I couldn't find much info on stacking the new ternary operator, so I ran some tests:
<?php
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 1 ?: 0 ?: 3 ?: 2; //1
echo 2 ?: 1 ?: 0 ?: 3; //2
echo 3 ?: 2 ?: 1 ?: 0; //3
echo 0 ?: 1 ?: 2 ?: 3; //1
echo 0 ?: 0 ?: 2 ?: 3; //2
echo 0 ?: 0 ?: 0 ?: 3; //3
?>
It works just as expected, returning the first non-false value within a group of expressions.
Vergleichs-Operatoren
Vergleichs-Operatoren erlauben es – wie der Name schon sagt – zwei Werte zu vergleichen. Wenn Sie an Beispielen verschiedener auf Typen bezogener Vergleiche interessiert sind, können Sie sich die PHP Typvergleich-Tabellen anschauen.
| Beispiel | Name | Ergebnis |
|---|---|---|
| $a == $b | Gleich |
Gibt true zurück, wenn nach der Typumwandlung $a
gleich $b ist.
|
| $a === $b | Identisch |
Gibt true zurück, wenn $a gleich
$b ist und beide denselben Typ haben.
|
| $a != $b | Ungleich |
Gibt true zurück, wenn nach der Typumwandlung $a
nicht gleich $b ist.
|
| $a <> $b | Ungleich |
Gibt true zurück, wenn nach der Typumwandlung $a
nicht gleich $b ist.
|
| $a !== $b | Nicht identisch |
Gibt true zurück, wenn $a nicht gleich
$b ist, oder wenn beide nicht denselben Typ haben.
|
| $a < $b | Kleiner als |
Gibt true zurück, wenn $a kleiner als
$b ist.
|
| $a > $b | Größer als |
Gibt true zurück, wenn $a größer als
$b ist.
|
| $a <= $b | Kleiner oder gleich |
Gibt true zurück, wenn $a kleiner oder gleich
$b ist.
|
| $a >= $b | Größer oder gleich |
Gibt true zurück, wenn $a größer oder gleich
$b ist.
|
| $a <=> $b | Raumschiff | Eine Ganzzahl (int), die kleiner als, gleich oder größer als 0 ist, wenn $a kleiner als, gleich oder größer als $b ist. |
Falls beide Operanden
numerische Zeichenketten
sind oder ein Operand eine Zahl ist und der andere eine
numerische Zeichenkette,
dann wird der Vergleich numerisch durchgeführt. Diese Regel gilt ebenfalls
für die switch-Anweisung.
Die Typumwandlung wird nicht durchgeführt, wenn der Vergleichsoperator
=== oder !== ist, da hier sowohl der
Typ als auch der Wert verglichen werden.
Warnung
Vor PHP 8.0.0 wurde bei einem Vergleich einer Zeichenkette mit einer Zahl oder einer numerischen Zeichenkette die Zeichenkette vor dem Vergleich in eine Zahl umgewandelt und der Vergleich numerisch durchgeführt.
<?php
var_dump(0 == "a");
var_dump("1" == "01");
var_dump("10" == "1e1");
var_dump(100 == "1e2");
switch ("a") {
case 0:
echo "0";
break;
case "a":
echo "a";
break;
}
?>Das oben gezeigte Beispiel erzeugt mit PHP 7 folgende Ausgabe:
bool(true) bool(true) bool(true) bool(true) 0
Das oben gezeigte Beispiel erzeugt mit PHP 8 folgende Ausgabe:
bool(false) bool(true) bool(true) bool(true) a
<?php
// Ganzzahlen
echo 1 <=> 1; // 0
echo 1 <=> 2; // -1
echo 2 <=> 1; // 1
// Gleitkommazahlen
echo 1.5 <=> 1.5; // 0
echo 1.5 <=> 2.5; // -1
echo 2.5 <=> 1.5; // 1
// Zeichenketten
echo "a" <=> "a"; // 0
echo "a" <=> "b"; // -1
echo "b" <=> "a"; // 1
echo "a" <=> "aa"; // -1
echo "zz" <=> "aa"; // 1
// Arrays
echo [] <=> []; // 0
echo [1, 2, 3] <=> [1, 2, 3]; // 0
echo [1, 2, 3] <=> []; // 1
echo [1, 2, 3] <=> [1, 2, 1]; // 1
echo [1, 2, 3] <=> [1, 2, 4]; // -1
// Objekte
$a = (object) ["a" => "b"];
$b = (object) ["a" => "b"];
echo $a <=> $b; // 0
$a = (object) ["a" => "b"];
$b = (object) ["a" => "c"];
echo $a <=> $b; // -1
$a = (object) ["a" => "c"];
$b = (object) ["a" => "b"];
echo $a <=> $b; // 1
// nicht nur die Werte werden verglichen; die Schlüssel müssen übereinstimmen
$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo $a <=> $b; // 1
?>Für die verschiedenen Typen wird der Vergleich gemäß der folgenden Tabelle durchgeführt (in der angegebenen Reihenfolge).
| Typ des 1. Operanden | Typ des 2. Operanden | Ergebnis |
|---|---|---|
| null oder string | string |
Umwandlung von null nach "", dann numerischer oder lexikalischer
Vergleich
|
| bool oder null | anything |
Umwandlung beider Werte nach bool, dann false < true
|
| object | object | Eingebaute Klassen können eigene Vergleichsregeln definieren; verschiedene Klassen können nicht verglichen werden; für den Vergleich von Objekten derselben Klasse siehe Objektvergleiche |
| string, resource, int oder float | string, resource, int oder float | Umwandlung von Zeichenketten und Ressourcen in Zahlen, dann numerischer Vergleich |
| array | array | Das Array mit weniger Elementen ist kleiner; wird ein Schlüssel vom ersten Operanden nicht im zweiten gefunden, dann sind die Arrays nicht vergleichbar, andernfalls wird Element für Element verglichen (siehe folgendes Beispiel) |
| object | anything | object ist immer größer |
| array | anything | array ist immer größer |
Beispiel #1 Boolesche und null-Vergleiche
<?php
// Boolesche Werte und null werden immer als Boolesche Werte verglichen
var_dump(1 == TRUE); // TRUE - dasselbe wie (bool)1 == TRUE
var_dump(0 == FALSE); // TRUE - dasselbe wie (bool)0 == FALSE
var_dump(100 < TRUE); // FALSE - dasselbe wie (bool)100 < TRUE
var_dump(-10 < FALSE);// FALSE - dasselbe wie (bool)-10 < FALSE
var_dump(min(-100, -10, NULL, 10, 100)); // NULL - (bool)NULL < (bool)-100 ist FALSE < TRUE
?>
Beispiel #2 Umschreibung von Standard-Array-Vergleichen
<?php
// Arrays werden mit den normalen Vergleichsoperatoren sowie dem Raumschiff-Operator wie folgt verglichen
function standard_array_compare($op1, $op2)
{
if (count($op1) < count($op2)) {
return -1; // $op1 < $op2
} elseif (count($op1) > count($op2)) {
return 1; // $op1 > $op2
}
foreach ($op1 as $key => $val) {
if (!array_key_exists($key, $op2)) {
return 1;
} elseif ($val < $op2[$key]) {
return -1;
} elseif ($val > $op2[$key]) {
return 1;
}
}
return 0; // $op1 == $op2
}
?>Warnung
Vergleich von Gleitkommazahlen
Aufgrund der Art wie Gleitkommazahlen (float) intern dargestellt werden, sollten zwei Gleitkommazahlen nicht auf Gleichheit getestet werden.
Weitere Informationen sind der Dokumantation von float zu entnehmen.
Hinweis: Es ist wichtig zu beachten, dass die Typumwandlung von PHP nicht immer offensichtlich ist, wenn Werte unterschiedlichen Typs verglichen werden, insbesondere beim Vergleich von Integern mit Booleans oder Integern mit Strings. Daher ist es im Allgemeinen in den meisten Fällen ratsam,
===und!==für Vergleiche zu verwenden, anstatt==und!=.
Nicht vergleichbare Werte
Während der Identitätsvergleich (=== und
!==) auf beliebige Werte angewendet werden kann, sollten
die anderen Vergleichsoperatoren nur auf vergleichbare Werte angewandt
werden. Wenn nicht vergleichbare Werte verglichen werden, ist das Ergebnis
undefiniert und sollte nicht als verlässlich eingestuft werden.
Ternärer Operator
Ein weiterer Vergleichs-Operator ist der "?:" (oder ternäre) Operator.
Beispiel #3 Zuweisen eines Standardwerts
<?php
// Beispielanwendung für den ternären Operator
$action = (empty($_POST['action'])) ? 'standard' : $_POST['action'];
// Obiges ist mit dieser if/else-Anweisung identisch
if (empty($_POST['action'])) {
$action = 'standard';
} else {
$action = $_POST['action'];
}
?>(ausdr1) ? (ausdr2) : (ausdr3) wird zu
ausdr2 ausgewertet, wenn
ausdr1 als true ausgewertet wird, und zu
ausdr3, wenn ausdr1
zu false ausgewertet wird.
Beim ternären Operator kann der mittlere Teil weggelassen werden. Der
Ausdruck (ausdr1) ?: (ausdr3) wird zum Ergebnis von
ausdr1 zurück, wenn
ausdr1 zu true ausgewertet wird, und zu
ausdr3 andernfalls.
ausdr1 wird in diesem Fall nur einmal
ausgewertet.
Hinweis: Es ist zu beachten, dass der ternäre Operator ein Ausdruck ist und nicht als Variable, sondern als Wert eines Ausdrucks ausgewertet wird. Dies ist unbedingt zu berücksichtigen, wenn eine Variable per Referenz zurückgegeben werden soll. Die Anweisung
return $var == 42 ? $a : $b;in einer Funktion, die per Referenz zurückgibt, wird daher nicht funktionieren und eine Warnung erzeugen.
Hinweis:
Es wird empfohlen, die "Verschachtelung" von ternären Ausdrücken zu vermeiden. Das Verhalten von PHP bei der Verwendung von mehr als einem nicht einkgeklammerten ternären Operator innerhalb eines einzigen Ausdrucks ist im Vergleich zu anderen Sprachen nicht eindeutig. In der Tat wurden ternäre Ausdrücke vor PHP 8.0.0 links-assoziativ (von links nach rechts) ausgewertet, und nicht rechts-assoziativ wie in den meisten anderen Programmiersprachen. Die Links-Assoziativität ist seit PHP 7.4.0 veraltet. Seit PHP 8.0.0 ist der ternäre Operator nicht-assoziativ.
Beispiel #4 Ungewöhnliches Verhalten des ternären Operators
<?php
// auf den ersten Blick scheint das folgende 'true' auszugeben
echo (true ? 'true' : false ? 't' : 'f');
// allerdings wird vor PHP 8.0.0 tatsächlich 't' ausgegeben
// das kommt daher, dass ternäre Ausdrücke links-assoziativ ausgewertet werden
// das Folgende ist eine augenfälligere Variante desselben Codes wie oben
echo ((true ? 'true' : false) ? 't' : 'f');
// hier kann man sehen, dass der erste Ausdruck zu 'true' ausgewertet wird,
// was wiederum zu (bool)true ausgewertet wird, und daher wird der Wahr-Zweig
// des zweiten ternären Ausdrucks zurückgegeben.
?>
Hinweis:
Die Verkettung von kurzen ternären Operatoren (
?:) ist jedoch stabil und verhält sich plausibel. Sie wird zum ersten Argument ausgewertet, das einen nicht-falschen Wert ergibt. Es ist zu beachten, dass undefinierte Werte immer noch eine Warnung auslösen.Beispiel #5 Verkettung kurzer ternärer Operatoren
<?php
echo 0 ?: 1 ?: 2 ?: 3, PHP_EOL; //1
echo 0 ?: 0 ?: 2 ?: 3, PHP_EOL; //2
echo 0 ?: 0 ?: 0 ?: 3, PHP_EOL; //3
?>
Null-Koaleszens-Operator
Eine weitere nützliche Kurzform eines Operators ist der Operator "??" (null-Koaleszenz-Operator, etwa: Zuweisungsoperator für die Kombination mit null).
Beispiel #6 Zuweisung eines Standardwerts
<?php
// Beispiel für die Verwendung des null-Koaleszenz-Operators
$action = $_POST['action'] ?? 'standard';
// Obiges ist mit dieser if/else-Anweisung identisch
if (isset($_POST['action'])) {
$action = $_POST['action'];
} else {
$action = 'standard';
}
?>(ausdr1) ?? (ausdr2) wird zu
ausdr2 ausgewertet, wenn
ausdr1 null ist, und zu
ausdr1 andernfalls.
Insbesondere gibt dieser Operator keinen Hinweis und keine Warnung aus, wenn der Wert auf der linken Seite nicht existiert, genau wie isset(). Dies ist besonders für Array-Schlüssel nützlich.
Hinweis: Es ist zu beachten, dass der null-Koaleszenz-Operator ein Ausdruck ist und nicht als Variable, sondern als Wert eines Ausdrucks ausgewertet wird. Dies ist unbedingt zu berücksichtigen, wenn eine Variable per Referenz zurückgegeben werden soll. Die Anweisung
return $foo ?? $bar;in einer Funktion, die per Referenz zurückgibt, wird daher nicht funktionieren, und eine Warnung erzeugen.
Hinweis:
Der null-Koaleszenz-Operator hat eine niedrige Priorität. Das heißt, wenn er mit anderen Operatoren (z. B. Verkettung von Zeichenketten oder arithmetische Operatoren) kombiniert wird, sind wahrscheinlich Klammern erforderlich.
<?php
// Löst die Warnung aus, dass $name undefiniert ist.
print 'Mr. ' . $name ?? 'Anonymous';
// Gibt "Mr. Anonymous" aus
print 'Mr. ' . ($name ?? 'Anonymous');
?>
Hinweis:
Es ist zu beachten, dass der null-Koaleszenz-Operator einfach verschachtelt werden kann:
Beispiel #7 Verschachtelung des null-Koaleszenz-Operators
<?php
$foo = null;
$bar = null;
$baz = 1;
$qux = 2;
echo $foo ?? $bar ?? $baz ?? $qux; // gibt 1 aus
?>
add a note
User Contributed Notes 45 notes
crazy888s at hotmail dot com ¶
13 years ago
arnaud at arnapou dot net ¶
13 years ago
[Editor's note: consider using ===]
I discover after 10 years of PHP development something awfull : even if you make a string comparison (both are strings), strings are tested like integers and leading "space" character (even \n, \r, \t) is ignored ....
I spent hours because of leading \n in a string ... it hurts my developper sensibility to see two strings beeing compared like integers and not like strings ... I use strcmp now for string comparison ... so stupid ...
Test code :
<?php
test("1234", "1234");
test("1234", " 1234");
test("1234", "\n1234");
test("1234", "1234 ");
test("1234", "1234\n");
function test($v1, $v2) {
echo "<h1>[".show_cr($v1)."] vs [".show_cr($v2)."]</h1>";
echo my_var_dump($v1)."<br />";
echo my_var_dump($v2)."<br />";
if($v1 == $v2) {
echo "EQUAL !";
}
else {
echo "DIFFERENT !";
}
}
function show_cr($var) {
return str_replace("\n", "\\n", $var);
}
function my_var_dump($var) {
ob_start();
var_dump($var);
$dump = show_cr(trim(ob_get_contents()));
ob_end_clean();
return $dump;
}
?>
Displays this ->
[1234] vs [1234]
string(4) "1234"
string(4) "1234"
EQUAL !
[1234] vs [ 1234]
string(4) "1234"
string(5) " 1234"
EQUAL !
[1234] vs [\n1234]
string(4) "1234"
string(5) "\n1234"
EQUAL !
[1234] vs [1234 ]
string(4) "1234"
string(5) "1234 "
DIFFERENT !
[1234] vs [1234\n]
string(4) "1234"
string(5) "1234\n"
DIFFERENT !
Harry Willis ¶
9 years ago
I was interested about the following two uses of the ternary operator (PHP >= 5.3) for using a "default" value if a variable is not set or evaluates to false:
<?php
(isset($some_variable) && $some_variable) ? $some_variable : 'default_value';
$some_variable ?: 'default_value';
?>
The second is more readable, but will throw an ERR_NOTICE is $some_variable is not set. Of course, this could be overcome by suppressing the notice using the @ operator.
Performance-wise, though, comparing 1 million iterations of the three statements
(isset($foo) && $foo) ? $foo : ''
($foo) ?: ''
(@$foo) ?: ''
results in the following:
$foo is NOT SET.
[isset] 0.18222403526306
[?:] 0.57496404647827
[@ ?:] 0.64780592918396
$foo is NULL.
[isset] 0.17995285987854
[?:] 0.15304207801819
[@ ?:] 0.20394206047058
$foo is FALSE.
[isset] 0.19388508796692
[?:] 0.15359902381897
[@ ?:] 0.20741701126099
$foo is TRUE.
[isset] 0.17265486717224
[?:] 0.11773896217346
[@ ?:] 0.16193103790283
In other words, using the long-form ternary operator with isset($some_variable) is preferable overall if $some_variable may not be set.
(error_reporting was set to zero for the benchmark, to avoid printing a million notices...)
thomas dot oldbury at tgohome dot com ¶
16 years ago
Be careful when using the ternary operator!
The following will not evaluate to the expected result:
<?php
echo "a string that has a " . (true) ? 'true' : 'false' . " condition in. ";
?>
Will print true.
Instead, use this:
<?php
echo "a string that has a " . ((true) ? 'true' : 'false') . " condition in. ";
?>
This will evaluate to the expected result: "a string that has a true condition in. "
I hope this helps.
jwhiting at hampshire dot edu ¶
19 years ago
note: the behavior below is documented in the appendix K about type comparisons, but since it is somewhat buried i thought i should raise it here for people since it threw me for a loop until i figured it out completely.
just to clarify a tricky point about the == comparison operator when dealing with strings and numbers:
('some string' == 0) returns TRUE
however, ('123' == 0) returns FALSE
also note that ((int) 'some string') returns 0
and ((int) '123') returns 123
the behavior makes senes but you must be careful when comparing strings to numbers, e.g. when you're comparing a request variable which you expect to be numeric. its easy to fall into the trap of:
if ($_GET['myvar']==0) dosomething();
as this will dosomething() even when $_GET['myvar'] is 'some string' and clearly not the value 0
i was getting lazy with my types since php vars are so flexible, so be warned to pay attention to the details...
jeronimo at DELETE_THIS dot transartmedia dot com ¶
19 years ago
For converted Perl programmers: use strict comparison operators (===, !==) in place of string comparison operators (eq, ne). Don't use the simple equality operators (==, !=), because ($a == $b) will return TRUE in many situations where ($a eq $b) would return FALSE.
For instance...
"mary" == "fred" is FALSE, but
"+010" == "10.0" is TRUE (!)
In the following examples, none of the strings being compared are identical, but because PHP *can* evaluate them as numbers, it does so, and therefore finds them equal...
<?php
echo ("007" == "7" ? "EQUAL" : "not equal");
// Prints: EQUAL
// Surrounding the strings with single quotes (') instead of double
// quotes (") to ensure the contents aren't evaluated, and forcing
// string types has no effect.
echo ( (string)'0001' == (string)'+1.' ? "EQUAL" : "not equal");
// Prints: EQUAL
// Including non-digit characters (like leading spaces, "e", the plus
// or minus sign, period, ...) can still result in this behavior, if
// a string happens to be valid scientific notation.
echo (' 131e-2' == '001.3100' ? "EQUAL" : "not equal");
// Prints: EQUAL
?>
If you're comparing passwords (or anything else for which "near" precision isn't good enough) this confusion could be detrimental. Stick with strict comparisons...
<?php
// Same examples as above, using === instead of ==
echo ("007" === "7" ? "EQUAL" : "not equal");
// Prints: not equal
echo ( (string)'0001' === (string)'+1.' ? "EQUAL" : "not equal");
// Prints: not equal
echo (' 131e-2' === '001.3100' ? "EQUAL" : "not equal");
// Prints: not equal
?>
mail at mkharitonov dot net ¶
9 years ago
Be careful with the "==" operator when both operands are strings:
<?php
var_dump('123' == ' 123'); // true
var_dump('1e3' == '1000'); // true
var_dump('+74951112233' == '74951112233'); // true
var_dump('00000020' == '0000000000000000020'); // true
var_dump('0X1D' == '29E0'); // true
var_dump('0xafebac' == '11529132'); // true
var_dump('0xafebac' == '0XAFEBAC'); // true
var_dump('0xeb' == '+235e-0'); // true
var_dump('0.235' == '+.235'); // true
var_dump('0.2e-10' == '2.0E-11'); // true
var_dump('61529519452809720693702583126814' == '61529519452809720000000000000000'); // true in php < 5.4.4
hiroh2k at yahoo dot com ¶
19 years ago
if you want to use the ?: operator, you should be careful with the precedence.
Here's an example of the priority of operators:
<?php
echo 'Hello, ' . isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register';
?>
This make "'Hello, ' . isset($i)" the sentence to evaluate. So, if you think to mix more sentences with the ?: operator, please use always parentheses to force the proper evaluation of the sentence.
<?php
echo 'Hello, ' . (isset($i) ? 'my friend: ' . $username . ', how are you doing?' : 'my guest, ' . $guestusername . ', please register');
?>
for general rule, if you mix ?: with other sentences, always close it with parentheses.
Anonymous ¶
18 years ago
The following contrasts the trinary operator associativity in PHP and Java. The first test would work as expected in Java (evaluates left-to-right, associates right-to-left, like if stmnt), the second in PHP (evaluates and associates left-to-right)
<?php
echo "\n\n######----------- trinary operator associativity\n\n";
function trinaryTest($foo){
$bar = $foo > 20
? "greater than 20"
: $foo > 10
? "greater than 10"
: $foo > 5
? "greater than 5"
: "not worthy of consideration";
echo $foo." => ".$bar."\n";
}
echo "----trinaryTest\n\n";
trinaryTest(21);
trinaryTest(11);
trinaryTest(6);
trinaryTest(4);
function trinaryTestParens($foo){
$bar = $foo > 20
? "greater than 20"
: ($foo > 10
? "greater than 10"
: ($foo > 5
? "greater than 5"
: "not worthy of consideration"));
echo $foo." => ".$bar."\n";
}
echo "----trinaryTestParens\n\n";
trinaryTestParens(21);
trinaryTestParens(11);
trinaryTest(6);
trinaryTestParens(4);
?>
Output:
######----------- trinary operator associativity
----trinaryTest
21 => greater than 5
11 => greater than 5
6 => greater than 5
4 => not worthy of consideration
----trinaryTestParens
21 => greater than 20
11 => greater than 10
6 => greater than 5
4 => not worthy of consideration
kapoor_rajiv at hotmail dot com ¶
14 years ago
A quick way to do mysql bit comparison in php is to use the special character it stores . e.g
<?php
if ($AvailableRequests['OngoingService'] == '')
echo '<td>Yes</td>';
else
echo '<td>No</td>';
?>
rshawiii at yahoo dot com ¶
17 years ago
You can't just compare two arrays with the === operator
like you would think to find out if they are equal or not. This is more complicated when you have multi-dimensional arrays. Here is a recursive comparison function.
<?php
/**
* Compares two arrays to see if they contain the same values. Returns TRUE or FALSE.
* usefull for determining if a record or block of data was modified (perhaps by user input)
* prior to setting a "date_last_updated" or skipping updating the db in the case of no change.
*
* @param array $a1
* @param array $a2
* @return boolean
*/
function array_compare_recursive($a1, $a2)
{
if (!(is_array($a1) and (is_array($a2)))) { return FALSE;}
if (!count($a1) == count($a2))
{
return FALSE; // arrays don't have same number of entries
}
foreach ($a1 as $key => $val)
{
if (!array_key_exists($key, $a2))
{return FALSE; // uncomparable array keys don't match
}
elseif (is_array($val) and is_array($a2[$key])) // if both entries are arrays then compare recursive
{if (!array_compare_recursive($val,$a2[$key])) return FALSE;
}
elseif (!($val === $a2[$key])) // compare entries must be of same type.
{return FALSE;
}
}
return TRUE; // $a1 === $a2
}
?>
Jeremy Swinborne ¶
11 years ago
Beware of the consequences of comparing strings to numbers. You can disprove the laws of the universe.
echo ('X' == 0 && 'X' == true && 0 == false) ? 'true == false' : 'sanity prevails';
This will output 'true == false'. This stems from the use of the UNIX function strtod() to convert strings to numbers before comparing. Since 'X' or any other string without a number in it converts to 0 when compared to a number, 0 == 0 && 'X' == true && 0 == false
G ¶
6 years ago
Do note, using the ternary operator shorthand (since 5.3), omitting the 2nd expression the first expression will only be called once.
Before 5.3 (or not using the shorthand)
<?php
$val = f('x') ? f('x') : false;
// f('x') will be run twice
?>
After 5.3
<?php
$val = f('x') ?: false;
// f('x') will be run once
?>
gondo ¶
9 years ago
beware of the fact, that there is no `<==` nor `>==` therefore `false <= 0` will be `true`. php v. 5.4.27
Alex ¶
17 years ago
I think everybody should read carefully what "jeronimo at DELETE_THIS dot transartmedia dot com" wrote. It's a great pitfall even for seasoned programmers and should be looked upon with a great attention.
For example, comparing passwords with == may result in a very large security hole.
I would add some more to it:
The workaround is to use strcmp() or ===.
Note on ===:
While the php documentation says that, basically,
($a===$b) is the same as ($a==$b && gettype($a) == gettype($b)),
this is not true.
The difference between == and === is that === never does any type conversion. So, while, according to documentation, ("+0.1" === ".1") should return true (because both are strings and == returns true), === actually returns false (which is good).
niall at maranelda dot org ¶
6 years ago
Care must be taken when using the spaceship operator with arrays that do not have the same keys:
- Contrary to the notes above ("Example #2 Transcription of standard array comparison"), it does *not* return null if the left-hand array contains a key that the right-hand array does not.
- Because of this, the result depends on the order you do the comparison in.
For example:
<?php
$a = ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4];
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];
var_dump($a <=> $b); // int(1) : $a > $b because $a has the 'c' key and $b doesn't.
var_dump($b <=> $a); // int(1) : $b > $a because $b has the 'd' key and $a doesn't.
?>
adam at caucho dot com ¶
17 years ago
Note: according to the spec, PHP's comparison operators are not transitive. For example, the following are all true in PHP5:
"11" < "a" < 2 < "11"
As a result, the outcome of sorting an array depends on the order the elements appear in the pre-sort array. The following code will dump out two arrays with *different* orderings:
<?php
$a = array(2, "a", "11", 2);
$b = array(2, "11", "a", 2);
sort($a);
var_dump($a);
sort($b);
var_dump($b);
?>
This is not a bug report -- given the spec on this documentation page, what PHP does is "correct". But that may not be what was intended...
bishop ¶
17 years ago
When you want to know if two arrays contain the same values, regardless of the values' order, you cannot use "==" or "===". In other words:
<?php
(array(1,2) == array(2,1)) === false;
?>
To answer that question, use:
<?php
function array_equal($a, $b) {
return (is_array($a) && is_array($b) && array_diff($a, $b) === array_diff($b, $a));
}
?>
A related, but more strict problem, is if you need to ensure that two arrays contain the same key=>value pairs, regardless of the order of the pairs. In that case, use:
<?php
function array_identical($a, $b) {
return (is_array($a) && is_array($b) && array_diff_assoc($a, $b) === array_diff_assoc($b, $a));
}
?>
Example:
<?php
$a = array (2, 1);
$b = array (1, 2);
// true === array_equal($a, $b);
// false === array_identical($a, $b);
$a = array ('a' => 2, 'b' => 1);
$b = array ('b' => 1, 'a' => 2);
// true === array_identical($a, $b)
// true === array_equal($a, $b)
?>
(See also the solution "rshawiii at yahoo dot com" posted)
Cuong Huy To ¶
12 years ago
In the table "Comparison with Various Types", please move the last line about "Object" to be above the line about "Array", since Object is considered to be greater than Array (tested on 5.3.3)
(Please remove my "Anonymous" post of the same content before. You could check IP to see that I forgot to type my name)
stepheneliotdewey at gmail [period] com ¶
16 years ago
Note that typecasting will NOT prevent the default behavior for converting two numeric strings to numbers when comparing them.
e.g.:
<?php
if ((string) '0123' == (string) '123')
print 'equals';
else
print 'doesn\'t equal';
?>
Still prints 'equals'
As far as I can tell the only way to avoid this is to use the identity comparison operators (=== and !==).
itsacon at itsacon dot net ¶
2 years ago
Be aware that the null coalesce operator (??) has a lower priority than most other operators, so parentheses are usually a good idea if the output is used in anything other than an assignment.
<?php
$var = 1;
if ($var ?? 0 == 2) {} // will evaluate to true
if (2 == $undefinedVar ?? 0) {} // will throw an error
if (($var ?? 0) == 2) {} // will evaluate to false
?>
https://www.php.net/manual/en/language.operators.precedence.php
prezire at gmail dot com ¶
7 years ago
Take note when grouping ternary operations that return either boolean or integer concatenated to a string:
<?php
echo 'hello ' . true ? 1 : 0, //Outputs 1
'hello ' . (true ? 1 : 0); //Outputs hello 1
?>
Sumon Mahmud ¶
3 years ago
Extending from here: https://www.php.net/manual/en/language.operators.comparison.php#121907
$a = ['a' => 1, 'b' => 2, 'c' => 3, 'e' => 4];
$b = ['a' => 1, 'b' => 2, 'd' => 3, 'e' => 4];
echo $a > $b; // 0
echo $b > $a; // 0
echo $a <$b; // 0
echo $b < $a; // 0
If using spaceship operator then it is returning true like :
echo $a <=> $b; //1
echo $b <=> $a; //1
echo $a <=> $b; //1
echo $b <=> $a; //1
Anonymous ¶
14 years ago
Note: The ternary shortcut currently seems to be of no use in dealing with unexisting keys in an array, as PHP will throw an error. Take the following example.
<?php
$_POST['Unexisting'] = $_POST['Unexisting'] ?: false;
?>
PHP will throw an error that the "Unexisting" key does not exist. The @ operator does not work here to suppress this error.
bimal at sanjaal dot com ¶
10 years ago
I came across peculiar outputs while I was attempting to debug a script
<?php
# Setup platform (pre conditions somewhere in a loop)
$index=1;
$tally = array();
# May work with warnings that $tally[$index] is not initialized
# Notice: Undefined offset: 1 in D:\htdocs\colors\ColorCompare\i.php on line #__
# It is an old fashioned way.
# $tally[$index] = $tally[$index] + 1;
# Does not work: Loops to attempt to change $index and values are aways unaffected
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
$tally[$index] = isset($tally[$index])?$tally[$index]:0+1;
/*
# These three lines output:
Array
(
[1] => 1
)
*/
# Works: This is what I need/expect
# $tally[$index] = 1+(isset($tally[$index])?$tally[$index]:0);
print_r($tally);
?>
The second block obviously does not work what one expects.
Third part is good.
alan dot g at nospam dot net ¶
13 years ago
a function to help settings default values, it returns its own first non-empty argument :
make your own eor combos !
<?php
/*
* Either Or
*
* usage: $foo = eor(test1(),test2(),"default");
* usage: $foo = eor($_GET['foo'], foogen(), $foo, "bar");
*/
function eor() {
$vars = func_get_args();
while (!empty($vars) && empty($defval))
$defval = array_shift($vars);
return $defval;
}
?>
Hayley Watson ¶
16 years ago
Note that the "ternary operator" is better described as the "conditional operator". The former name merely notes that it has three arguments without saying anything about what it does. Needless to say, if PHP picked up any more ternary operators, this will be a problem.
"Conditional Operator" is actually descriptive of the semantics, and is the name historically given to it in, e.g., C.
fernandoleal at dragoncs dot com ¶
16 years ago
If you need nested ifs on I var its important to group the if so it works.
Example:
<?php
//Dont Works
//Parse error: parse error, unexpected ':'
$var='<option value="1" '.$status == "1" ? 'selected="selected"' :''.'>Value 1</option>';
//Works:
$var='<option value="1" '.($status == "1" ? 'selected="selected"' :'').'>Value 1</option>';
echo $var;
?>
Mark Simon ¶
12 years ago
The use of 5.3’s shortened ternary operator allows PHP to coalesce a null or empty value to an alternative:
$value = $planA ?: $planB;
My own server doesn’t yet run 5.3. A nice alternative is to use the “or” operator:
$value = $planA or $value = planB;
Marcin Kuzawiski ¶
8 years ago
A < B and still B < A...
$A = [1 => 1, 2 => 0, 3 => 1];
$B = [1 => 1, 3 => 0, 2 => 1];
var_dump($A < $B); // TRUE
var_dump($B < $A); // TRUE
var_dump($A > $B); // TRUE
var_dump($B > $A); // TRUE
Next - C and D are comparable, but neither C < D nor D < C (and still C != D)...
$C = [1 => 1, 2 => 1, 3 => 0];
$D = [1 => 1, 3 => 1, 2 => 0];
var_dump($C < $D); // FALSE
var_dump($D < $C); // FALSE
var_dump($C > $D); // FALSE
var_dump($D > $C); // FALSE
var_dump($D == $C); // FALSE
Romain ¶
5 years ago
?? vs isset() with __isset() and __get()
<?php
class A
{
public function __get($id)
{
return 'a value';
}
}
class B
{
public function __isset($id)
{
return false;
}
public function __get($id)
{
return 'a value';
}
}
class c
{
protected $test = "a value";
public function __isset($id)
{
return true;
}
}
$a = new A();
$b = new B();
$c = new C();
echo isset($a->test) ? $a->test : 'nothing'; // "nothing"
echo $a->test ?? 'nothing'; // "a value", isset() is not called!
echo isset($b->test) ? $b->test : 'nothing'; // "nothing"
echo $b->test ?? 'nothing'; // "nothing", __isset() is called
echo isset($c->test) ? $c->test : 'nothing'; // throw an Exception
echo $c->test ?? 'nothing'; // "nothing"
?>
azz ¶
4 years ago
Keep in mind that ?: operator is NOT fully equal to empty()
?: can't check non-existent array index (as describe here https://www.php.net/manual/ru/language.operators.comparison.php#92685) and vars
Check this:
<?php
ini_set('error_reporting', E_ALL);
$t = [];
var_dump(!isset($t['z']) || $t['z'] == FALSE); // true, this that empty() do
var_dump(empty($t['z'])); // true
var_dump(isset($t['z'])); // false
$v1 = $t['z'] ?: false; // Notice: Undefined index: z
$v2 = $t['z'] ?? false; // silent!
var_dump($v1); // false
var_dump($v2); // false
var_dump(!isset($non_existent_var) || $non_existent_var == FALSE); // true, this that empty() do
var_dump(empty($non_existent_var)); // true
var_dump(isset($non_existent_var)); // false
$v1 = $non_existent_var ?: false; // Notice: Undefined variable: non_existent_var
$v2 = $non_existent_var ?? false; // silent!
var_dump($v1); // false
var_dump($v2); // false
j-a-n at gmx dot de ¶
12 years ago
Please be careful when comparing strings with floats, especally when you are using the , as decimal.
<?php
var_dump($alt);
var_dump($neu);
var_dump($alt == $neu);
?>
string(9) "590217,73"
float(590217,73)
bool(false)
not the float is cast to a string and then string-compared, but the string is cast to a float and then float-compared.
to compare as strings use strval!
<?php
var_dump(strval($alt));
var_dump(strval($neu));
var_dump(strval($alt) == strval($neu));
?>
string(9) "590217,73"
string(9) "590217,73"
bool(true)
user@example ¶
19 years ago
With Nested ternary Operators you have to set the logical parentheses to get the correct result.
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : ($test2) ? "TEST2 true" : "false";
?>
This will output: TEST2 true;
correct:
<?php
$test=true;
$test2=true;
($test) ? "TEST1 true" : (($test2) ? "TEST2 true" : "false");
?>
Anyway don't nest them to much....!!
Ryan Mott ¶
4 years ago
Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)
sgurukrupa at gmail dot com ¶
9 years ago
With respect to using the ternary operator as a 'null-coalescing' operator: expr1 ?: expr2, note that expr1 is evaluated only once.
zak at minion dot net ¶
12 years ago
be careful when trying to concatenate the result of a ternary operator to a string
<?php
print '<div>'.(FALSE) ? 'TRUE [bad ternary]' : 'FALSE [bad ternary]';
print '<br><br>';
print '<div>'.((FALSE) ? 'TRUE [good ternary]' : 'FALSE [good ternary]');
?>
yields:
TRUE [bad ternary]
FALSE [good ternary]
this is because the ternary evaluates '<div>'.(FALSE) not (FALSE) - so the end result is TRUE
taras dot bogach at gmail dot com ¶
13 years ago
Boolean switch usege
<?php
class User_Exception extends Exception{}
class User{
public function register($login,$pass,$passCheck)
switch(false){
case(strlen($pass) >= 5):
throw new User_Exception("Password must be at last 5 chars length");
case($pass == $passCheck):
throw new User_Exception("Password is not confirmed!");
case(strlen($login) >= 5):
throw new User_Exception("Login must be at last 5 chars length");
//Do other checks
default:
//Do registration
return true;
}
}
//...
}
?>
damien dot launay dot mail at gmail dot com ¶
10 years ago
I found a nice way to use of new "?:" operator:
$a = array();
$a['foo'] = 'oof';
$b = @ ($a['foo'] ?: 'No foo');
$c = @ ($a['bar'] ?: 'No bar');
var_dump($b, $c);
Output:
string(3) "oof"
string(6) "No bar"
No error is thrown and $c is set with correct value.
Benefit: no need to use isset.
halfhearted13 at gmail dot com ¶
3 years ago
Both Null Coalescing ( ?? ) and Ternary ( ? : ) can work at a time.
<?php
$a = "user name";
echo $a = null ?? $a ? "sb" : "not found"; // it prints : sb
//as null coalescing has null on left it goes to 2nd expr $a. $a is defined so //output will be the 1st expr of Ternay operator.
?>
<?php
echo $x = "" ?? "" ? : "not found"; // it prints: not found.
// null coalescing has empty value of its left. so it prints right expr which is //also empty. so the output will be the 2nd expr of ternary(written in short)
?>
<?php
echo $x = "" ?? "" ?? "" ? : false; // prints nothing.
// if you add var_dump() you see bool(false)
?>
yiminrong at yahoo dot ca ¶
2 years ago
The string equality operator has a big gotcha in that if both operators match the format /^0+[Ee][0-9]+$/, then the values will be considered equal. All these, which represent common use cases, will output true:
echo '0e56' == '0E31'; // comparing short hex strings
echo md5('240610708') == md5('QNKCDZO'); // comparing hashes - see comment by Ray Paseur in md5 function
echo '000e123' == '00e0123'; // permutation of a string
The reason is that strings in the format /^0+[Ee][0-9]+$/ are interpreted as a number in scientific notation and zero raised to any power is zero.
Unless it is certain that the string will not match the specific format, then === should be used instead of == for strings.
Tahazzot ¶
2 years ago
Very careful when reading PHP documentation, Here's a lot of miss information.
According to documentation, They say's (int) 0 == (string) "a" is true. But it is not in PHP 8.
var_dump(0 == "a"); // 0 == 0 -> true
Now In PHP 8 it's False.
Ireneusz Pachulski ¶
3 years ago
Note that spaceship operator (<=>) is binary safe.
<?php
$a = "Hello";
$b = "Hello\x00World";
echo ($a <=> $b) . "<br>"; // -1
echo strcmp($a, $b) . "<br>"; // -6
echo strcoll($a, $b) . "<br>"; // 0 => not binary safe
?>
instatiendaweb at gmail dot com ¶
2 years ago
switch ("a") {
case 0:
echo "0";
break;
case "a": // nunca alcanzado debido a que "a" ya ha coincidido con 0
echo "a";
break;
}
In php 8.0 is echo "a";
mail at markuszeller dot com ¶
13 years ago
I prefer writing (!$a == 'hello') much more than ($a != 'hello'), but I wondered about the performance.
So I did a benchmark:
<?php
for($bench = 0; $bench < 3; $bench++)
{
$start = microtime(true);
$a = 1;
for($i = 0; $i < 100000000; $i++)
{
if(!$a == 'hello') $b++;
}
$end = microtime(true);
echo "Used time: " . ($end-$start) . "\n";
}
?>
and it results with
# if($a != 'hello')
Used time: 12.552895069122
Used time: 12.548940896988
Used time: 12.470285177231
# if(!$a == 'hello')
Used time: 7.6532161235809
Used time: 7.6426539421082
Used time: 7.6452689170837
