我使用以下代码向用户配置文件添加了一个自定义字段：

/*** Adding extra field to get the the user who creates the another user during ADD NEW USER ***/

<?php

function custom_user_profile_fields($user){
    if(is_object($user))
        $created_by = esc_attr( get_the_author_meta( \'created_by\', $user->ID ) );
    else
        $created_by = null;
    ?>
    <h3>Extra profile information</h3>
    <table class="form-table">
        <tr>
            <th><label for="created_by">Created By</label></th>
            <td>
                <input type="text" class="regular-text" name="created_by" value="<?php echo $created_by; ?>" id="created_by" /><br />
                <span class="description">The person who creates this user</span>
            </td>
        </tr>
    </table>
<?php
}
add_action( \'show_user_profile\', \'custom_user_profile_fields\' );
add_action( \'edit_user_profile\', \'custom_user_profile_fields\' );
add_action( "user_new_form", "custom_user_profile_fields" );

function save_custom_user_profile_fields($user_id){
    update_user_meta($user_id, \'created_by\', $_POST[\'created_by\']);
}
add_action(\'user_register\', \'save_custom_user_profile_fields\');
add_action(\'profile_update\', \'save_custom_user_profile_fields\');

?>

现在我看到一个领域created by 当我从管理面板创建新用户时，现在我想通过字段获取用户created_by

法典：https://codex.wordpress.org/Function_Reference/get_users

根据法典，应该是这样的：

<?php 
get_users( $args ); 
$args = array(  
        \'meta_key\'     => \'\',
        \'meta_value\'   => \'\',
    )   
$blogusers = get_users( $args );
// Array of stdClass objects.
foreach ( $blogusers as  $my_users ) {
    echo  $my_users. \'<br/>\';
}
?>

我尝试了多种选择meta_key 和meta_value但所有的返回都是空的。

什么是exact meta_key 和meta_value 对于我使用函数创建的字段custom_user_profile_fields ?

如何通过自定义字段获取用户created_by ?

$args = array(  
        \'meta_key\'     => \'created_by\',
        \'meta_value\'   => 123,
)

$args = array( 
  \'meta_query\' => array(
    array(
        \'key\' => \'created_by\',
        \'compare\' => \'EXISTS\',
    ),
  ) 
);
var_dump(get_users($args));