Warning: Cannot modify header information - headers already sent

Question

I've just received this error/warning after trying to upload an image, any ideas what it means and what I can do to fix it?

Warning: Cannot modify header information - headers already sent by (output started at /home/achenn/public_html/wp-content/themes/whskytngfxtrt/functions.php:14) in /home/achenn/public_html/wp-includes/pluggable.php on line 866

Here's my site, live.

functions.php:

<?php

// sidebar functions

if(function_exists('register_sidebar'))
{
    register_sidebar();
}


?>


<?php

// portfolio functions

    add_action('init', 'create_portfolio');
    function create_portfolio() {
        $portfolio_args = array(
            'label' => __('Portfolio'),
            'singular_label' => __('Portfolio'),
            'public' => true,
            'show_ui' => true,
            'capability_type' => 'post',
            'hierarchical' => false,
            'rewrite' => true,
            'supports' => array('title', 'editor', 'thumbnail')
        );
        register_post_type('portfolio',$portfolio_args);
    }
?>

<?php

// custom input- portfolio backend

    add_action("admin_init", "add_portfolio");
    add_action('save_post', 'update_website_url');
    function add_portfolio(){
        add_meta_box("portfolio_details", "Portfolio Options", "portfolio_options", "portfolio", "normal", "low");
    }
    function portfolio_options(){
        global $post;
        $custom = get_post_custom($post->ID);
        $website_url = $custom["website_url"][0];
?>
    <div id="portfolio-options">
        <label>Website URL:</label><input name="website_url" value="<?php echo $website_url; ?>" />     
    </div><!--end portfolio-options-->   
<?php
    }
    function update_website_url(){
        global $post;
        update_post_meta($post->ID, "website_url", $_POST["website_url"]);
    }
?>

<?php 

// detail columns- portfolio backend

add_filter("manage_edit-portfolio_columns", "portfolio_edit_columns");
add_action("manage_posts_custom_column",  "portfolio_columns_display");

function portfolio_edit_columns($portfolio_columns){
    $portfolio_columns = array(
        "cb" => "<input type=\"checkbox\" />",
        "title" => "Project Title",
        "description" => "Description",
    );
    return $portfolio_columns;
}

function portfolio_columns_display($portfolio_columns){
    switch ($portfolio_columns)
    {
        case "description":
            the_excerpt();
            break;              
    }
}
?>

portfolio.php-

<?php
/*
Template Name: Portfolio
*/
?>
<?php get_header(); ?>
    <div id="content">
    <?php 
        $loop = new WP_Query(array('post_type' => 'portfolio', 'posts_per_page' => 10)); 
    ?>
    <?php while ( $loop->have_posts() ) : $loop->the_post(); ?>
    <?php   
        $custom = get_post_custom($post->ID);
        $screenshot_url = $custom["screenshot_url"][0];
        $website_url = $custom["website_url"][0];
    ?>
        <div id="portfolio-item">
        <h1><?php the_title(); ?></h1>
        <a href="<?=$website_url?>"><?php the_post_thumbnail(); ?> </a>
        <?php the_content(); ?>
    </div>
        <?php endwhile; ?>  
        </div><!-- #content -->
<?php get_footer(); ?>

Answer 1

From the looks of things, some page is trying to load your functions.php page directly. I'm not sure if it's another part of your theme, or a plugin, or some other custom code. But the error on line 14 is triggered with a second <?php opening tag in your functions.php file.

This headers already sent error is triggered when you send any additional whitespace, line returns, or text when you're not supposed to. A short-term fix is to remove the extra markup:

<?php // sidebar functions
if(function_exists('register_sidebar')) {
    register_sidebar();
}

// portfolio functions
add_action('init', 'create_portfolio');

See how much more compact that is? No extra white space between ?> and <?php either.

For the long-term, though, you need to narrow down exactly what you're doing. Where are you uploading the image from? Why is it trying to redirect to your functions.php file? Answer those questions and fix whatever problems are causing the issues for a more durable fix.