phpの一部の機能を詳しく解説

<?php
$a1=array("2"=>"this_2","3"=>"this_3","4"=>"this_4","5"=>"this_5");
$a2=array("1"=>"this_1","2"=>"this_2","3"=>"this_3");

$result1 = array_diff_assoc($a1,$a2); //数组可以交换顺序滴，也可以是多个数组
var_dump($result1);
?>

array (size=2)
  4 => string 'this_4' (length=6)
  5 => string 'this_5' (length=6)

<?php
$a1=array("2"=>"this_2","3"=>"this_3","4"=>"this_4","5"=>"this_5");

$result2 = array_keys($a1);
var_dump($result2);
?>

array (size=4)
  0 => int 2
  1 => int 3
  2 => int 4
  3 => int 5

<?php
$a1=array("2"=>"this_2","3"=>"this_3","4"=>"this_4","5"=>"this_5");

if (key_exists("2",$a1)){
	echo "yes!";
}else{
	echo "no!";
}
?>

yes!

<?php
$a1=array("2"=>"this_2","3"=>"this_3","4"=>"this_4","5"=>"this_5");

$result3 = count($a1);
echo $result3;
?>

4