i was following atutorial on how to make a custom metabox to wordpress post but its giving errors

here is my full code

//Add Metabox
function diwp_custom_metabox(){
    //add_meta_box(metabox_id,metabox name,callback function,metabox location(page,post,custom post etc),context-(normal,side,advanced),piority())
    add_meta_box('diwp-metabox','My Custom Metabox','diwp_post_metabox_callback','post','normal');

//add action
//metabox callback function

function diwp_post_metabox_callback(){
    // echo 'hi i am diwp metabox';
    <div class="row">
      <div class="label">Post Reading Time</div>
      <div class="fields">
        <input type="text" name="_diwp_reading_time" value="<?php get_post_meta($post->ID,'post_reading_time',true); ?>">

function diwp_save_custom_metabox(){
    // update_post_meta($post_id,$meta_key,$meta_value,$prev_value);
    global $post;


error screen shot enter image description here

any help will be appreciated ,thanks

1 Answer 1


The error there clearly says that there's an undefined variable (post) in your metabox callback function.

So you need to define $post in your function head:

// The $post variable is passed by WordPress.
function diwp_post_metabox_callback( $post )

And you should also do the same to diwp_save_custom_metabox() function (which is hooked to save_post):

// Here, $post is the second parameter.
function diwp_save_custom_metabox( $post_ID, $post ) {
    // ...

// Don't forget to set the 4th parameter to 2:
add_action( 'save_post', 'diwp_save_custom_metabox', 10, 2 );

Or alternatively, use get_post() and not the global call:

// Here, $post is the second parameter.
function diwp_save_custom_metabox( $post_ID ) {
    $post = get_post( $post_ID ); // like this
//  global $post;                 // not this

    // ...

add_action( 'save_post', 'diwp_save_custom_metabox' );
  • hello thanks for reply and code works but can you please explain what 10 and 2 means in this line add_action( 'save_post', 'diwp_save_custom_metabox', 10, 2 ); ..i have seen that im few tutorials but didnt understand what that means? and to output the meta field data on front end i am using this code echo get_post_meta( $post->ID, 'post_reading_time', true ); is it ok?
    – Sash_007
    Oct 10, 2020 at 3:54
  • Yes, that's fine. And check out the docs for add_action() here, but the 10 means the callback's priority - if there were 4 callbacks hooked to save_post, that priority determines the position of your own callback, e.g. is it the first or last one that executes. And the 2 is the number of args your callback accepts, but you need to check the hook docs (e.g. this for save_post) to know all the args for that specific hook.
    – Sally CJ
    Oct 11, 2020 at 6:13
  • You should also validate, sanitize and escape user data, e.g. use esc_attr() with the <input>'s value and esc_html() when displaying the value, e.g. echo esc_html( get_post_meta( ... ) ).
    – Sally CJ
    Oct 11, 2020 at 10:35
  • ok i have used wp nonce along with esc_html let me know if its ok ..check here ... pastebin.com/d3Y4vS3x
    – Sash_007
    Oct 16, 2020 at 4:08

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