If you are using output buffering and you use the flush() command ANYWHERE headers_sent() will return true - even if the buffer is seemingly empty.
headers_sent
(PHP 4, PHP 5)
headers_sent — ヘッダが既に送信されているかどうかを調べる
説明
bool headers_sent ( [string &$file [, int &$line]] )headers_sent() は、HTTP ヘッダが既に送信されている場合に TRUE 、そうでない場合に FALSE を返します。 また、オプション引数の file と line がセットされている場合、 PHP のソースファイル名と出力が開始された行番号が、それぞれ file と line に格納されます。
ヘッダブロックがいったん送信されてしまった後で header() 関数を使って新たなヘッダ行を送信することはできません。 この関数を使うには、少なくとも HTTP ヘッダ関連のエラーを予防する必要があります。 あるいは、出力バッファリングを 使う方法もあります。
注意: オプションのパラメータ file と line が PHP 4.3.0 で追加されました。
例 1543. headers_sent() 関数の使用例
<?php
// ヘッダがまだ何も送信されていない場合に、送信します
if (!headers_sent()) {
header('Location: http://www.example.com/');
exit;
}
// オプションのfileとlineパラメータの使用例（PHP4.3.0以降）
// $filename と $linenum が後で使用されていることに注目。
// これらの変数に事前に値を与えたりしてはいけません。
if (!headers_sent($filename, $linenum)) {
header('Location: http://www.example.com/');
exit;
// おそらく、ここでエラー処理を行うでしょう。
} else {
echo "$filename の $linenum 行目でヘッダがすでに送信されています。\n" .
"リダイレクトできません。代わりにこの <a " .
"href=\"http://www.example.com\">リンク</a> をクリックしてください。\n";
exit;
}
?>
これに関連するより詳細な議論は ob_start()、 trigger_error()、 header() を参照ください。
headers_sent
kamermans at teratechnologies dot net
22-Aug-2006 05:24
22-Aug-2006 05:24
rajnesh at gmail dot com
25-Feb-2006 03:19
25-Feb-2006 03:19
headers_sent() will return FALSE if no HTTP headers have already been sent or TRUE otherwise. If the optional file and line parameters are set, headers_sent() will put the PHP source file name and line number where output started in the file and line variables.
You can't add any more header lines using the header() function once the header block has already been sent. Using this function you can at least prevent getting HTTP header related error messages. Another option is to use Output Buffering.
Note: The optional file and line parameters where added in PHP 4.3.0.
Jakob B.
07-Jan-2006 08:03
07-Jan-2006 08:03
<?php
function redirect($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 11:43
30-Nov-2005 11:43
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 07:42
09-Sep-2005 07:42
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 07:31
02-Sep-2005 07:31
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 01:56
29-Jun-2005 01:56
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 02:24
22-Apr-2005 02:24
[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 12:58
11-Feb-2005 12:58
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 04:26
29-Feb-2004 04:26
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 05:39
29-Jan-2004 05:39
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.