Recipe 8.19 Eliminating "headers already sent" Errors
8.19.1 Problem
You are trying to send a
HTTP header or cookie using header(
) or setcookie( ),
but PHP reports a
"headers already
sent" error message.
8.19.2 Solution
This error happens when you send nonheader output before calling
header( ) or setcookie( ).
Rewrite your code so any output happens after sending headers:
// good
setcookie("name", $name);
print "Hello $name!";
// bad
print "Hello $name!";
setcookie("name", $name);
// good
<?php setcookie("name",$name); ?>
<html><title>Hello</title>
8.19.3 Discussion
An HTTP message has a header and a body, which are sent to the client
in that order. Once you begin sending the body, you
can't send any more headers. So, if you call
setcookie( ) after printing some HTML, PHP
can't send the appropriate Cookie
header.
Also, remove trailing whitespace in any
include files. When you include a file
with blank lines outside <?php ?> tags, the
blank lines are sent to the browser. Use trim(
) to
remove leading and trailing blank lines from files:
$file = '/path/to/file.php';
// backup
copy($file, "$file.bak") or die("Can't copy $file: $php_errormsg);
// read and trim
$contents = trim(join('',file($file)));
// write
$fh = fopen($file, 'w') or die("Can't open $file for writing: $php_errormsg);
if (-1 == fwrite($fh, $contents)) { die("Can't write to $file: $php_errormsg); }
fclose($fh) or die("Can't close $file: $php_errormsg);
Instead of processing files on a one-by-one basis, it may be more
convenient to do so on a directory-by-directory basis. Recipe 19.8 describes how to process all the files in a
directory.
If you don't want to worry about blank lines
disrupting the sending of headers, turn on
output buffering.
Output buffering prevents PHP from immediately sending all output to
the client. If you buffer your output, you can intermix headers and
body text with abandon. However, it may seem to users that your
server takes longer to fulfill their requests since they have to wait
slightly longer before the browser displays any output.
8.19.4 See Also
Recipe 8.13 discusses output buffering;
Recipe 19.8 for processing all files in a
directory; documentation on header( ) at
http://www.php.net/header.
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