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Why can't I use session_start () in my PHP script? He says headers are already sent

Here are the first few lines of my page:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <?php include_once "dblogin.php"; session_start(); $loggedIn = 0; if(isset($_SESSION["login"])) {$loggedIn = 1;} ?>

I get the following error:

Unable to send session cookie - headers already sent (output started in /usr/www/users/simpleof/index.php-2) in / usr / www / users / simpleof / index.php on line 2

From what I read in other forums, this should be good, because session_start () is in the first block of php code, but I still get this error.

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2 answers

You either read incorrectly or other forums are mistaken. Just because session_start() is in the first "block" of PHP code does not mean that it will work.

session_start() must be started before sending headers.

The solution in your case:

Move session_start(); above <!DOCTYPE html ...

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Here's how the HTTP protocol works:

You send this kind of header to your browser:

 GET /questions/712326/why-cant-i-use-sessionstart-in-my-php-script-it-says-headers-are-already-sen HTTP/1.1 Host: stackoverflow.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; fi; rv:1.9.0.8) Gecko/2009032609 Firefox/3.0.8 (.NET CLR 3.5.30729) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: fi-fi,fi;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://stackoverflow.com/questions/tagged/php Cookie: *censored* Cache-Control: max-age=0

The first server sends you headers:

 HTTP/1.x 200 OK Cache-Control: private Content-Type: text/html; charset=utf-8 Content-Encoding: gzip Expires: Fri, 03 Apr 2009 02:14:49 GMT Vary: Accept-Encoding Server: Microsoft-IIS/7.0 Set-Cookie: *censored* Date: Fri, 03 Apr 2009 02:14:49 GMT Content-Length: 9346

The server then sends you the actual page data.

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd" > <html> <head> <title>Why can't I use session_start() in my PHP ? It says headers are already sent. - Stack Overflow</title> <link rel="stylesheet" href="/Content/all.min.css?v=2743"> ..snip..

So you see that you cannot transfer the HTML data (DOCTYPE) and then the header data, because the header has already been processed. You can go with PHP Output Control , but it is more recommended to use MVC , where you buffer all the data that the user sees last.

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