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

Коментарии

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).
2005-07-26 16:04:32
http://php5.kiev.ua/manual/ru/types.comparisons.html
Автор:
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
2005-12-29 13:23:21
http://php5.kiev.ua/manual/ru/types.comparisons.html
Автор:
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...).
2007-08-14 18:06:35
http://php5.kiev.ua/manual/ru/types.comparisons.html
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;
               
$this->$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(truefalse),
       
'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);
                                               
$table[] = array($fnamegettype($val1) . ' => ' sprintval($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);
}

?>
2009-12-15 08:55:54
http://php5.kiev.ua/manual/ru/types.comparisons.html
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
2010-02-15 12:31:09
http://php5.kiev.ua/manual/ru/types.comparisons.html
The truth tables really ought to be colorized; they're very hard to read as they are right now (just big arrays of TRUE and FALSE).

Also, something to consider: clustering the values which compare similarly (like is done on qntm.org/equality) would make the table easier to read as well. (This can be done simply by hand by rearranging the order of headings to bring related values closer together).
2014-09-07 05:29:39
http://php5.kiev.ua/manual/ru/types.comparisons.html
There is also 0.0 which is not identical to 0.

  $x = 0.0; 
  gettype($x); // double
  empty($x); // true
  is_null($x); //false
  isset($x); // true
  is_numeric($x); // true
  $x ? true : false; // false
  $x == 0; // true
  $x == "0"; // true
  $x == "0.0"; // true
  $x == false; // true
  $x == null; // true
  $x === 0; // false
  $x === false; // false
  $x === null; // false
  $x === "0"; // false
  $x === "0.0"; // false
2018-03-29 23:59:47
http://php5.kiev.ua/manual/ru/types.comparisons.html
Автор:
Be aware of the difference between checking the *value* of an array item, and checking the *existence* of an array item:
<?php
$arr 
= [ 
 
'x' => 0,
 
'y' => null,
];

isset(
$arr['x']); // true, same as isset(0)
isset($arr['y']); // false, same as isset(null)

array_key_exists('y'$arr); // true, though the value is null
array_key_exists('z'$arr); // false
2023-07-14 19:26:54
http://php5.kiev.ua/manual/ru/types.comparisons.html

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