downloads | documentation | faq | getting help | mailing lists | licenses | wiki | reporting bugs | php.net sites | links | conferences | my php.net

search for in the

List of Parser Tokens> <Unix Domain: Unix and UDG
[edit] Last updated: Fri, 22 Jul 2011

view this page in

PHP type comparison tables

The following tables demonstrate behaviors of PHP types and comparison operators, for both loose and strict comparisons. This supplemental is also related to the manual section on type juggling. Inspiration was provided by various user comments and by the work over at » BlueShoes.

Before utilizing these tables, it's important to understand types and their meanings. For example, "42" is a string while 42 is an integer. FALSE is a boolean while "false" is a string.

Note:

HTML Forms do not pass integers, floats, or booleans; they pass strings. To find out if a string is numeric, you may use is_numeric().

Note:

Simply doing if ($x) while $x is undefined will generate an error of level E_NOTICE. Instead, consider using empty() or isset() and/or initialize your variables.

Note:

Some numeric operations can result in a value represented by the constant NAN. Any loose or strict comparisons of this value against any other value, including itself, will have a result of FALSE. (i.e. NAN != NAN and NAN !== NAN) Examples of operations that produce NAN include sqrt(-1), asin(2), and asinh(0).

Comparisons of $x with PHP functions
Expression gettype() empty() is_null() isset() boolean : if($x)
$x = ""; string TRUE FALSE TRUE FALSE
$x = null NULL TRUE TRUE FALSE FALSE
var $x; NULL TRUE TRUE FALSE FALSE
$x is undefined NULL TRUE TRUE FALSE FALSE
$x = array(); array TRUE FALSE TRUE FALSE
$x = false; boolean TRUE FALSE TRUE FALSE
$x = true; boolean FALSE FALSE TRUE TRUE
$x = 1; integer FALSE FALSE TRUE TRUE
$x = 42; integer FALSE FALSE TRUE TRUE
$x = 0; integer TRUE FALSE TRUE FALSE
$x = -1; integer FALSE FALSE TRUE TRUE
$x = "1"; string FALSE FALSE TRUE TRUE
$x = "0"; string TRUE FALSE TRUE FALSE
$x = "-1"; string FALSE FALSE TRUE TRUE
$x = "php"; string FALSE FALSE TRUE TRUE
$x = "true"; string FALSE FALSE TRUE TRUE
$x = "false"; string FALSE FALSE TRUE TRUE

Loose comparisons with ==
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
TRUE TRUE FALSE TRUE FALSE TRUE TRUE FALSE TRUE FALSE FALSE TRUE FALSE
FALSE FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE TRUE FALSE TRUE
1 TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE TRUE FALSE TRUE TRUE
-1 TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
"1" TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE TRUE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" TRUE FALSE FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE TRUE FALSE TRUE
array() FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE TRUE FALSE FALSE
"php" TRUE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE

Strict comparisons with ===
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
TRUE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
1 FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
0 FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
-1 FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
"1" FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE
"0" FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE FALSE
"-1" FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE
NULL FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE FALSE
array() FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE FALSE
"php" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE FALSE
"" FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE TRUE



List of Parser Tokens> <Unix Domain: Unix and UDG
[edit] Last updated: Fri, 22 Jul 2011
 
add a note add a note User Contributed Notes PHP type comparison tables
Jouriy LYSENKO 17-Jun-2011 09:18
If $var not declared.

In php 5.2 :
<?php if($var) ?> - work

in php 5.3 :
<?php if($var) ?> - dont work and generate error E_NOTICE
mauritsdajong at gmail dot com 18-Feb-2011 03:12
When we're doing loose comparisons (with double equals signs), the following fact is interesting.

false == array() evaluates to true
false == "" evaluates to true
array() == "" however, evaluates to false
php at benizi dot com 15-Feb-2010 06:31
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
edgar at goodforall dot eu 15-Dec-2009 02:55
Some function to write out your own comparisson table in tsv format. Can be easily modified to add more testcases and/or binary functions. It will test all comparables against each other with all functions.

<?php
$funcs
= array(
       
/* Testing equality */
       
'eq' => '==',
       
'ne' => '!=',
       
'gt' => '>',
       
'lt' => '<',
       
'ne2' => '<>',
       
'lte' => '<=',
       
'gte' => '>=',
       
/* Testing identity */
       
'id' => '===',
       
'nid' => '!=='
);
class
Test {
        protected
$a;
        public
$b;
        public function
__construct($a,$b){
               
$this->a = $a;
               
$this->b = $b;
        }
        public function
getab(){
                return
$this->a.",". $this->b;
        }

}
$tst1 = new Test(1,2);
$tst2 = new Test(1,2);
$tst3 = new Test(2,2);
$tst4 = new Test(1,1);

$arr1 = array(1,2,3);
$arr2 = array(2,3,4);
$arr3 = array('a','b','c','d');
$arr4 = array('a','b','c');
$arr5 = array();

$comp1 = array(
       
'ints' => array(-1,0,1,2),
       
'floats' => array(-1.1,0.0,1.1,2.0),
       
'string' => array('str', 'str1', '', '1'),
       
'bools' => array(true, false),
       
'null' => array(null),
       
'objects' => array($tst1,$tst2,$tst3,$tst4),
       
'arrays' => array($arr1, $arr2, $arr3, $arr4, $arr5)
);
$fbody = array();

foreach(
$funcs as $name => $op){
       
$fbody[$name] = create_function('$a,$b', 'return $a ' . $op . ' $b;');
}

$table = array(array('function', 'comp1', 'comp2', 'f comp1 comp2', 'type'));
/* Do comparisons */
$comp2  = array();
foreach(
$comp1 as $type => $val){
       
$comp2[$type] = $val;
}

foreach(
$comp1 as $key1 => $val1){
        foreach(
$comp2 as $key2 => $val2){
               
addTableEntry($key1, $key2, $val1, $val2);
        }
}
$out = '';
foreach(
$table as $row){
       
$out .= sprintf("%-20s\t%-20s\t%-20s\t%-20s\t%-20s\n", $row[0], $row[1], $row[2], $row[3], $row[4]);
}

print
$out;
exit;

function
addTableEntry($n1, $n2, $comp1, $comp2){
        global
$table, $fbody;
        foreach(
$fbody as $fname => $func){
                        foreach(
$comp1 as $val1){
  foreach(
$comp2 as $val2){
                                       
$val = $func($val1,$val2);
                                               
$table[] = array($fname, gettype($val1) . ' => ' . sprintval($val1), gettype($val2) .' => ' . sprintval($val2), gettype($val) . ' => ' . sprintval($val), gettype($val1) . "-" . gettype($val2) . '-' . $fname);
                                        }
                        }
        }
}

function
sprintval($val){
        if(
is_object($val)){
                return
'object-' . $val->getab();
        }
        if(
is_array($val)){
                return
implode(',', $val);
        }
        if(
is_bool($val)){
                if(
$val){
                        return
'true';
                }
                return
'false';
        }
        return
strval($val);
}

?>
rich 08-May-2008 02:20
The note about object comparison should be corrected. Cloning objects does not imply instances are the same, so === would return FALSE.

Compare object
<?php
$o
= new stdClass();
$o->we = 12;

$o2 = new stdClass();
$o2->we = 12;

$o3 = clone $o2;
var_dump($o == $o2); //true
var_dump($o === $o2); //false
var_dump($o3 === $o2); //false
?>
gernovich at ya dot ru 08-May-2008 07:48
Universal comparison test.

<?php

$tests
= array();
$tests['==']  = create_function('$a, $b', 'return $a==$b;');
$tests['==='] = create_function('$a, $b', 'return $a===$b;');
$tests['!='] = create_function('$a, $b', 'return $a!=$b;');
$tests['<>'] = create_function('$a, $b', 'return $a<>$b;');
$tests['!=='] = create_function('$a, $b', 'return $a!==$b;');
$tests['<']   = create_function('$a, $b', 'return $a<$b;');
$tests['>']   = create_function('$a, $b', 'return $a>$b;');
$tests['<=']  = create_function('$a, $b', 'return $a<=$b;');
$tests['>=']  = create_function('$a, $b', 'return $a>=$b;');

$comparison = array();
$comparison['TRUE'] = true;
$comparison['FALSE'] = false;
$comparison['1'] = 1;
$comparison['0'] = 0;
$comparison['-1'] = -1;
$comparison['3,14'] = pi();
$comparison['"1"'] = '1';
$comparison['"0"'] = '0';
$comparison['"-1"'] = '-1';
$comparison['NULL'] = null;
$comparison['array()'] = array();
$comparison['"php"'] = 'php';
       
print
'<h1>PHP version '.PHP_VERSION.' type comparison tables</h1>';
       
foreach (
$tests as $test=>$function) {
    print
"<h2>Comparisons with $test</h2>";
    print
"<table border='1'>";
    print
"<tr>";
    print
"<th>&nbsp;</th>";
    foreach (
array_keys($comparison) as $name) {
        print
"<th>$name</th>";
    }
    print
"</tr>";
    foreach (
$comparison as $arg_1_name => $arg_1_value) {
        print
'<tr>';
        print
"<th>$arg_1_name</th>";
        foreach (
$comparison as $arg_2_value) {
            print
'<td>';
            print
$function($arg_1_value, $arg_2_value)==true ?
                       
'<span style="color:#00F;">TRUE</span>' : '<span style="color:#F00;">FALSE</span>';
            print
'</td>';
        }
        print
"</tr>";
    }
    print
"</table>";
}

?>
info at shaelf dot ru 06-Jan-2008 09:51
Compare object
<?php
$o
= new stdClass();
$o->we = 12;

$o2 = new stdClass();
$o2->we = 12;

$o3 = clone $o2;
var_dump($o == $o2); //true
var_dump($o === $o2); //false
var_dump($o3 === $o2); //true
?>
frank 14-Aug-2007 10:06
A comparison table for <=,<,=>,> would be nice...
Following are TRUE (tested PHP4&5):
NULL <= -1
NULL <= 0
NULL <= 1
!(NULL >= -1)
NULL >= 0
!(NULL >= 1)
That was a surprise for me (and it is not like SQL, I would like to have the option to have SQL semantics with NULL...).
15-Mar-2007 10:06
Re: omit's comment

The note omit quotes is referring to the VALUE returned, not its name. If you put 42 into a text field, the corresponding array value will be the string "42". The note makes no comment on the array's keys.
omit 23-Aug-2006 06:32
the manual said "HTML Forms do not pass integers, floats, or booleans; they pass strings"

while this is true, php will sometimes change the type to either type array, or possibly type integer(no, not a numeric string) if it was used as an array key. php seems to do this when it parses the request data into the predefined variable arrays.

example:

<input type="text" name="foo[5]">
<input type="text" name="foo[7]">

now obviously the browser will send those names as a string. but php will change thier type.

<?php

// $_POST['foo'] is an array
var_dump($_POST['foo']);

foreach (
$_POST['foo'] as $key => $val) {
   
// the keys 5 and 7 will be type integer
   
var_dump($key);
}

?>

because of this, its also a good idea to check the types of your variables.
Jan 29-Dec-2005 07:23
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
jerryschwartz at comfortable dot com 26-Jul-2005 08:04
In some languages, a boolean is promoted to an integer (with a value of 1 or -1, typically) if used in an expression with an integer. I found that PHP has it both ways:

If you add a boolean with a value of true to an integer with a value of 3, the result will be 4 (because the boolean is cast as an integer).

On the other hand, if you test a boolean with a value of true for equality with an integer with a value of three, the result will be true (because the integer is cast as a boolean).

Surprisingly, at first glance, if you use either < or > as the comparison operator the result is always false (again, because the integer as cast as a boolean, and true is neither greater nor less than true).
tom 17-Jun-2005 09:27
<?php
if (strlen($_POST['var']) > 0) {
   
// form value is ok
}
?>

When working with HTML forms this a good way to:

(A) let "0" post values through like select or radio values that correspond to array keys or checkbox booleans that would return FALSE with empty(), and;
(B) screen out $x = "" values, that would return TRUE with isset()!

Because HTML forms post values as strings, this is a good way to test variables!

[[Editor Note: This will create a PHP Error of level E_NOTICE if the checked variable (in this case $_POST['var']) is undefined. It may be used after (in conjuection with) isset() to prevent this.]]
aidan at php dot net 24-Jan-2005 03:00
The way PHP handles comparisons when multiple types are concerned is quite confusing.

For example:
"php" == 0

This is true, because the string is casted interally to an integer. Any string (that does not start with a number), when casted to an integer, will be 0.

 
show source | credits | sitemap | contact | advertising | mirror sites