如何刪除由特定的ID的XML節點在php

Question

這是PHP代碼

<?php 
    function delete_book_id($id, $filename = 'books.xml'){ 
     $data = simplexml_load_file($filename); 
     for($i = 0, $length = count($data->resource->book); $i < $length; $i++){ 
     if($data->resource->book[$i]->ID == $id){ 
     unset($data->resource->book[$i]); 
     break; 
    } 
    } 
    file_put_contents($filename, $data->saveXML()); 
    } 
    //SAMPLE USAGE 
    delete_book_id('$id'); 
    ?> 

XML文件中以下

<?xml version="1.0" encoding="utf-8"?> 
<catalogue> 
<resource> 
    <book> 
    <ID>Book 1</ID> 
    <date>today</date> 
    <retdate>tomorrow</retdate> 
    <SID>Student 1</SID> 
    </book> 
    <book> 
    <ID>Book 2</ID> 
    <date>toda</date> 
    <retdate>tomorro</retdate> 
    <SID>Student 2</SID> 
    </book> 

    </resource> 
    </catalogue> 

請幫我得到答案。下面

Answer 1

變化：

delete_book_id('$id'); 

要：

delete_book_id($id); 

爲我工作。