Operatori di confronto

Gli operatori di confronto, come suggerisce il loro nome, permettono di confrontare due valori. Può essere interessante vedere la tabella di raffronto dei tipi, dato che mostra esempi di vari confronti tra i tipi di variabili.

Operatori di confronto
Esempio Nome Risultato
$a == $b Uguale true se $a è uguale a $b dopo la manipolazione dei tipi.
$a === $b Identico true se $a è uguale a $b, ed sono dello stesso tipo.
$a != $b Diversi true se $a è diverso da $b dopo la manipolazione dei tipi.
$a <> $b Diversi true se $a è diverso da $b dopo la manipolazione dei tipi.
$a !== $b Non identici true se $a è diverso da $b, o se non sono dello stesso tipo.
$a < $b Minore true se $a è strettamente minore di $b.
$a > $b Maggiore true se $a è strettamente maggiore di $b.
$a <= $b Minore o uguale true se $a è minore o uguale a $b.
$a >= $b Maggiore o uguale true se $a è maggiore o uguale a $b.
$a <=> $b Spaceship Un int minore di, uguale a, o maggiore di zero quando $a è minore di, uguale a, o maggiore di $b.

Se entrambi gli operandi sono stringhe numeriche o un operando è un numero e l'altro è una stringa numerica, quindi il confronto viene eseguito numericamente. Queste regole si applicano anche all' istruzione switch. La conversione del tipo non ha luogo quando il confronto è === o !== poiché implica il confronto del tipo e del valore.

Avviso

Prima di PHP 8.0.0, se una stringa veniva confrontata con un numero o una stringa numerica, la stringa veniva convertita in un numero prima di eseguire il confronto. Questo può portare a risultati sorprendenti, come si può vedere con il seguente esempio:

<?php
var_dump
(== "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;
}
?>

Output of the above example in PHP 7:

bool(true)
bool(true)
bool(true)
bool(true)
0

Output of the above example in PHP 8:

bool(false)
bool(true)
bool(true)
bool(true)
a

<?php  
// Interi
echo <=> 1// 0
echo <=> 2// -1
echo <=> 1// 1
 
// Numeri float
echo 1.5 <=> 1.5// 0
echo 1.5 <=> 2.5// -1
echo 2.5 <=> 1.5// 1
 
// Stringhe
echo "a" <=> "a"// 0
echo "a" <=> "b"// -1
echo "b" <=> "a"// 1
 
echo "a" <=> "aa"// -1
echo "zz" <=> "aa"// 1
 
// Array
echo [] <=> []; // 0
echo [123] <=> [123]; // 0
echo [123] <=> []; // 1
echo [123] <=> [121]; // 1
echo [123] <=> [124]; // -1
 
// Oggetti
$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
 
// non vengono confrontati solo i valori; le chiavi devono corrispondere
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo 
$a <=> $b// 1

?>

Se i tipi di operandi utilizzati differiscono, il confronto viene svolto nell'ordine indicato della seguente tabella.

Confronti con differenti tipi
Tipo dell'operando 1 Tipo dell'operando 2 Risultato
null oppure string string Si converte null in "", confronto numerico o lessicale
bool oppure null qualsiasi Converte entrambi i lati in bool, false < true
object object Le classi predefinite possono avere la propria funzione di confronto, classi differenti non sono confrontabili, per la stessa classe vedere Confronto di Oggetti.
string, resource, int oppure float string, resource, int oppure float Stringhe e risorse sono converti in numeri, confronto matematico
array array La matrice con meno membri è più piccola, se la chiave dell'operando 1 non si trova nell'operando 2 allora le matrici non si possono confrontare, in altri casi il confronto avviene valore per valore (vedere l'esempio seguente)
object qualsiasi object è sempre più grande
array qualsiasi array è sempre più grande

Example #1 Confronto Boolean/null

<?php
// Bool e null sono confrontati sempre come bool
var_dump(== TRUE);  // TRUE - uguale a (bool)1 == TRUE
var_dump(== FALSE); // TRUE - uguale a (bool)0 == FALSE
var_dump(100 TRUE); // FALSE - uguale a (bool)100 < TRUE
var_dump(-10 FALSE);// FALSE - uguale a (bool)-10 < FALSE
var_dump(min(-100, -10NULL10100)); // NULL - (bool)NULL < (bool)-100 è FALSE < TRUE
?>

Example #2 Trascrizione del confronto standard tra matrici

<?php
// Gli array vengono confrontati in questo modo con gli operatori di confronto standard e con l'operatore spaceship.
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
}
?>

Avviso

Confronto di numeri in virgola mobile

A causa del modo in cui i float sono rappresentati internamente al PHP, non si dovrebbe esaminare l'eguaglianza di due float.

Per maggior informazioni, fare riferimento alla documentazione del tipo float.

Nota: Tenere presente che la manipolazione dei tipi di PHP non è sempre ovvia quando si confrontano valori di tipi diversi, in particolare confrontando int con bool o int con string. È quindi generalmente consigliabile utilizzare confronti === e !== piuttosto che == e != nella maggior parte dei casi.

Incomparable Values

Mentre il confronto di identità (=== e !==) può essere applicato a valori arbitrari, gli altri operatori di confronto dovrebbero essere applicati solo a valori comparabili. Il risultato del confronto di valori incomparabili non è definito e non dovrebbe essere considerato attendibile.

Operatore ternario

Un altro operatore condizionale è l'operatore ternario "?:".

Example #3 Assegnazione di un valore di default

<?php
// Esempio di utilizzo dell'operatore ternario
$action = (empty($_POST['action'])) ? 'default' $_POST['action'];

// La riga precedente è simile a
if (empty($_POST['action'])) {
    
$action 'default';
} else {
    
$action $_POST['action'];
}
?>
L'espressione (espressione1) ? (espressione2) : (espressione3) vale espressione2 se espressione1 è true, e espressione3 se espressione1 è false.

È possibile tralasciare l'elemento centrale dell'operatore ternario. L'espressione espressione1 ?: espressione3 viene valutata al risultato di espressione1 se espressione1 viene valutata true, e espressione3 in caso contrario. espressione1 viene valutata solo una volta.

Nota: Si noti che l'operatore ternario è un'espressione, e non viene valutato come variabile, ma come risultato di un'espressione. Questo è importante da sapere nel caso si desideri restituire una variabile per riferimento. La riga return $var == 42 ? $a : $b; in una funzione che restituisce per riferimento non funzionerà e genererà un avvertimento.

Nota:

Si raccomanda di evitare di "sovrapporre" espressioni ternarie. Il comportamento di PHP quando si utilizza più di un operatore ternario senza parentesi all'interno di una singola espressione non è ovvio rispetto ad altri linguaggi. In effetti, prima di PHP 8.0.0, le espressioni ternarie venivano valutate associative a sinistra, anziché associative a destra come la maggior parte degli altri linguaggi di programmazione. Fare affidamento sull'associatività di sinistra è deprecato a partire da PHP 7.4.0. A partire da PHP 8.0.0, l'operatore ternario non è associativo.

Example #4 Comportamento ternario non ovvio

<?php
// a prima vista, questa istruzione dovrebbe restituire 'true'
echo (true 'true' false 't' 'f');

// invece, l'output effettivo di quanto sopra è 't' prima di PHP 8.0.0
// questo perché le espressioni ternarie sono associative a sinistra

// quanti segue è una versione più chiara dello stesso codice
echo ((true 'true' false) ? 't' 'f');

// qui, si può notare che la prima espressione viene valutata come "true", che
// a sua volta diventa (bool)true, e quindi restituisce il ramo true della
// seconda espressione ternaria.
?>

Nota:

Il concatenamento di ternari brevi (?:), tuttavia, è stabile e si comporta in modo ragionevole. Verrà valutato al primo argomento valutato come valore non falso. Si noti che i valori non definiti genereranno comunque un avviso.

Example #5 Concatenamento ternario breve

<?php
echo ?: ?: ?: 3PHP_EOL//1
echo ?: ?: ?: 3PHP_EOL//2
echo ?: ?: ?: 3PHP_EOL//3
?>

L'operatore Null Coalescing

Un altro utile operatore abbreviato è il "??" (o null coalescing).

Example #6 Assegnazione di un valore predefinito

<?php
// Esempio di utilizzo per: Operatore Null Coalesce
$action $_POST['action'] ?? 'default';

// Quello sopra è identico a questa istruzione if/else
if (isset($_POST['action'])) {
    
$action $_POST['action'];
} else {
    
$action 'default';
}
?>
L'espressione (expr1) ?? (expr2) viene valutata a expr2 se expr1 è null, e expr1 in caso contrario.

In particolare, questo operatore non emette un avviso o un avvertimento se il valore del lato sinistro non esiste, proprio come isset(). Questo è particolarmente utile sulle chiavi degli array.

Nota: Si prega di notare che l'operatore null coalescing è un'espressione, e che essa non viene valutata ad una variabile, ma al risultato di un'espressione. Questo è importante da sapere nel caso in cui si volesse restituire una variabile per riferimento. L'istruzione return $foo ?? $bar; in una funzione che restituisce un riferimento quindi non funzionerà e verrà emesso un avviso.

Nota:

L'operatore null coalescing ha una precedenza bassa. Ciò significa che se lo si mescola con altri operatori (come la concatenazione di stringhe o gli operatori aritmetici) saranno probabilmente necessarie parentesi.

<?php
// Genera un avviso che $name non è definito.
print 'Mr. ' $name ?? 'Anonymous';

// Stampa "Mr. Anonymous"
print 'Mr. ' . ($name ?? 'Anonymous');
?>

Nota:

Si prega di notare che l'operatore null coalescing permette semplici nidificazioni:

Example #7 Operatore null coalescing nidificato

<?php

$foo 
null;
$bar null;
$baz 1;
$qux 2;

echo 
$foo ?? $bar ?? $baz ?? $qux// stampa 1

?>

add a note add a note

User Contributed Notes 45 notes

up
144
crazy888s at hotmail dot com
12 years ago
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.
up
88
arnaud at arnapou dot net
12 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 !
up
46
Harry Willis
8 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...)
up
31
thomas dot oldbury at tgohome dot com
15 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.
up
36
jwhiting at hampshire dot edu
18 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...
up
20
jeronimo at DELETE_THIS dot transartmedia dot com
18 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

?>
up
34
mail at mkharitonov dot net
8 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
up
20
hiroh2k at yahoo dot com
18 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.
up
39
Anonymous
17 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
up
17
kapoor_rajiv at hotmail dot com
13 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>';

?>
up
20
rshawiii at yahoo dot com
16 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
}
?>
up
15
Jeremy Swinborne
10 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
up
8
G
5 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
?>
up
18
gondo
8 years ago
beware of the fact, that there is no `<==` nor `>==` therefore `false <= 0` will be `true`. php v. 5.4.27
up
16
Alex
16 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).
up
5
niall at maranelda dot org
5 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.
?>
up
19
adam at caucho dot com
16 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...
up
13
bishop
16 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)
up
13
Cuong Huy To
11 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)
up
17
stepheneliotdewey at gmail [period] com
15 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 !==).
up
1
itsacon at itsacon dot net
1 year 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
up
4
prezire at gmail dot com
6 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
?>
up
1
Sumon Mahmud
2 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
up
13
Anonymous
13 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.
up
11
bimal at sanjaal dot com
9 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.
up
9
alan dot g at nospam dot net
12 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;
}



?>
up
10
Hayley Watson
15 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.
up
13
fernandoleal at dragoncs dot com
15 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;
?>
up
7
Mark Simon
11 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;
up
4
Marcin Kuzawiski
7 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
up
3
Romain
4 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"

?>
up
2
azz
3 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
up
6
j-a-n at gmx dot de
11 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)
up
8
user@example
18 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....!!
up
2
Ryan Mott
3 years ago
Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)
up
2
sgurukrupa at gmail dot com
8 years ago
With respect to using the ternary operator as a 'null-coalescing' operator: expr1 ?: expr2, note that expr1 is evaluated only once.
up
5
zak at minion dot net
11 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
up
4
taras dot bogach at gmail dot com
12 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;
    }
  }
 
//...
}
?>
up
1
damien dot launay dot mail at gmail dot com
9 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.
up
1
halfhearted13 at gmail dot com
2 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 $x = "" ?? "" ?? "" ? : false// prints nothing.
// if you add var_dump() you see bool(false)
?>
up
0
yiminrong at yahoo dot ca
1 year ago
The string equality operator has a big gotcha in that if both operators match the format /^0+[Ee][0-9]+$/, 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.
up
-1
Tahazzot
1 year 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.
up
-1
Ireneusz Pachulski
2 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, $b) . "<br>"; // 0 => not binary safe
?>
up
-2
instatiendaweb at gmail dot com
1 year ago
switch ("a") {
case 0:
    echo "0";
    break;
case "a": // nunca alcanzado debido a que "a" ya ha coincidido con 0
    echo "a";
    break;
}
In php 8.0 is echo "a";
up
-1
mail at markuszeller dot com
12 years ago
I prefer writing (!$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
To Top