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.
Comparison Operators$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 | Greater than or equal to | true if $a is greater than or equal to $b.
|
$a $b | Spaceship | An int less than, equal to, or greater than zero when $a is less than, equal to, or greater than $b, respectively. |
If both operands are numeric strings, or one operand is a number and the other one is a numeric string, then the comparison is done 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.
Warning
Prior to PHP 8.0.0, if a string is compared to a number or a numeric string then the string was converted to a number before performing the comparison. This can lead to surprising results as can be seen with the following example:
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
For various types, comparison is done according to the following table [in order].
Comparison with Various Typesnull 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 incomparable, same class see Object Comparison |
string, resource, int or float | string, resource, int or float | 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 incomparable, 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
Example #2 Transcription of standard array comparison
Warning
Comparison of floating point numbers
Because of the way floats are represented internally, you should not test two floats for equality.
See the documentation for float for more information.
Note: Be aware that PHP's type juggling is not always obvious when comparing values of different types, particularly comparing ints to bools or ints 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.
Ternary Operator
Another conditional operator is the "?:" [or ternary] operator.
Example #3 Assigning a default value
The expression [expr1] ? [expr2] : [expr3]
evaluates to expr2 if expr1 evaluates to true
, and expr3 if expr1 evaluates to false
.
It is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3
evaluates to the result of expr1 if expr1 evaluates to
true
, and expr3 otherwise. expr1 is only evaluated once in this case.
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 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.
Example #4 Non-obvious Ternary Behaviour
Note:
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.Example #5 Short-ternary chaining
Null Coalescing Operator
Another useful shorthand operator is the "??" [or null coalescing] operator.
Example #6 Assigning a default value
The expression [expr1] ?? [expr2]
evaluates to expr2 if expr1 is null
, and expr1 otherwise.
In particular, this operator does not emit a notice or warning 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:
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.
Note:
Please note that the null coalescing operator allows for simple nesting:
Example #7 Nesting null coalescing operator
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:
It works just as expected, returning the first non-false value within a group of expressions.
niall at maranelda dot org ¶
4 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:
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:
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...
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.
bishop ¶
15 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:
To answer that question, use:
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:
Example:
[See also the solution "rshawiii at yahoo dot com" posted]
Sumon Mahmud ¶
2 years ago
Extending from here: //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 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
admin at zeros dot co dot id ¶
1 month ago
Please be careful when you try to compare strings that have a plus sign `+` at the beginning [such as phone number, etc]. When you use the Equal operator `==` PHP will ignore the plus sign. Use Identical operator `===` instead
Example:
$str1 = "62";
$str2 = "+62";
var_dump[$str1 == $str2]; // bool[true]
var_dump[$str1 === $str2]; // bool[false]
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.