Comparison Operators

Comparison Operators

Comparison operators, as their name implies, allow you to compare two values. You may also be interested in viewing , as they show examples of various type related comparisons. the type comparison tables

| Example | Name | Result | | --- | --- | --- | | $a == $b | Equal | true if is equal to after type juggling. | | $a === $b | Identical | true if is equal to , and they are of the same type. | | $a != $b | Not equal | true if is not equal to after type juggling. | | $a $b | Not equal | true if is not equal to after type juggling. | | $a !== $b | Not identical | true if is not equal to , or they are not of the same type. | | $a < $b | Less than | true if is strictly less than . | | $a > $b | Greater than | true if is strictly greater than . | | $a | Less than or equal to | true if is less than or equal to . | | $a >= $b | Greater than or equal to | true if is greater than or equal to . | | $a $b | Spaceship | An less than, equal to, or greater than zero when is less than, equal to, or greater than , respectively. |

If both operands are , or one operand is a number and the other one is a , then the comparison is done numerically. These rules also apply to the statement. The type conversion does not take place when the comparison is or as this involves comparing the type as well as the value. numeric stringsnumeric stringswitch===``!==

Waarschuwing: > Prior to PHP 8.0.0, if a is compared to a number or a numeric string then the was converted to a number before performing the comparison. This can lead to surprising results as can be seen with the following example:

`string``string````php

```php
bool(true)
bool(true)
bool(true)
bool(true)
0

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

Voorbeeld: Comparison Operators

<?php
// Integers
echo 1 <=> 1, ' '; // 0
echo 1 <=> 2, ' '; // -1
echo 2 <=> 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 [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

// 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

// not only values are compared; keys must match
$a = (object) ["a" => "b"];
$b = (object) ["b" => "b"];
echo $a <=> $b, ' '; // 1

?>

For various types, comparison is done according to the following table (in order).

| Type of Operand 1 | Type of Operand 2 | Result | | --- | --- | --- | | or | | Convert null to "", numerical or lexical comparison | | or | anything | Convert both sides to , false < true | | | | Built-in classes can define its own comparison, different classes are incomparable, same class see | | , , or | , , or | Translate strings and resources to numbers, usual math | | | | Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are incomparable, otherwise - compare value by value (see following example) | | | anything | is always greater | | | anything | is always greater |

Voorbeeld: Boolean/null comparison

<?php
// Bool and null are compared as bool always
var_dump(1 == TRUE);  // TRUE - same as (bool) 1 == TRUE
var_dump(0 == 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, -10, NULL, 10, 100)); // NULL - (bool) NULL < (bool) -100 is FALSE < TRUE
?>

Voorbeeld: Transcription of standard array comparison

<?php
// Arrays are compared like this with standard comparison operators as well as the spaceship operator.
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
}
?>

Waarschuwing: > ### Comparison of floating point numbers

Because of the way s are represented internally, you should not test two s for equality. float``float

See the documentation for for more information. float

Opmerking: > Be aware that PHP's type juggling is not always obvious when comparing values of different types, particularly comparing integers to booleans or integers to strings. It is therefore generally advisable to use and comparisons rather than and in most cases. ===``!==``==``!=

Incomparable Values

While identity comparison ( and ) can be applied to arbitrary values, the other comparison operators should only be applied to comparable values. The result of comparing incomparable values is undefined, and should not be relied upon. ===``!==

strcasecmp``strcmpArray operatorsTypes

Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.

The expression evaluates to if evaluates to true, and if evaluates to false. Voorbeeld: Assigning a default value

<?php
// Example usage for: Ternary Operator
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// The above is identical to this if/else statement
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}
?>

(expr1) ? (expr2) : (expr3)

It is possible to leave out the middle part of the ternary operator. Expression evaluates to the result of if evaluates to true, and otherwise. is only evaluated once in this case. expr1 ?: expr3

Opmerking: > Please note that the ternary operator is an expression, and that it doesn't evaluate to a variable, but to the result of an expression. This is important to know if you want to return a variable by reference. The statement in a return-by-reference function will therefore not work and a warning is issued. return $var == 42 ? $a : $b;

Opmerking: > It is recommended to avoid "stacking" ternary expressions. PHP's behaviour when using more than one unparenthesized ternary operator within a single expression is non-obvious compared to other languages. Indeed prior to PHP 8.0.0, ternary expressions were evaluated left-associative, instead of right-associative like most other programming languages. Relying on left-associativity is deprecated as of PHP 7.4.0. As of PHP 8.0.0, the ternary operator is non-associative.

Voorbeeld: Non-obvious Ternary Behaviour

<?php
// on first glance, the following appears to output 'true'
echo (true ? 'true' : false ? 't' : 'f');

// however, the actual output of the above is 't' prior to PHP 8.0.0
// this is because ternary expressions are left-associative

// the following is a more obvious version of the same code as above
echo ((true ? 'true' : false) ? 't' : 'f');

// here, one can see that the first expression is evaluated to 'true', which
// in turn evaluates to (bool) true, thus returning the true branch of the
// second ternary expression.
?>

Opmerking: > Chaining of short-ternaries (), however, is stable and behaves reasonably. It will evaluate to the first argument that evaluates to a non-falsy value. Note that undefined values will still raise a warning.

?:Voorbeeld: Short-ternary chaining

<?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 Coalescing Operator

Another useful shorthand operator is the "??" (or null coalescing) operator.

The expression evaluates to if is null, and otherwise. Voorbeeld: Assigning a default value

<?php
// Example usage for: Null Coalesce Operator
$action = $_POST['action'] ?? 'default';

// The above is identical to this if/else statement
if (isset($_POST['action'])) {
    $action = $_POST['action'];
} else {
    $action = 'default';
}
?>

(expr1) ?? (expr2)

In particular, this operator does not emit a notice or warning if the left-hand side value does not exist, just like . This is especially useful on array keys. isset

Opmerking: > Please note that the null coalescing operator is an expression, and that it doesn't evaluate to a variable, but to the result of an expression. This is important to know if you want to return a variable by reference. The statement in a return-by-reference function will therefore not work and a warning is issued. return $foo ?? $bar;

Opmerking: > The null coalescing operator has low precedence. That means if mixing it with other operators (such as string concatenation or arithmetic operators) parentheses will likely be required.

<?php
// Raises a warning that $name is undefined.
print 'Mr. ' . $name ?? 'Anonymous';

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

Opmerking: > Please note that the null coalescing operator allows for simple nesting:

Voorbeeld: Nesting null coalescing operator

<?php

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

echo $foo ?? $bar ?? $baz ?? $qux; // outputs 1

?>