How to access User meta data within a plugin

Question

I am trying to write a plugin. I have added an extra field in a registration form using the plugin successfully. I would like to check whether the value in the extra field matches any username already registered.

When I try to validate using the predefined usermeta functions. I get the below errors:

require( 'C:\wamp\www\cpa\wp-load.php' )
require_once( 'C:\wamp\www\cpa\wp-config.php' )
require_once( 'C:\wamp\www\cpa\wp-settings.php' )

I am able to do this in a theme template. But I would like to know how to access all the predefined functions of WordPress inside a plugin like we do in theme files.

Code:

//1. Add a new form element...

$referral_username = $_REQUEST['referral'];

add_action('register_form','myplugin_register_form');
function myplugin_register_form (){
    $referral_username = ( isset( $_POST['referral_username'] ) ) ? $_POST['referral_username']: '';
    ?>
    <p>
        <label for="referral_username"><?php _e('Referral Username','mydomain') ?><br />
            <input type="text" name="referral_username" id="referral_username" class="input" size="20"value="<?php echo $referral_username = $_REQUEST['referral']; ?>" size="25" />



            </label>
    </p>
    <?php
}

//2. Add validation. In this case, we make sure referral_username is required.
add_filter('registration_errors', 'myplugin_registration_errors', 10, 3);
function myplugin_registration_errors ($errors, $sanitized_user_login, $user_email) {

    if ( empty( $_POST['referral_username'] ) )
        $errors->add( 'referral_username_error', __('<strong>ERROR</strong>: You must include a Valid Referral User Name. Else leave it blank.','mydomain') );

    return $errors;
}

//3. Finally, save our extra registration user meta.
add_action('user_register', 'myplugin_user_register');
function myplugin_user_register ($user_id) {
    if ( isset( $_POST['referral_username'] ) )
        update_user_meta($user_id, 'referral_username', $_POST['referral_username']);
}


//Test Usermeta

$user = get_userdatabylogin('vijay');
echo $user->ID; // prints the id of the user;

Answer 1

Please look at the last two lines of code. I am trying to print the id of the user. It works when used in the theme files but not inside the plugin.

//Test Usermeta

$user = get_userdatabylogin('vijay');
echo $user->ID; // prints the id of the user;

In PHP, you cannot (normally) execute a user function before it has been defined.

The plugin is executing the get_userdatabylogin() code before get_userdatabylogin() has been defined as a function.

The theme is executing the get_userdatabylogin() code after get_userdatabylogin() has been defined as a function.

Consult the Plugin API (or a WP Hooks database or search the WordPress code) to find the correct action name. Since you already know the code works in the theme, you should be able to use the after_setup_theme action to run your code.

add_action( 'after_setup_theme', 'test_user_meta' );
/**
 * Test User meta.
 */
function test_user_meta() {
    $user = get_userdatabylogin('vijay');
    echo $user->ID; // prints the id of the user;
}

Answer 2

Try adding this to the top of the plugin file and re-test:

require (ABSPATH . WPINC . '/pluggable.php');