如何删除xml网站地图开头的空格：<？xml version=“1.0” encoding=“UTF-8”？>？

问：

我在浏览器上访问站点地图.xml时出现此错误

error on line 1 at column 7: XML declaration allowed only at the start of the document
Below is a rendering of the page up to the first error.

经过一番调查，我了解到开始空格导致了问题。

     <?xml version="1.0" encoding="UTF-8"?>
<urlset 

以下代码生成 xml 标记：

<?php
class Sitemap extends CI_Controller {
    function __construct() {
        parent::__construct();
        $this->load->model('sitemap_', 'sitemap');
        //$this->load->model('deals_', 'deals');
        //$this->load->library('ravresponse'); 
    }

    public function xml() {
        $website_id  = (int)$this->ravconfig->get('config_website_id');
        //$language_id = (int)$this->ravconfig->get('config_language_id');

        if (isset($this->request->server['HTTPS']) && $this->request->server['HTTPS'])  {
            $server = $this->ravconfig->get('config_ssl');
        } else {
            $server = $this->ravconfig->get('config_url');
        }

        header('Content-Type: application/xml');
        $output = '';
        $output .= '<?xml version="1.0" encoding="UTF-8"?>';
        $output .= "\n".'<urlset 
        xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" 
        xmlns:xhtml="http://www.w3.org/1999/xhtml" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">';


        // Retrieve languages assigned to website
        $raw_languages = $this->sitemap->getAssignedLanguages($website_id);

        if($raw_languages) {
            $raw_languages = unserialize($raw_languages['value']);
            $languages = $raw_languages['language'];
        }

        //print_r($languages);

        // Home Page
        $output .= "\n\t".'<url>';
        $output .= "\n\t\t".'<loc>' . $server. '</loc>';
        $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
        $output .= "\n\t\t".'<priority>1.00</priority>';
        $output .= "\n\t".'</url>';

        // Information Pages
        $information_pages = $this->sitemap->getInformationPages($website_id);

        if($information_pages) {
            foreach($information_pages as $information_page) {
                foreach($languages as $key => $language_id) {
                    $output .= "\n\t".'<url>';
                    $output .= "\n\t\t".'<loc>' . $this->link->geturl('information_id=' . $information_page['information_id'], "", $language_id, $website_id). '</loc>';
                    $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                    $output .= "\n\t\t".'<priority>0.70</priority>';
                    $output .= "\n\t".'</url>';
                }
            }
        }

        // Independent Pages
        $independent_pages = $this->sitemap->getIndependentPages($website_id);

        if($independent_pages) {
            foreach($independent_pages as $independent_page) {
                foreach($languages as $key => $language_id) {
                    $output .= "\n\t".'<url>';
                    $output .= "\n\t\t".'<loc>' . $this->link->geturl('independent_page_id=' . $independent_page['independent_page_id'], "", $language_id, $website_id). '</loc>';
                    $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                    $output .= "\n\t\t".'<priority>0.70</priority>';
                    $output .= "\n\t".'</url>';
                }
            }
        }

        // Destination Pages
        $destination_pages = $this->sitemap->getDestinationPages($website_id);

        if($destination_pages) {
            foreach($destination_pages as $destination_page) {
                foreach($languages as $key => $language_id) {
                    $output .= "\n\t".'<url>';
                    $output .= "\n\t\t".'<loc>' . $this->link->geturl('destination_id=' . $destination_page['destination_id'], "", $language_id, $website_id). '</loc>';
                    $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                    $output .= "\n\t\t".'<priority>0.70</priority>';
                    $output .= "\n\t".'</url>';
                }
            }
        }

        // Category Pages
        $category_pages = $this->sitemap->getCategoryPages($website_id);

        if($category_pages) {
            foreach($category_pages as $category_page) {
                foreach($languages as $key => $language_id) {
                    $output .= "\n\t".'<url>';
                    $output .= "\n\t\t".'<loc>' . $this->link->geturl('category_id=' . $category_page['category_id'], "", $language_id, $website_id). '</loc>';
                    $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                    $output .= "\n\t\t".'<priority>0.70</priority>';
                    $output .= "\n\t".'</url>';
                }
            }
        }

        // Product Pages

        if($category_pages) {
            foreach($category_pages as $category_page) {

                $product_pages = $this->sitemap->getProductPages($category_page['category_id'], $website_id);

                foreach($product_pages as $product_page) {
                    foreach($languages as $key => $language_id) {
                        $output .= "\n\t".'<url>';
                        $output .= "\n\t\t".'<loc>' . $this->link->geturl('product_id=' . $product_page['product_id'], "", $language_id, $website_id). '</loc>';
                        $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                        $output .= "\n\t\t".'<priority>0.70</priority>';
                        $output .= "\n\t".'</url>';
                    }
                }
            }
        }

        // Blog Pages
        $blog_pages = $this->sitemap->getBlogPages($website_id);

        if($blog_pages) {
            foreach($blog_pages as $blog_page) {
                $output .= "\n\t".'<url>';
                $output .= "\n\t\t".'<loc>' . $this->link->geturl('blog_id=' . $blog_page['blog_id'], "", $blog_page['language_id'], $website_id). '</loc>';
                $output .= "\n\t\t".'<changefreq>weekly</changefreq>';
                $output .= "\n\t\t".'<priority>0.70</priority>';
                $output .= "\n\t".'</url>';
            }
        }

        $output .= "\n".'</urlset>';

        print($output);
    }
}

请问是什么导致了这个额外的空间吗？

我尝试删除代码破译行中的空格，但没有运气。 还试图呼应第一个标签，但仍创建空间。