Warning: Cannot modify header information - headers already sent by in wordpress

Question

unable to add contents in pages like about us ,courses,contact us..while adding the content error is displaying

Warning: Cannot modify header information - headers already sent by (output started at /home/phptraining/public_html/wp-content/themes/health-center-lite/functions.php:95) in /home/phptraining/public_html/wp-admin/post.php on line 235

and

Warning: Cannot modify header information - headers already sent by (output started at /home/phptraining/public_html/wp-content/themes/health-center-lite/functions.php:95) in /home/phptraining/public_html/wp-includes/pluggable.php on line 1196

functions.php

    <?php   /**Includes reqired resources here**/
        define('WEBRITI_TEMPLATE_DIR_URI',get_template_directory_uri());    
        define('WEBRITI_TEMPLATE_DIR',get_template_directory());
        define('WEBRITI_THEME_FUNCTIONS_PATH',WEBRITI_TEMPLATE_DIR.'/functions');   
        define('WEBRITI_THEME_OPTIONS_PATH',WEBRITI_TEMPLATE_DIR_URI.'/functions/theme_options');

        require( WEBRITI_THEME_FUNCTIONS_PATH . '/menu/default_menu_walker.php' ); // for Default Menus
        require( WEBRITI_THEME_FUNCTIONS_PATH . '/menu/webriti_nav_walker.php' ); // for Custom Menus   

        require( WEBRITI_THEME_FUNCTIONS_PATH . '/commentbox/comment-function.php' ); //for comments
        require( WEBRITI_THEME_FUNCTIONS_PATH . '/widget/custom-sidebar.php' ); //for widget register


        //content width
        if ( ! isset( $content_width ) ) $content_width = 900;      
        //wp title tag starts here
        function hc_head( $title, $sep )
        {   global $paged, $page;       
            if ( is_feed() )
                return $title;
            // Add the site name.
            $title .= get_bloginfo( 'name' );
            // Add the site description for the home/front page.
            $site_description = get_bloginfo( 'description' );
            if ( $site_description && ( is_home() || is_front_page() ) )
                $title = "$title $sep $site_description";
            // Add a page number if necessary.
            if ( $paged >= 2 || $page >= 2 )
                $title = "$title $sep " . sprintf( _e( 'Page', 'helth' ), max( $paged, $page ) );
            return $title;
        }   
        add_filter( 'wp_title', 'hc_head', 10,2 );

        add_action( 'after_setup_theme', 'hc_setup' );  
        function hc_setup()
        {   // Load text domain for translation-ready
            load_theme_textdomain( 'health', WEBRITI_THEME_FUNCTIONS_PATH . '/lang' );      

            add_theme_support( 'post-thumbnails' ); //supports featured image
            // This theme uses wp_nav_menu() in one location.
            register_nav_menu( 'primary', __( 'Primary Menu', 'health' ) );
            // theme support    
            $args = array('default-color' => '000000',);
            add_theme_support( 'custom-background', $args  ); 
            add_theme_support( 'automatic-feed-links'); 

            require_once('theme_setup_data.php');
            require( WEBRITI_THEME_FUNCTIONS_PATH . '/theme_options/option_pannel.php' ); // for Custom Menus       
            // setup admin pannel defual data for index page        
            $health_center_lite_theme=theme_data_setup();

            function hc_custom_excerpt_length( $length ) {  return 50; }
            add_filter( 'excerpt_length', 'hc_custom_excerpt_length', 999 );

            function hc_new_excerpt_more( $more ) { return '';}
            add_filter('excerpt_more', 'hc_new_excerpt_more');

            $current_theme_options = get_option('hc_lite_options'); // get existing option data         
            if($current_theme_options)
            {   $hc_lite_theme_options = array_merge($health_center_lite_theme, $current_theme_options);
                update_option('hc_lite_options',$hc_lite_theme_options);            
            }
            else
            {   add_option('hc_lite_options',$health_center_lite_theme);    }


        }
        /******** health center js and cs *********/
        function hc_scripts()
        {   // Theme Css 
            wp_enqueue_style('health-responsive', WEBRITI_TEMPLATE_DIR_URI . '/css/media-responsive.css');

            wp_enqueue_style('health-font', WEBRITI_TEMPLATE_DIR_URI . '/css/font/font.css');   

            wp_enqueue_style('health-bootstrap', WEBRITI_TEMPLATE_DIR_URI . '/css/bootstrap.css');  

            wp_enqueue_style('health-font-awesome', WEBRITI_TEMPLATE_DIR_URI . '/css/font-awesome-4.0.3/css/font-awesome.min.css'); 

            wp_enqueue_script('health-menu', WEBRITI_TEMPLATE_DIR_URI .'/js/menu/menu.js',array('jquery'));

            wp_enqueue_script('health-bootstrap_min', WEBRITI_TEMPLATE_DIR_URI .'/js/bootstrap.min.js');    
        }

        add_action('wp_enqueue_scripts', 'hc_scripts');
        if ( is_singular() ){ wp_enqueue_script( "comment-reply" ); }

        // Read more tag to formatting in blog page 
        function hc_content_more($more)
        {  global $post;
           return ' <a href="' . get_permalink() . "#more-{$post->ID}\" class=\"hc_blog_btn\">Read More<i class='fa fa-long-arrow-right'></i></a>";
        }   
        add_filter( 'the_content_more_link', 'hc_content_more' );
       ?>

       <?php
    /**
     * Register Widget Area.
     *
     */
    function wpgyan_widgets_init() {

        register_sidebar( array(
            'name' => 'Header Sidebar',
            'id' => 'header_sidebar',
            'before_widget' => '<div>',
            'after_widget' => '</div>',
            'before_title' => '<h2 class="rounded">',
            'after_title' => '</h2>',
        ) );
    }
    add_action( 'widgets_init', 'wpgyan_widgets_init' );
    ?>

Answer 1

This has nothing to do with functions.php sending headers. Rather, it has to do with output having started (in the functions file) before headers are sent (by other WordPress scripts). What you'll see, if you look on line 95, is the following:

?>

<?php

That blank line between the closing and opening PHP tags is the cause of the error. Instead, you should get rid of both of those tags, so that your code becomes:

add_filter( 'the_content_more_link', 'hc_content_more' );

/**
 * Register Widget Area.
 *
 */
function wpgyan_widgets_init() {

While you're at it, also delete the last line of your functions.php file (the closing ?> PHP tag). It's unnecessary here.

Answer 2

This error is not specific to wordpress. This is a standard error of PHP. This problem is occurring because you are trying to modify headers after an output is generated in that page like php echo or some html is rendered.

I hope this helps you.