我的strlen和substr PHP有什么问题

Question

I created a session called product_ . When i click in my add to cart button, my

$_SESSION['product_' . $_GET['add']] will be like this product_171 the 171 is the id from a product that i have. I printed out my query to see what's going on and my item_id is not echoing 171 it's sendind 17 not 171. i tryed to change the numbers but it didn't work.

this is my code.

function cart(){
    global $conn;
    foreach ($_SESSION as $name => $value) {
        if($value > 0){

        if(substr($name, 0, 8 ) == "product_"){
            $length = strlen($name -8);
            $item_id = substr($name, 8 , $length);

    $query = "SELECT * FROM gallery2 WHERE id =".escape_string($item_id)."";
    print_r($name); echo' <strong>this is the name</strong></br>';
    print_r($item_id); echo'  <strong>this is the id without the name -product_</strong></br>';...

this is what i'm getting

product_171 this is the name

17 this is the id without the name -product_ why im not getting my full id?

Answer 1

The piece of code where you check the string length is wrong:

if(substr($name, 0, 8 ) == "product_"){
        $length = strlen($name -8);
        $item_id = substr($name, 8 , $length);
...

You are checking strlen of $name - 8, and $name - 8 is equal to -8, that have 2 characters, so it will always get 2 characters.

The -8 should be out of the strlen() function:

if(substr($name, 0, 8 ) == "product_"){
        $length = strlen($name) - 8;
        $item_id = substr($name, 8 , $length);
...