get_user_id_from_string( string $string )

Source

File: wp-includes/ms-deprecated.php

function get_user_id_from_string( $string ) {
	_deprecated_function( __FUNCTION__, '3.6.0', 'get_user_by()' );

	if ( is_email( $string ) )
		$user = get_user_by( 'email', $string );
	elseif ( is_numeric( $string ) )
		return $string;
	else
		$user = get_user_by( 'login', $string );

	if ( $user )
		return $user->ID;
	return 0;
}