headers_sent
(PHP 3 >= 3.0.8, PHP 4, PHP 5)
headers_sent -- Checks if or where headers have been sent
Description
bool
headers_sent ( [string &file [, int &line]] )
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.
注:
The optional file and line
parameters where added in PHP 4.3.0.
例子 1. Examples using headers_sent()
<?php
// If no headers are sent, send one
if (!headers_sent()) {
header('Location: http://www.example.com/');
exit;
}
// An example using the optional file and line parameters, as of PHP 4.3.0
// Note that $filename and $linenum are passed in for later use.
// Do not assign them values beforehand.
if (!headers_sent($filename, $linenum)) {
header('Location: http://www.example.com/');
exit;
// You would most likely trigger an error here.
} 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;
}
?>
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See also ob_start(), trigger_error(),
and header() for a more detailed discussion of the
matters involved.