How to write to wp-users table

Question

I'm trying to modify a login plugin to make new users to to enter the display name to show on the site when they register. I know that the display name is located in the wp-users table of the database, but cant seam to be able to write to it.

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Edit

<?php

function wps_pro_login_registration_errors( $errors ) {
    if ( empty( $_POST['first_name'] ) )
        $errors->add( 'empty_first_name', '<strong>ERROR</strong>: Please enter your first name.' );
    if ( empty( $_POST['last_name'] ) )
        $errors->add( 'empty_last_name', '<strong>ERROR</strong>: Please enter your last name.' );
    if ( empty( $_POST['nickname'] ) )
        $errors->add( 'empty_nickname', '<strong>ERROR</strong>: Please enter your display name.' );
    return $errors;
}
add_filter( 'registration_errors', 'wps_pro_login_registration_errors' );
function wps_pro_login_user_register( $user_id )
{
    if (!empty($_POST['first_name']))
        update_user_meta($user_id, 'first_name', $_POST['first_name']);
    if (!empty($_POST['last_name']))
        update_user_meta($user_id, 'last_name', $_POST['last_name']);
    if ( !empty( $_POST['nickname'] ) )
        update_user_meta( $user_id, 'nickname', $_POST['nickname'] );
}
add_action( 'user_register', 'wps_pro_login_user_register' );

?>

This works fine to write to wp_usermeta table but since the display name is in the wp_users table it does not work.

I've added the following with no success.

if ( empty( $_POST['displayname'] ) )
        $errors->add( 'empty_displayname', '<strong>ERROR</strong>: Please enter your display name.' );

in the upper section and the following in the lower section

if ( !empty( $_POST['displayname'] ) )
        update_user_meta( $user_id, 'displayname', $_POST['displayname'] );

Answer 1

You need to use wp_update_user function to update user info. Please see below code:

<?php

$user_id = 1; /* It would be dynamic in your case */

$display_name = $_POST['display_name'];

$user_id = wp_update_user( array( 'ID' => $user_id, 'display_name' => $display_name ) );

if ( is_wp_error( $user_id ) ) {
    // There was an error, probably that user doesn't exist.
} else {
    // Success!
}

?>