username_exists() │ WP 2.0.0

Checks whether the given username (login) exists.

Checks the presence of the specified username (login) in the user's database. The search passes through the user_login field.

The function requires file:

require_once ABSPATH . WPINC . '/user.php';

For more information on this and similar theme functions, check out the Conditional Tags article in the Theme Developer Handbook.

Uses: get_user_by()
Hooks from the function

Return

Int|false. The user ID on success, false on failure.

Usage

username_exists( $username );
$username(string) (required)
The username to check for existence.

Examples

0

#1 Example of username verification when registering a new user: 

$username = $_POST['username'];
if ( username_exists( $username ) )
	echo 'Username is already in use!';
else
	echo 'You can use this username!';

Changelog

Since 2.0.0 Introduced.

Code of username_exists() WP 6.0.1

wp-includes/user.php 
function username_exists( $username ) {
	$user = get_user_by( 'login', $username );
	if ( $user ) {
		$user_id = $user->ID;
	} else {
		$user_id = false;
	}

	/**
	 * Filters whether the given username exists.
	 *
	 * @since 4.9.0
	 *
	 * @param int|false $user_id  The user ID associated with the username,
	 *                            or false if the username does not exist.
	 * @param string    $username The username to check for existence.
	 */
	return apply_filters( 'username_exists', $user_id, $username );
}

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