Question

I have two files:

cart_function.php

function get_product_name($pid){
    $result = mysql_query("SELECT product_name FROM product_table WHERE product_id='".$pid."'", $link);
    $row = mysql_fetch_array($result);
    return $row['product_name'];
}

cart.php

<?php
    include('cart_function.php');
    $pid = $_GET['product_id'];
    $pname = get_product_name($pid);
    echo $pname;
?>

After I execute the cart.php, it shows an error

supplied argument is not a valid MySQL-Link resource’

If I run the query directly in MySQL database it works perfectly. If I used the get_product_name() function directly in cart.php, again it’s not working. But if I remove the function and use the code below, it works:

<?php
    $pid = $_GET['product_id'];
    $result = mysql_query("SELECT product_name FROM product_table WHERE product_id='".$pid."'",$link);
    $row = mysql_fetch_array($result);
    $pname = $row['product_name'];
    echo $pname;
?>

Why?

Answer 1

The problem is here:

function get_product_name($pid){
    $result = mysql_query("SELECT product_name FROM product_table WHERE product_id='".$pid."'",
                          $link);

You have written $link, but its value is not supplied. You have to pass this value in the function argument as you are passing $pid value, like this:

function get_product_name($pid,$link){