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.

Comparison Operators
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.

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.

<?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"// never reached because "a" is already matched with 0
    
echo "a";
    break;
}
?>

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

Comparison with Various Types
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

<?php
// Bool and null are compared as bool always
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
?>

Example #2 Transcription of standard array comparison

<?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

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.

Ternary Operator

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

Example #3 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'];
}

?>
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 in later PHP versions.

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.
?>

Коментарии

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
}
?>
2006-01-18 13:36:34
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
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...
2006-05-09 01:49:59
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
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 (21);
$b = array (12);
// true === array_equal($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)
2006-10-26 18:49:53
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
I couldn't find much info on stacking the new ternary operator, so I ran some tests:

<?php
echo ?: ?: ?: 3//1
echo ?: ?: ?: 2//1
echo ?: ?: ?: 3//2
echo ?: ?: ?: 0//3

echo ?: ?: ?: 3//1
echo ?: ?: ?: 3//2
echo ?: ?: ?: 3//3
?>

It works just as expected, returning the first non-false value within a group of expressions.
2010-02-02 00:32:04
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
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)
2011-07-10 10:48:55
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
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
2015-06-21 23:12:37
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
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.
?>
2017-11-23 14:16:51
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
Searching for "double question mark" operator should find this page (and hopefully after this comment the crawlers will agree)
2019-09-16 20:00:43
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
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
2020-01-23 08:59:59
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
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.
2021-04-25 13:56:46
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
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)
2022-08-06 16:05:56
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Please note that using the null coalescing operator to check properties on a class that has the __get magic method (without an __isset magic method) invokes the magic method. 

For example:

<?php

class A
{
    public function 
__get($property)
    {
        echo 
'Called __get for ' $property PHP_EOL;
    }
}

$a = new A();

echo 
'Trying null coalescing operator' PHP_EOL;
$b $a->test ?? 5;

echo 
'Trying isset()' PHP_EOL;
if (isset(
$a->test)) {
   
$b $a->test;
} else {
   
$b 5;
}

?>
2023-03-24 23:50:58
http://php5.kiev.ua/manual/ru/language.operators.comparison.html
Автор:
Between the "shortcut ternary" (aka "elvis") and "spaceship" operators, you can write some quite compact comparison functions for usort and its ilk.

If you want to sort an array of associative arrays by several different keys you can chain them in the same way that you can list column names in an SQL ORDER BY clause.

<?php
usort
($array, fn($a$b) => $a['a'] <=> $b['a']
                         ?: 
$b['b'] <=> $a['b']
                         ?: 
$a['c'] <=> $b['c']);
?>
Will sort the array by column 'a', then by column 'b' descending, then by column 'c'; or in SQL-speak 'ORDER BY a, b DESC, c".
2023-08-15 09:15:45
http://php5.kiev.ua/manual/ru/language.operators.comparison.html

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