"Warning: Cannot modify header information" error in wordpress

Question

I am having this error in a developing plugin.
Works fine in localhost but in the remote server fails with:

Warning: Cannot modify header information - headers already sent by (output started at /path_wordpress/public_html/wp-admin/includes/template.php:1657) in /path_wordpress/public_html/wp-includes/pluggable.php on line 866

I have removed all spaces before and after at the beginning and end of files (the common reason for this error) and there are no sessions involved.

What another reasons could be?

===
EDIT 1

wp-admin/includes/template.php:

$attributes = '';
if ( is_array( $other_attributes ) ) {
    foreach ( $other_attributes as $attribute => $value ) { // line 1657 
        $attributes .= $attribute . '="' . esc_attr( $value ) . '" '; // Trailing space is important
    }
} else if ( !empty( $other_attributes ) ) { // Attributes provided as a string
    $attributes = $other_attributes;
}

===
EDIT 2:

wp-admin/wp-includes/pluggable.php:

if ( !function_exists('wp_redirect') ) :
/**
 * Redirects to another page.
 *
 * @since 1.5.1
 * @uses apply_filters() Calls 'wp_redirect' hook on $location and $status.
 *
 * @param string $location The path to redirect to
 * @param int $status Status code to use
 * @return bool False if $location is not set
 */ // line 866
function wp_redirect($location, $status = 302) {
    global $is_IIS;

Have any code? Also, do you know what the offending `header` is? — William Isted, Jul 03 '12 at 22:56
Another reason: you are sending output more than once. Anyway, we need code to review — Alfabravo, Jul 03 '12 at 22:57
Do you see any part of template before this error, if so then the template has been already echoed. — The Alpha, Jul 03 '12 at 23:02
The plugin have several files, so I can't put code here. I don't know what file is causing this error.... — Igor Parra, Jul 03 '12 at 23:05
@sheikh-heera No, no template output. This error occur in the admin panel. — Igor Parra, Jul 03 '12 at 23:09
@NomikOS What's on this line /path_wordpress/public_html/wp-admin/includes/template.php:1657 — William Isted, Jul 03 '12 at 23:09
@william-isted question edited to show what you ask, thanks! — Igor Parra, Jul 03 '12 at 23:14
You need to look at `/path_wordpress/public_html/wp-includes/pluggable.php on line 866` — Steve Robbins, Jul 03 '12 at 23:16
@NomikOS I'm sure you already know that there appears to be nothing that would cause the problem on that line, out of interest what happens when you comment out the block of code you have shown? — William Isted, Jul 03 '12 at 23:19
Did you used `die()` or `exit()` after `wp_redirect()` call ? — The Alpha, Jul 03 '12 at 23:34
remove the closing php tag `?>` from your plugin files to be sure that you have no captured whitespace — Roscius, Jul 03 '12 at 23:36
@mario Please answers for give you the 15. It was very helpful, thanks! — Igor Parra, Jul 04 '12 at 00:34

score 1 · Answer 1 · answered Jul 04 '12 at 02:54

1

Cannot modify header information usually occurs when you try to use header() or redirect function after some html has been outputted. It is unlikely to be inside one of Wordpress native code files, so check some custom code you might have written that tries to redirect the page.

Reference: http://php.net/manual/en/function.header.php

answered Jul 04 '12 at 02:54

anuragbh

603
1
5
11

Thanks, was stuck on this for some time, but you were spot on "Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP" – Bwyss Mar 22 '13 at 20:51

"Warning: Cannot modify header information" error in wordpress

1 Answers1