# W3cubDocs

/PHP

## 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.
\$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:

```<?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;
}
?>```
```<?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).

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 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 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(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

```<?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
}
?>```
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`.

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 to avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious compared to other languages. Indeed prior to PHP 8.0.0, ternary expressions were evaluated from left to right, instead of right to left like most other programming languages.

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' prior to PHP 8.0.0
// 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, 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.
?>```

### Null Coalescing Operator

Further exists the "??" (or null coalescing) operator.

Example #5 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';
}

?>```
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:

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

?>```

© 1997–2020 The PHP Documentation Group
Licensed under the Creative Commons Attribution License v3.0 or later.
https://www.php.net/manual/en/language.operators.comparison.php
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