array issues when using ajax - php

Question

I am trying to use ajax to compare two arrays to see if a particular value set is the same or not, so I filled both arrays with the same values and when i tested them my test says that they are not the same. The first array was made on fileA.php (with a while loop pulling directly from a database)and uses ajax to send it as a url variable to fileB.php (the responding file). On fileB.php I then use a $_GET to get the array , and create another array with a while loop pulling the exact same values directly from the database and compare the two . At this point the two arrays should be the same, but as I said earlier my test says they aren't .So I did a var_dump of both arrays and they looked different for some reason.
first array dump:
array(2) {
[0]=>
array(0) {
}
[1]=>
string(6) ",2,2,1"
}
second array dump:
array(3) {
[0]=>
array(0) {
}
[1]=>
string(1) "2"
[2]=>
string(1) "2"
[3]=>
string(1) "1"
}
array 1 is made on fileA.php
while ($row = mysql_fetch_assoc($res))
{
$iState[] = $row["state"];
}///end while
then i use ajax to send to fileB.php
js_array=<? echo json_encode($iState); ?>;
var url_js_array=js_array.join(',');
xmlhttp.open("GET","fileB.php?istate="+ url_js_array,true);
xmlhttp.send();
then in fileB.php(ajax response file) i retrieve the array
$iStateValues[] =$_GET["istate"] ;
then I create array 2 on fileB.php
while ($row = mysql_fetch_array($res))
{
$currentiState[]= $row["state"];
}///end while
then I compred the two
echo"\n\nsame test\n";
if($iStateValues==$currentiState)
echo "same";
else
echo "not same";
The var_dumps of the two arrays are different but they were created the exact same way . Wh is this?????

Answer 1

Your arrays are not the same, actually. Your first array (lets, say $arr1) has 2 elements, while your second array (lets, say $arr2) has 4 elements in it.
Definitely, the first element of both the arrays (i.e., $arr1[0] and $arr2[0]) is an empty array and that part of the arrays are similar.
Now, the remaining part of the first array (i.e. $arr1[1]) is a string: ",2,2,1", while the remaining part of the second array are more array values: 2, 2, 1 and is not a string.
i.e.:
$arr1[1] #=> string: ,2,2,1
$arr2[1] #=> string: 2
$arr2[2] #=> string: 2
$arr2[3] #=> string: 1
And, therefore, you can clearly see the two arrays are not equal.
You can compare two arrays for equality (preserving the order) using the === operator, like this:
$arr1 === $arr2 #=> false
If you only want to check whether the two arrays have the same values (irrespective of their order), you should use the == operator.

Answer 2

Your arrays are not equal because you modify them in your code!
PHP:
// This is not an array, but a json string
js_array=<? echo json_encode($iState); ?>;
JS:
// Just pass the whole json string and don't use join!
xmlhttp.open("GET","fileB.php?istate="+ url_js_array,true);
xmlhttp.send();
PHP:
// Create an array again with json_decode
$iStateValues[] = json_decode($_GET["istate"]);
To your second question, this is how you could compare arrays in PHP:
$array1 = array(1, 2, 3); // This is the same like $array1 = array(0 => 1, 1 => 2, 2 => 3);
$array2 = array(1, 2, 4);
$array3 = array(3, 2, 1);
var_dump($array1 == $array2); // false
var_dump($array1 == $array3); // false
var_dump($array2 == $array3); // true
var_dump($array1 === $array2); // false
var_dump($array1 === $array3); // false
var_dump($array2 === $array3); // false
"==" checks for the same elements and "===" for the correct order. So in your case, '===' would deliver the correct answer.