Midwest PHP Call For Papers Open

Operadores de comparación

Los operadores de comparación, como su nombre lo indica, permiten comparar dos valores. Puede también estar interesado en ver las tablas de comparación de tipos, ya que muestran ejemplos de las varias comparaciones relacionadas con tipos.

Operadores de comparación
Ejemplo Nombre Resultado
$a == $b Igual TRUE si $a es igual a $b después de la manipulación de tipos.
$a === $b Idéntico TRUE si $a es igual a $b, y son del mismo tipo.
$a != $b Diferente TRUE si $a no es igual a $b después de la manipulación de tipos.
$a <> $b Diferente TRUE si $a no es igual a $b después de la manipulación de tipos.
$a !== $b No idéntico TRUE si $a no es igual a $b, o si no son del mismo tipo.
$a < $b Menor que TRUE si $a es estrictamente menor que $b.
$a > $b Mayor que TRUE si $a es estrictamente mayor que $b.
$a <= $b Menor o igual que TRUE si $a es menor o igual que $b.
$a >= $b Mayor o igual que TRUE si $a es mayor o igual que $b.
$a <=> $b Nave espacial Un integer menor que, igual a, o mayor que cero cuando $a es respectivamente menor que, igual a, o mayor que $b. Disponible a partir de PHP 7.
$a ?? $b ?? $c Fusión de null El primer operando de izquierda a derecha que exista y no sea NULL. NULL si no hay valores definidos y no son NULL. Disponible a partir de PHP 7.

Si se compara un número con un string o la comparación implica strings numéricos, entonces cada string es convertido en un número y la comparación realizada numéricamente. Estas reglas también se aplican a la sentencia switch. La conversión de tipo no tiene lugar cuando la comparación es === o !== ya que esto involucra comparar el tipo así como el valor.

<?php
var_dump
(== "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

switch ("a") {
case 
0:
    echo 
"0";
    break;
case 
"a"// nunca alcanzado debido a que "a" ya ha coincidido con 0
    
echo "a";
    break;
}
?>
<?php  
// Integers
echo <=> 1// 0
echo <=> 2// -1
echo <=> 1// 1
 
// Floats
echo 1.5 <=> 1.5// 0
echo 1.5 <=> 2.5// -1
echo 2.5 <=> 1.5// 1
 
// Strings
echo "a" <=> "a"// 0
echo "a" <=> "b"// -1
echo "b" <=> "a"// 1
 
echo "a" <=> "aa"// -1
echo "zz" <=> "aa"// 1
 
// Arrays
echo [] <=> []; // 0
echo [123] <=> [123]; // 0
echo [123] <=> []; // 1
echo [123] <=> [121]; // 1
echo [123] <=> [124]; // -1
 
// Objects
$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
 
// only values are compared
$a = (object) ["a" => "b"]; 
$b = (object) ["b" => "b"]; 
echo 
$a <=> $b// 1

?>

Para varios tipos, la comparación se realiza de acuerdo a la siguiente tabla (en orden).

La comparación con varios tipos
Tipo de operando 1 Tipo de operando 2 Resultado
null o string string Convierte NULL en "", comparación numérica o léxica
bool o null cualquiera Convierte ambos lados a bool, FALSE < TRUE
object object Las clases internas pueden definir su propia comparación, diferentes clases son incomparables, la misma clase - comparan propiedades en la misma forma que los arrays (PHP 4), PHP 5 tiene su propia explicación
string, resource o number string, resource o number Traducir las cadenas y recursos a números, matemática usual
array array Un array con menos elementos es menor, si una clave del operando 1 no se encuentra en el operando 2 entonces los arrays son incomparables, de otra forma - compara valor por valor (ver el siguiente ejemplo)
object cualquiera object es siempre mayor
array cualquiera array es siempre mayor

Ejemplo #1 Comparación boolean/null

<?php
// Booleanos y null son comparados siempre coomo bool
var_dump(== TRUE);  // TRUE - same as (bool)1 == TRUE
var_dump(== FALSE); // TRUE - same as (bool)0 == FALSE
var_dump(100 TRUE); // FALSE - same as (bool)100 < TRUE
var_dump(-10 FALSE);// FALSE - same as (bool)-10 < FALSE
var_dump(min(-100, -10NULL10100)); // NULL - (bool)NULL < (bool)-100 is FALSE < TRUE
?>

Ejemplo #2 Transcripción de la comparación estándar de arrays

<?php
// Arrays son comparados de esta forma con los operadores de comparación estándar
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 
null// uncomparable
        
} elseif ($val $op2[$key]) {
            return -
1;
        } elseif (
$val $op2[$key]) {
            return 
1;
        }
    }
    return 
0// $op1 == $op2
}
?>

Ver también strcasecmp(), strcmp(), operadores de array, y la sección del manual sobre tipos.

Advertencia

Comparación de números de punto flotante

Debido a la forma en que son representados internamente los floats, no se deben probar por igualdad dos floats.

Ver la documentación de float para más información.

Operador ternario

Otro operador condicional es el operador "?:" (o ternario).

Ejemplo #3 Asignación de un valor predeterminado

<?php
// Ejemplo de uso para: Operador Ternario
$action = (empty($_POST['action'])) ? 'default' $_POST['action'];

// Lo anterior es idéntico a esta sentencia if/else
if (empty($_POST['action'])) {
    
$action 'default';
} else {
    
$action $_POST['action'];
}

?>
La expresión (expr1) ? (expr2) : (expr3) evalúa a expr2 si expr1 se evalúa como TRUE y a expr3 si expr1 se evalúa como FALSE.

A partir de PHP 5.3, es posible dejar de lado la parte media del operador ternario. La expresión expr1 ?: expr3 retorna expr1 si expr1 se evalúa como TRUE y expr3 si es de otra manera.

Nota: Por favor note que el operador ternario es una expresión, y que no evalúa a una variable, sino al resultado de una expresión. Esto es importante saberlo si se desea retornar una variable por referencia. La sentencia return $var == 42 ? $a : $b; en una función con retorno-por-referencia no funcionará por lo que se ha mencionado y una advertencia es generada en versiones posteriores de PHP.

Nota:

Es recomendable evitar el "apilamiento" expresiones ternarias. El comportamiento de PHP al utilizar más de un operador ternario en una única sentencia no es evidente:

Ejemplo #4 Comportamiento Ternario poco obvio

<?php
// a primera vista, lo siguiente parece tener la salida de 'true'
echo (true?'true':false?'t':'f');

// sin embargo, la salida real de lo anterior es 't'
// esto se debe a que las expresiones ternarias se evalúan de izquierda a derecha

// la siguiente es una versión más obvia del mismo código anterior
echo ((true 'true' false) ? 't' 'f');

// aquí, se puede ver que la primera expresión es evaluada como 'true', que
// a su vez se evalúa como (bool)true, retornando así la rama verdadera de la
// segunda expresión ternaria.
?>

add a note add a note

User Contributed Notes 44 notes

up
129
crazy888s at hotmail dot com
9 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
69
arnaud at arnapou dot net
9 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
42
Harry Willis
5 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
jwhiting at hampshire dot edu
15 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
32
mail at mkharitonov dot net
5 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
29
thomas dot oldbury at tgohome dot com
12 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
41
Anonymous
14 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
16
hiroh2k at yahoo dot com
15 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
14
bishop
13 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
19
stepheneliotdewey at gmail [period] com
12 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
12
jeronimo at DELETE_THIS dot transartmedia dot com
15 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
19
rshawiii at yahoo dot com
13 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
19
adam at caucho dot com
13 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
14
Cuong Huy To
8 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
11
Jeremy Swinborne
7 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
5
G
2 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
12
kapoor_rajiv at hotmail dot com
10 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
14
Anonymous
10 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.
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13
gondo
5 years ago
beware of the fact, that there is no `<==` nor `>==` therefore `false <= 0` will be `true`. php v. 5.4.27
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3
niall at maranelda dot org
1 year 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.
?>
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11
bimal at sanjaal dot com
6 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.
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12
Alex
13 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).
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9
alan dot g at nospam dot net
9 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;
}



?>
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10
Hayley Watson
12 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.
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11
user@example
15 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....!!
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13
fernandoleal at dragoncs dot com
12 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;
?>
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3
Marcin Kuzawiski
4 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
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3
sgurukrupa at gmail dot com
5 years ago
With respect to using the ternary operator as a 'null-coalescing' operator: expr1 ?: expr2, note that expr1 is evaluated only once.
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2
Romain
1 year 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"

?>
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5
Mark Simon
8 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;
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5
j-a-n at gmx dot de
8 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)
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1
Tero Lahtinen
3 months ago
?? this operator does not emit a notice if the left-hand side value does not exist, just like isset()

However, note that

$a = (float) $foo['bar'] ?? 1;

Does emit a warning, as the (float) $foo['bar'] is evaluated first, e.g. it is equivalent to

$a = ( (float) $foo['bar']) ?? 1;

Not to

$a (float) ( $foo['bar'] ?? 1);
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1
prezire at gmail dot com
3 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
?>
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5
zak at minion dot net
8 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
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3
damien dot launay dot mail at gmail dot com
6 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.
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1
phpnotes at zavaboy dot com
1 year ago
A note on null coalescing operators with arithmetic as it may not be obvious for some people.

<?php

// Only $a and $c are defined as:
$a = 4; $c = 2;

// When you do this:
echo  $a ?? 0 + $b ?? 0 + $c ?? 0 ; // 4

// You may have expected a result like this:
echo ($a ?? 0)+($b ?? 0)+($c ?? 0); // 6

// But this is basically what's going on:
echo  $a ??(0 + $b)??(0 + $c)?? 0 ; // 4

?>

Also note the first and last will produce an E_NOTICE if $a is not defined or null and $b is not defined:
Notice: Undefined variable: b in __FILE__ on line __LINE__

See also:
http://php.net/manual/en/language.operators.precedence.php
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4
taras dot bogach at gmail dot com
9 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;
    }
  }
 
//...
}
?>
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3
Boolean_Type
5 years ago
Nice and helpful article!)
I would like to ask:

number == null     - it converts both types of comparisons to a boolean or numeric type? In the table the author pointed out that to a boolean. But elsewhere I read that to a numeric type.
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2
toader_alexandru at yahoo dot com
7 years ago
it looks that

if you check 0 against a string with == then PHP returns true:

php -r 'var_dump(0 == "statuses");'
-> returns TRUE

but not if your string has a number at the beginning:

php -r 'var_dump(0 == "2statuses");'
-> returns FALSE

from the specs I get it that it attempts a conversion - in this case the string to number.

so better use ===
as always :)
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2
mail at markuszeller dot com
9 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
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1
email at kleijn dot jp
8 years ago
Maybe i am overlooking something but it seems to me that using unset(string) inside a ternary operator creates an error.

(($var1==0 && $var2==0)?unset($var3):$var3=$var1+$var2);

result:
Parse error: syntax error, unexpected T_UNSET

using the traditional form of IF...ELSE works normal.

if($var1==0 && $var2==0) { unset($var3); }
else { $var3=$var1+$var2; }

result:
This unsets var3 or creates a sum of var1+var2 for var3

JP Kleijn
Netherlands
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1
Amaroq
11 years ago
Most of the time, you may be content with your conditionals evaluating to true if they are evaluating a non-false, non-zero value. You may also like it when they evaluate to false when you use the number 0.

However, there may be times where you want to make a distinction between a non-false value and a boolean true. You may also wish to make a distinction between a boolean false and a zero.

The identity operator can make this distinction for you.

<?php
$a
= 'some string';
$b = 123;
$c = 0;

if(
$a && $b && (!$c))
{ echo
"True.\n"; } else { echo "False.\n"; }

if(
$a == true && $b == true && $c == false)
{ echo
"True.\n"; } else { echo "False.\n"; }

if(
$a === true || $b === true || $c === false)
{ echo
"True.\n"; } else { echo "False.\n"; }
?>

The above code outputs the following:
True.
True.
False.

As you can see, in the first two cases, $a and $b are considered true, while $c is considered false. If this wasn't the case, neither of the first two conditionals would have echoed "True."

In the last case, I've cleverly used the || operator to demonstrate that both $a and $b do not evaluate to true with the identity operator, nor does $c evaluate to false.

The === operator can be used to distinguish boolean from non-boolean values.
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0
azz
8 days 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
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0
Ryan Mott
1 month ago
Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)
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