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PHP : Appendices : List of Reserved Words

Appendix M. List of Reserved Words

The following is a listing of predefined identifiers in PHP. None of the identifiers listed here should be used as identifiers in any of your scripts. These lists include keywords and predefined variable, constant, and class names. These lists are neither exhaustive or complete.

List of Keywords

These words have special meaning in PHP. Some of them represent things which look like functions, some look like constants, and so on--but they're not, really: they are language constructs. You cannot use any of the following words as constants, class names, function or method names. Using them as variable names is generally OK, but could lead to confusion.

Table M.1. PHP Keywords

and	or	xor	__FILE__	exception (PHP 5)
__LINE__	array()	as	break	case
class	const	continue	declare	default
die()	do	echo()	else	elseif
empty()	enddeclare	endfor	endforeach	endif
endswitch	endwhile	eval()	exit()	extends
for	foreach	function	global	if
include()	include_once()	isset()	list()	new
print()	require()	require_once()	return()	static
switch	unset()	use	var	while
__FUNCTION__	__CLASS__	__METHOD__	final (as of PHP 5)	php_user_filter (as of PHP 5)
interface (as of PHP 5)	implements (as of PHP 5)	extends	public (as of PHP 5)	private (as of PHP 5)
protected (as of PHP 5)	abstract (as of PHP 5)	clone (as of PHP 5)	try (as of PHP 5)	catch (as of PHP 5)
throw (as of PHP 5)	cfunction (PHP 4 only)	old_function (PHP 4 only)	this (as of PHP 5)	namespace (PHP 6 only)
import (PHP 6 only)	goto (PHP 6 only)

Code Examples / Notes » reserved

sr

[Editorial note: parent and self are reserved class names. Functions and constants with their names can be declared, but not userspace classes] true, false and null are not listed because they are globally-defined constants, not reserved words. No idea about parent or self, though.

01-nov-2006 12:42

Two things: 1. It would be nice for this list to differentiate those reserved words, which are language constructs used *with* parentheses (isset, unset, empty, eval, exit, die, ...) and those rather to be used *without* parentheses (all includes, echo, print, return, ...?) This would really help define some common coding styles... 2. Do you write NULL, TRUE, FALSE or null, true, false? (I find CAPITAL letters better, however typing them can be annoying so I stick with using all lowercase letters, but what's the standard?)

al dot barrett

The list also seems to be missing both "parent" and "self" as well.

londonx

Naming a PHP5 class "variant" (with a constructor called the same) and then making an instance of it using __autoload triggers an error which disappears as soon as the name is changed. This should mean that "variant" is also a reserved word.

10-jan-2006 11:41

I don't see the boolean constants 'true' and 'false' listed among the reserved words/keywords/constants.

wsapplegate

I also can't find the NULL keyword in the list. The `extends' keyword is mentioned twice, too.

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