validate_username() │ WP 2.0.1

Checks the correctness of the username (username - login).

If the username contains invalid characters, the function will return false — check failed.

Allowed characters: a-z _ - space . @, i.e., Latin alphabet, digits, and _ - space . @.

Suitable for checking the login, but not the displayed name! Since the underlying function is sanitize_user() with the second parameter true, i.e., strict sanitization. For example, all Cyrillic characters will be removed.

Uses: sanitize_user()
Hooks from the function

Returns

bool. true if the name meets the standards, otherwise false.

Usage

if( ! validate_username( $username ) ){
	// incorrect login
}
$username(string) (required)
Username (login) to check.

Examples

#1 Validate the username and check if it exists in the DB.

If the username is valid and this user doesn't exist in the database, then register it.

<?php
	$username = $_POST['username'];
	$error = false;
	if( !validate_username( $username ) )
		$error = "Invalid username!";
	if ( !$error && username_exists( $username ) )
		$error = "This user already exists!";

	if( !$error ){
		// register
	}
?>

Changelog

Since 2.0.1 Introduced.
Since 4.4.0 Empty sanitized usernames are now considered invalid.

validate_username() code WP 7.1

wp-includes/user.php 
function validate_username( $username ) {
	$sanitized = sanitize_user( $username, true );
	$valid     = ( $sanitized === $username && ! empty( $sanitized ) );

	/**
	 * Filters whether the provided username is valid.
	 *
	 * @since 2.0.1
	 *
	 * @param bool   $valid    Whether given username is valid.
	 * @param string $username Username to check.
	 */
	return apply_filters( 'validate_username', $valid, $username );
}

Other