PHP 8.1.28 Released!

Comparaison de types en PHP

La table suivante résume les différents comportements de PHP avec les types et opérateurs de comparaison, stricte ou large. Cette table est aussi reliée au transtypage. Elle a été inspirée par différents commentaires d'utilisateurs, et par le travail fait chez » BlueShoes.

Avant d'utiliser ces tables, il est important de comprendre les types et leur signification. Par exemple, "42" est une chaîne de caractères, alors que 42 est un entier. false est bool alors que "false" est une chaîne de caractères.

Note:

Les formulaires HTML ne connaissent pas les entiers, nombres à virgules et autres booléens. Pour savoir si une structure est un entier, utilisez is_numeric().

Note:

La ligne if ($x) génère une erreur de niveau E_NOTICE lorsque $x est indéfini. Alternativement, utilisez plutôt les fonctions empty() ou isset(), ou encore, initialisez toutes vos variables.

Note:

Des opérations numériques peuvent donner une valeur représentée par la constante NAN. Toutes les comparaisons de cette valeur avec une autre valeur, y compris cette même valeur, à l'exception de true auront comme résultat false (i.e. NAN != NAN et NAN !== NAN). Exemples d'opérations qui produisent la valeur NAN : sqrt(-1), asin(2), et acosh(0).

Comparaisons de $x avec des fonctions PHP
Expression gettype() empty() is_null() isset() bool : if($x)
$x = ""; chaîne de caractères true false true false
$x = null; NULL true true false false
var $x; NULL true true false false
$x est indéfini NULL true true false false
$x = []; array true false true false
$x = ['a', 'b']; array false false true true
$x = false; bool true false true false
$x = true; bool false false true true
$x = 1; entier false false true true
$x = 42; entier false false true true
$x = 0; entier true false true false
$x = -1; entier false false true true
$x = "1"; chaîne de caractères false false true true
$x = "0"; chaîne de caractères true false true false
$x = "-1"; chaîne de caractères false false true true
$x = "php"; chaîne de caractères false false true true
$x = "true"; chaîne de caractères false false true true
$x = "false"; string false false true true

Comparaison large avec ==
true false 1 0 -1 "1" "0" "-1" null [] "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 false* false*
-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
[] false true false false false false false false true true false false
"php" true false false false* false false false false false false true false
"" false true false false* false false false false true false false true
* true antérieur à PHP 8.0.0.

Comparaison stricte avec ===
true false 1 0 -1 "1" "0" "-1" null [] "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
[] 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

add a note

User Contributed Notes 8 notes

up
52
php at benizi dot com
14 years ago
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
up
26
Jan
18 years ago
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
up
24
frank
16 years ago
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...).
up
8
blue dot hirano at gmail dot com
9 years ago
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).
up
9
edgar at goodforall dot eu
14 years ago
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);
}

?>
up
1
mark at theanti dot social
6 years ago
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
up
3
jerryschwartz at comfortable dot com
18 years ago
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).
up
0
Jeroen
8 months ago
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
To Top