headers_sent

说明

bool headers_sent ( [string &file [, int &line]] )

如果 HTTP 标头尚未被发送出去的话，headers_sent() 将返回 FALSE，否则返回 TRUE。如果指定了可选参数 file 和 line， headers_sent() 将会把 PHP 的文件名以及从哪一行开始有输出放到 file 和 line 变量中。

一旦标头已经被发送，将不能再使用 header() 函数来发送其它的标头。使用此函数至少可以避免避免与 HTTP 标头有关的错误信息。另一个选择是使用输出缓存。

注: 可选参数 file 和 line 是 PHP 4.3.0 版添加的。

例子 1. headers_sent() 例子
<?php // 如果尚未发送标头，发送一个 if (!headers_sent()) { header('Location: http://www.example.com/'); exit; } // 一个使用可选参数 file 和 line 的例子，自 PHP 4.3.0 起 // 注意 $filename 和 $linenum 被传递进来用于后续代码，不要预先赋值 if (!headers_sent($filename, $linenum)) { header('Location: http://www.example.com/'); exit; // 这里就触发了一个错误 } else { echo "Headers already sent in $filename on line $linenum\n" . "Cannot redirect, for now please click this <a " . "href=\"http://www.example.com\">link</a> instead\n"; exit; } ?>

相关问题的详细讨论参见 ob_start()，trigger_error() 和 header()。

add a note User Contributed Notes

rajnesh at gmail dot com
25-Feb-2006 02:19


headers_sent() will return FALSE if no HTTP headers have already been sent or TRUE otherwise. If the optional file and line parameters are set, headers_sent() will put the PHP source file name and line number where output started in the file and line variables. 



You can't add any more header lines using the header() function once the header block has already been sent. Using this function you can at least prevent getting HTTP header related error messages. Another option is to use Output Buffering. 



Note: The optional file and line parameters where added in PHP 4.3.0.

Jakob B.
07-Jan-2006 07:03


<?php

function redirect($filename) {

    if (!headers_sent())

        header('Location: '.$filename);

    else {

        echo '<script type="text/javascript">';

        echo 'window.location.href="'.$filename.'";';

        echo '</script>';

        echo '<noscript>';

        echo '<meta http-equiv="refresh" content="0;url='.$filename.'" />';

        echo '</noscript>';

    }

}

redirect('http://www.google.com');

?>

trevize (shtrudel) gmail.com
30-Nov-2005 10:43


Note that in IIS (or at least the version that comes with W2K server), the server seems to do some buffering, so even if you output someting or cause a warning, the value of headers_sent() may be false because the headers haven't been sent yet.



So it's not a safe way to know if warnings have been encountered in your script.

php [at] barryhunter [.] co [.] uk
09-Sep-2005 06:42


In responce to: Terry 11-Feb-2005 03:58 



if PHP is run as a Module, then it will behave as you describe



However if PHP is run as a CGI then it will be behave like Perl, (which uses CGI unless its mod_perl), as this is a CGI behaviour.



See http://ppewww.ph.gla.ac.uk/~flavell/www/perlcgifaq.html

alexrussell101 at gmail dot com
02-Sep-2005 06:31


To K.Tomono:



Headers are not sent as soon as you call the header() function. They are only sent as soon as some body content (i.e. HTML via echo or escaping from PHP parsing mode) is reached (or, like you did, you send a flush.) Thus after calling header a few times at the beginning they are still unsent and when you call headers_sent() it knows they haven't been sent and reports so. Only when the script ends or you output from content do all the headers so far send.

I think you misunderstood the way they are done and hopefully this should clear a few things up for you.

mark at dreamjunky dot com
29-Jun-2005 12:56


In case this comes up with anyone else, you might trigger headers to be sent if you have a PHP file with extra space after the closing ?>.  In particular, if you include that file at the top of your main script, it will cause headers to send, followed by the space after the ?> in your included script.  In short, make sure you don't have any space trailing your final ?>.

K.Tomono
22-Apr-2005 01:24


[code]

<?php

header("Cache-Control: private, must-revalidate, max-age=3600, post-check=3600, pre-check=3600");

////header("Last-Modified: " . gmdate("D, d M Y H:i:s",getlastmod())." GMT");

////ini_set("last_modified","1");

header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

flush(); // <= (*1)

...

if (!headers_sent()) {

  header('Content-Type:text/html; charset='._CHARSET);

  header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');

  //header('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT');

  header('Cache-Control: private, no-cache');

  header('Pragma: no-cache');

}

...

?>

[/code]



headers_sent() does not evaluate it as true, unless the flush()(*1) has been done.



It seems that it does not mean header was sent unless a header output is taken 

out to the exterior of PHP.



Apache 2.0.53 (prefork)

PHP 5.0.3 (server module)

... And XOOPS 2.0.9.2



I had seldom paid attention to flush() on PHP which is not C. 

However, it might have been a required thing.



[pre]

$ curl --cookie PHPSESSID=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX -i \

"http ://myhost.mydomain/xoops/modules/test.php?i=1" | less

  % Total    % Received % Xferd  Average Speed          Time             Curr.

                                 Dload  Upload Total    Current  Left    Speed

  0     0    0     0    0     0      0      0 --:--:--  0:00:00 --:--:--     0



HTTP/1.1 200 OK

Date: Fri, 22 Apr 2005 05:00:11 GMT

Server: Apache

X-Powered-By: PHP/5.0.3

Set-Cookie: PHPSESSID=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX; path=/

Expires: Thu, 19 Nov 1981 08:52:00 GMT

Cache-Control: private, must-revalidate, max-age=3600, post-check=3600, pre-check=3600

Pragma: no-cache

Last-Modified: Fri, 22 Apr 2005 05:00:11 GMT

Transfer-Encoding: chunked

Content-Type: text/html

[/pre]

(*)"http :" is "http:" in fact.

Terry
11-Feb-2005 11:58


For programmers used to Perl, note that sending a relative 'Location:' header sends a redirect to the browser in PHP, unlike Perl which will attempt to call relative URLs using an internal subrequest and return that page to the browser without redirecting.  If you want to do the same trick in PHP, use include() or virtual().

php at fufachew dot REMOVEME dot com
29-Feb-2004 03:26


RE: antti at haapakangas dot net's post



I've changed the code so $_SERVER['SERVER_NAME'] is used if $_SERVER['HTTP_HOST'] is not set.  $_SERVER['SERVER_NAME'] doesn't meet my needs, but I suppose it's good to fall back on it.  I've also fixed a problem in the meta refresh line - it was missing the "url=" part of the content attribute.



<?php

function server_url()

{   

    $proto = "http" .

        ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on") ? "s" : "") . "://";

    $server = isset($_SERVER['HTTP_HOST']) ?

        $_SERVER['HTTP_HOST'] : $_SERVER['SERVER_NAME'];

    return $proto . $server;

}

    

function redirect_rel($relative_url)

{

    $url = server_url() . dirname($_SERVER['PHP_SELF']) . "/" . $relative_url;

    if (!headers_sent())

    {

        header("Location: $url");

    }

    else

    {

        echo "<meta http-equiv=\"refresh\" content=\"0;url=$url\">\r\n";

    }

}

?>

antti at haapakangas dot net
29-Jan-2004 04:39


Re: php at fufachew dot com



That's a nice example how to implement Location header in a correct way (using absoluteURI). 95% of the scripts I have seen just use relativeURI which is wrong. Some browsers, for example lynx, actually notify user about incomplete Location headers. However it might be safer to use $_SERVER['SERVER_NAME'] instead of $_SERVER['HTTP_HOST']. Host header is a HTTP/1.1 feature and you can not count on that if you want to be interoperable with HTTP/1.0 implementations.

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