November 2002
Intermediate to advanced
640 pages
16h 33m
English
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8.18. Eliminating “headers already sent” Errors
Problem
You are trying to send a
HTTP header or cookie using header( )
or setcookie( ),
but PHP reports a
“headers already
sent” error message.
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>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 ...