yellow", "red");
var_dump($array1);
var_dump($array2);

Output:

array(4) {
  ["a"]=>
  string(5) "green"
  ["b"]=>
  string(5) "brown"
  ["c"]=>
  string(4) "blue"
  [0]=>
  string(3) "red"
}
array(3) {
  ["a"]=>
  string(5) "green"
  [0]=>
  string(6) "yellow"
  [1]=>
  string(3) "red"
}