Tabelle zu Typenvergleichen in PHP

Die folgenden Tabellen zeigen das Verhalten von Typen und Vergleichsoperatoren in PHP, sowohl für schwach und stark typisierte Vergleiche. Dieser Anhang steht im Zusammenhang mit dem Abschnitt zu Type juggling. Anregungen für diesen Abschnitt kamen aus verschiedenen Benutzerkommentaren und der Arbeit von » BlueShoes.

Bevor diese Tabellen verwendet werden ist es wichtig die Typen und ihre Bedeutungen zu verstehen. "42" ist zum Beispiel ein string, während 42 ein int ist. false ist ein bool, obwohl "false" ein string ist.

Hinweis:

HTML-Formulare übergeben keine integer, float oder boolesche Werte, sie übertragen strings. Um herauszufinden, ob ein string numerisch ist kann man is_numeric() verwenden.

Hinweis:

Wenn man einfach if ($x) verwendet, obwohl $x undefiniert ist, so wird ein Fehler der Stufe E_NOTICE erzeugt. Verwenden sie stattdessen empty() oder isset() und/oder initialisiere sie die verwendeten Variablen.

Hinweis:

Einige numerische Operationen können ein Ergebnis erzeugen, welches durch die Konstante NAN represäntiert wird. Jeder schwach oder stark typisierte Vergleich dieses Wertes mit beliebigen anderen Werten, einschließlich der Konstante selbst, außer mit true, wird false ergeben (d.h. NAN != NAN und NAN !== NAN). Beispiele für Operationen, die NAN ergeben sind u.a. sqrt(-1), asin(2), und acosh(0).

Vergleiche von $x mittels PHP-Funktionen
Ausdruck gettype() empty() is_null() isset() bool : if($x)
$x = ""; string true false true false
$x = null; NULL true true false false
var $x; NULL true true false false
$x ist undefiniert 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; int false false true true
$x = 42; int false false true true
$x = 0; int true false true false
$x = -1; int 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

Typschwache Vergleiche mittels ==
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
* vor PHP 8.0.0 true.

Typstarke Vergleiche mittels ===
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 add a note

User Contributed Notes 23 notes

up
83
php at richardneill dot org
11 years ago
[Editor's note: As of PHP 5.4.4 this is no longer true. Integral strings that overflow into floating point numbers will no longer be considered equal.]

Be wary of string-comparison where both strings might be interpreted as numbers.  Eg:

$x="123456789012345678901234567890"; $y="123456789012345678900000000000";
echo  ($x==$y)?"equal":"not_equal";   #Prints equal !!

Both strings are getting converted to floats, then losing precision, then becoming equal :-(

Using "===" or making either of the strings non-numeric will prevent this.
[This is on a 32-bit machine, on a 64-bit, you will have to make the strings longer to see the effect]
up
47
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
25
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
18
aidan at php dot net
19 years ago
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.
up
17
Jan
18 years ago
Note that php comparison is not transitive:

"php" == 0 => true
0 == null => true
null == "php" => false
up
6
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
6
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
TrickyFoxy
4 years ago
<?php
echo md5('240610708') == md5('QNKCDZO') ? "equal" : "not equal"; // prints equal!!!
up
2
alt dot jl-3gi8b7l at binich dot com
6 years ago
Here's how PHP handles loose and strict comparisons of default parameters in functions:

Very unintuitive:

<?php
function f($x='surprise')
    {
    if (
$x == 'surprise')
        return
$x; // returns 0 !!
   
}
   
echo
f(0);
?>

Here some further tests:

<?php
function f($x='surprise')
    {
    if (
$x == 'surprise')
        return
'A:'.$x;
    if (
$x === 'surprise')
        return
'B:'.$x;
    return
'C:'.$x;
    }
   
echo
"\n".f(0); // A:0 !!
echo "\n".f(0.0); // A:0 !!
echo "\n".f(NULL); // C: !!
echo "\n".f(FALSE); // C:
echo "\n".f(); // A:surprise
echo "\n".f(''); // C:
echo "\n".f((integer)0); // A:0
echo "\n".f((string)0); // C:0
echo "\n".f('0'); // C:0
echo "\n".f(0.1); // C:0.1
echo "\n".f(array()); // C:Array
echo "\n".f('surprise'); // A:surprise
?>
up
1
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
0
trexx68
8 years ago
If you want to view the truth tables colorized, just:

1. Save a local copy of this page as an .html file,
2. View the page source with any text editor.
3. Replace the opening <head> tag so it will include this:

<head>
  <script src="https://code.jquery.com/jquery-1.10.2.js"></script>

4. Replace the closing </body> tag with this:

  <script>
    $( "td:contains('FALSE')" ).css("color", "red");
    $( "td:contains('TRUE')" ).css("color", "green");
  </script>
</body>

5. Save the file, and view it on your browser.  Enjoy.
up
-4
crazy888s at hotmail dot com
11 years ago
PHP's loose comparisons can be a huge convenience when used properly! It's extremely helpful to just remember the following are always FALSE:

null, false, "", 0, "0", array()

If your application never depends on a particular "empty/false/null/0/not set" value type, you won't have to worry about 99% of the other weird cases listed here. You won't need empty() or isset(). And ALL variable types will always work as expected for statements like:

if(boolean && !string){...}
if(array){...}
if(!null || int){...}

Consider the same when working with your database values.
up
-5
Anonymous
10 years ago
I'm running PHP 5.5.3.

This is a correction to one of the previous posts.

<?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
?>

Output is:

true, false, false
up
-4
info at shaelf dot ru
16 years ago
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
?>
up
-5
Anonymous
9 years ago
The loose comparison chart is missing a few things.

array(1)==true returns true.

also:

(int)array(1) === 1 returns true

This is symmetric:

array(1) === (array)1 returns true

but the loose comparison

array(1)==1 still returns false.
up
-5
aravind dot a dot padmanabhan at gmail dot com
8 years ago
please note that

$x = 0.0 ;
print empty($x); // returns 1 (true)

$x = "0.0";
print empty($x); // returns blank (false);
up
-2
php at ckls dot net
5 years ago
regarding the editors note in php at richardneill dot org note:
[Editor's note: As of PHP 5.4.4 this is no longer true. Integral strings that overflow into floating point numbers will no longer be considered equal.]

While this is true, there is still the following behaviour:
<?php
$x
= "1";
$y = "+1";
var_dump($x == $x);
?>
outputs "bool(true)". 
So still be wary of string-comparison where both strings might be interpreted as numbers.
up
-2
mark at theanti dot social
5 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
-2
biziclop at vipmail dot hu
6 years ago
Want to strictly compare integers that may or may not be converted to floats (via PHPExcel import/export, etc.)? You are out of luck:

var_dump(   (int)1 ===   (int)1 ); // bool(true)
var_dump( (float)1 === (float)1 ); // bool(true)
var_dump( (float)1 ===   (int)1 ); // bool(false)
var_dump(   (int)1 === (float)1 ); // bool(false)

This slightly complicated function might help you:

function equal_numbers( $a, $b ){
  if( $a === $b )  return true;
  if(   is_int( $a ) && is_float( $b ))  return (float)$a === $b && $a ===   (int)$b;
  if( is_float( $a ) &&   is_int( $b ))  return   (int)$a === $b && $a === (float)$b;
  return false;
}

Here are some tests:

test(100, 100.0 ); // int(100) float(100) bool(true)
test(  0,  -0   ); // int(0)   int(0)     bool(true)
test( -0,  -0.0 ); // int(0)   float(-0)  bool(true)
test(  0, 1/0   ); // int(0)   float(INF) bool(false)
test(  0, acos(2));// int(0)   float(NAN) bool(false)
test(       PHP_INT_MAX * 10, 0 );             //float(92233720368547758080) int(0) bool(false)
test((float)PHP_INT_MAX,     PHP_INT_MAX     );//float(9223372036854775808)  int(9223372036854775807) bool(false)
test((float)PHP_INT_MAX / 2, PHP_INT_MAX / 2 );//float(4611686018427387904)  float(4611686018427387904) bool(true)

function test( $a, $b ){
  var_dump( $a, $b, equal_numbers( $a, $b ));
}
up
-1
Anonymous
3 years ago
I noticed that some "magic" also happens when comparing strings with leading zeros with only two equal signs:

<?php
var_dump
('1' == '01');
var_dump('01' == '000001');
?>

Output:
bool(true)
bool(true)

If the string contains only numbers all leading zeroes seem to be ignored.
up
-12
Jouriy LYSENKO
12 years ago
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
up
-9
engineer dot morozov at gmail dot com
8 years ago
If you want to calculate how much more/less items by the criterion

Example:

in loop:
$counter += intval($item->isValid()) <=> 0.5;

if $counter >= 0 - valid items are more then invalid on $counter
if $counter  < 0 - valid items are less then invalid on $counter
up
-20
tom
18 years ago
<?php
if (strlen($_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.]]
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