Titles can only be retrieved in PHP via curl - header only retrieval in PHP via curl

problem ：

Actually I have two questions. Actually, I have two questions .

(1) Is there any reduction in processing power or bandwidth used on remote server if I retrieve only headers as opposed to full page retrieval using php and curl?（1） If I only retrieve the title instead of using php and curl Perform a full page search , Then the remote server used processing capacity or bandwidth Will it decrease ？

(2) Since I think, and I might be wrong, that answer to first questions is YES , I am trying to get last modified date or If-Modified-Since header of remote file only in order to compare it with time-date of locally stored data, so I can, in case it has been changed, store it locally.（2） Because I think , I may be wrong , The answer to the first question is For sure , I try to get the last modification date or If-Modified-Since The remote file of the title is only to compare it with the time and date, and the locally stored data , So I can , If it has been changed , Store it locally .However, my script seems unable to fetch that piece of info, I get NULL , when I run this: however , When I run this , My script doesn't seem to get this information , I got NULL ：

class last_change { public last_change; function set_last_change() {  $curl = curl_init();    curl_setopt($curl, CURLOPT_URL, "http://url/file.xml");    curl_setopt($curl, CURLOPT_HEADER, true);    curl_setopt($curl, CURLOPT_FILETIME, true);    curl_setopt($curl, CURLOPT_NOBODY, true);  // $header = curl_exec($curl);  $this -> last_change = curl_getinfo($header);  curl_close($curl); } function get_last_change() {  return $this -> last_change['datetime']; // I have tested with Last-Modified & If-Modified-Since to no avail }}

In case $header = curl_exec($curl) is uncomented, header data is displayed, even if I haven't requested it and is as follows: If $header = curl_exec($curl) Not enabled , Then the header data is displayed , Even if I didn't ask it , As shown below ：

HTTP/1.1 200 OKDate: Fri, 04 Sep 2009 12:15:51 GMTServer: Apache/2.2.8 (Linux/SUSE)Last-Modified: Thu, 03 Sep 2009 12:46:54 GMTETag: "198054-118c-472abc735ab80"Accept-Ranges: bytesContent-Length: 4492Content-Type: text/xml

Based on that, 'Last-Modified' is returned. On this basis , return “Last-Modified”.

So, what am I doing wrong? that , What did I do wrong ？

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Solution ：

Reference resources ： https://stackoom.com/en/question/5miZ