<?phpif('ab'>'b'){echoa;}else{echob;}?>

结果为 b；

然后看代码 ：

<?phpfunctionkey_compare_func($key1,$key2){if($key1==$key2)return0;elseif($key1>$key2)return1;elsereturn-1;}$array1=array('blue'=>1,'red'=>2,'green'=>3,'purple'=>4);$array2=array('green'=>5,'blue'=>6,'yellow'=>7,'cyan'=>8);var_dump(array_diff_ukey($array1,$array2,'key_compare_func'));?>

结果：

array(2){["red"]=>int(2)["purple"]=>int(4)}

然后改动：

<?phpfunctionkey_compare_func($key1,$key2){if($key1==$key2)return1;elseif($key1>$key2)return0;elsereturn-1;}$array1=array('blue'=>1,'red'=>2,'green'=>3,'purple'=>4);$array2=array('green'=>5,'blue'=>6,'yellow'=>7,'cyan'=>8);var_dump(array_diff_ukey($array1,$array2,'key_compare_func'));?>

结果：

array(1){["blue"]=>int(1)}

很容易理解了