移动到函数时查询不起作用

Question

I have a query on index.php page that works perfectly. But when I move the query over to functions.php, create the the exact same query, it breaks. Any idea why?

index.php

<ul>
 <?php $cms_sub_pages = cms_find_sub_pages ($file_name); ?>
 <?php while($subpage = mysqli_fetch_assoc($cms_sub_pages)) { ?>
   <li><a href="/edit.php?
       <?php echo $subpage["page_id"]; ?>"><?php echo $subpage["link_name"]; ?></a
   </li>    
 <?php
 }
 ?>
 <?php mysqli_free_result($sub_pages); ?>
 </ul>

functions.php

function cms_find_sub_pages ($file_name) {
    global $conn;

    $query = "SELECT * FROM pages WHERE main_cat = 2 AND category =  '{$file_name}' ORDER BY subcategory_order ASC ";
    $sub_pages = mysqli_query($conn, $query);
    confirm_query($sub_pages);
    return $sub_pages;  
}

SOLVED: The issue was in index.php here:

<?php $cms_sub_pages = cms_find_sub_pages ($file_name); ?>

Changed to:

<?php $cms_sub_pages = cms_find_sub_pages ($mainpage["page_id"]); ?>

Answer 1

Undefined variable $file_name.

Use

function cms_find_sub_pages ($file_name) {

OR

function cms_find_sub_pages () {
    global $conn, $file_name;

Please, use error_reporting(E_ALL); from header.php for debug your scripts.

P.S. Sorry my english