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Comparison Operators

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

Example

Name

Result

$a == $b

Equal

TRUE if $a is equal to $b after type juggling.

$a === $b

Identical

TRUE if $a is equal to $b, and they are of the same type.

$a != $b

Not equal

TRUE if $a is not equal to $b after type juggling.

$a <> $b

Not equal

TRUE if $a is not equal to $b after type juggling.

$a !== $b

Not identical

TRUE if $a is not equal to $b, or they are not of the same type.

$a < $b

Less than

TRUE if $a is strictly less than $b.

$a > $b

Greater than

TRUE if $a is strictly greater than $b.

$a <= $b

Less than or equal to

TRUE if $a is less than or equal to $b.

$a >= $b

Greater than or equal to

TRUE if $a is greater than or equal to $b.

$a <=> $b

Spaceship

An integer less than, equal to, or greater than zero when $a is respectively less than, equal to, or greater than $b. Available as of PHP 7.

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.

代码语言：javascript
复制
<?php
var_dump(0?==?"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":?//?never?reached?because?"a"?is?already?matched?with?0
????echo?"a";
????break;
}
?>
代码语言：javascript
复制
<?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
?
//?only?values?are?compared
$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

null or string

string

Convert NULL to "", numerical or lexical comparison

bool or null

anything

Convert both sides to bool, FALSE < TRUE

object

object

Built-in classes can define its own comparison, different classes are uncomparable, same class - compare properties the same way as arrays (PHP 4), PHP 5 has its own explanation

string, resource or number

string, resource or number

Translate strings and resources to numbers, usual math

array

array

Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value (see following example)

object

anything

object is always greater

array

anything

array is always greater

Example #1 Boolean/null comparison

代码语言：javascript
复制
<?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
?>

Example #2 Transcription of standard array comparison

代码语言：javascript
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<?php
//?Arrays?are?compared?like?this?with?standard?comparison?operators
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
}
?>

See also strcasecmp(), strcmp(), Array operators, and the manual section on Types.

Warning

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

See the documentation for float for more information.

Ternary Operator

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

Example #3 Assigning a default value

代码语言：javascript
复制
<?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'];
}

?>

The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE.

Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.

Note: 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 return $var == 42 ? $a : $b; in a return-by-reference function will therefore not work and a warning is issued.

Note: It is recommended that you avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious: Example #4 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' //?this?is?because?ternary?expressions?are?evaluated?from?left?to?right //?the?following?is?a?more?obvious?version?of?the?same?code?as?above echo?((true???'true'?:?false)???'t'?:?'f'); //?here,?you?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. ?>

Null Coalescing Operator

Further exists the "??" (or null coalescing) operator, available as of PHP 7.

Example #5 Assigning a default value

代码语言：javascript
复制
<?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';
}

?>

The expression (expr1) ?? (expr2) evaluates to expr2 if expr1 is NULL, and expr1 otherwise.

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

Note: 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 return $foo ?? $bar; in a return-by-reference function will therefore not work and a warning is issued.

Note: Please note that the null coalescing operator allows for simple nesting: Example #6 Nesting null coalescing operator <?php $foo?=?null; $bar?=?null; $baz?=?1; $qux?=?2; echo?$foo????$bar????$baz????$qux;?//?outputs?1 ?>

← Bitwise Operators

Error Control Operators →

代码语言：txt
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 ? 1997–2017 The PHP Documentation Group

Licensed under the Creative Commons Attribution License v3.0 or later.

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