It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
Die folgenden Tabellen zeigen das Verhalten von Typen und Vergleichsoperatoren in PHP, sowohl für schwach und stark typisierte Vergleiche. Dieser Anhang steht im Zusammenhang mit dem Abschnitt zu Type juggling. Anregungen für diesen Abschnitt kamen aus verschiedenen Benutzerkommentaren und der Arbeit von » BlueShoes.
Bevor diese Tabellen verwendet werden ist es wichtig die Typen und ihre
Bedeutungen zu verstehen. "42"
ist zum Beispiel ein
string, während 42
ein int
ist. false
ist ein bool, obwohl
"false"
ein string ist.
Hinweis:
HTML-Formulare übergeben keine integer, float oder boolesche Werte, sie übertragen strings. Um herauszufinden, ob ein string numerisch ist kann man is_numeric() verwenden.
Hinweis:
Wenn man einfach
if ($x)
verwendet, obwohl $x undefiniert ist, so wird ein Fehler der StufeE_NOTICE
erzeugt. Verwenden sie stattdessen empty() oder isset() und/oder initialisiere sie die verwendeten Variablen.
Hinweis:
Einige numerische Operationen können ein Ergebnis erzeugen, welches durch die Konstante
NAN
represäntiert wird. Jeder schwach oder stark typisierte Vergleich dieses Wertes mit beliebigen anderen Werten, einschließlich der Konstante selbst, außer mittrue
, wirdfalse
ergeben (d.h.NAN != NAN
undNAN !== NAN
). Beispiele für Operationen, dieNAN
ergeben sind u.a.sqrt(-1)
,asin(2)
, undacosh(0)
.
Ausdruck | gettype() | empty() | is_null() | isset() | bool : if($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 |
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
.
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 |
It's interesting to note that 'empty()' and 'boolean : if($x)'
are paired as logical opposites, as are 'is_null()' and 'isset()'.
Note that php comparison is not transitive:
"php" == 0 => true
0 == null => true
null == "php" => false
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...).
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
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);
}
?>
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).
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).
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