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Booleans

Description

The bool type only has two values, and is used to express a truth value. It can be either true or false.

Example: bool type

<?php

$someRight = true;
$someWrong = false;

print("Information:\n");
var_dump($someRight);
print('Type: ' . gettype($someRight) . PHP_EOL);
print("As string: {$someRight}\n\n");

print("Information:\n");
var_dump($someWrong);
print('Type: ' . gettype($someWrong) . PHP_EOL);
print("As string: {$someWrong}\n\n");

Result (PHP 8.4):

Information:
bool(true)
Type: boolean
As string: 1

Information:
bool(false)
Type: boolean
As string:

Source code: Example

Booleans as singleton types

Singleton types are those which allow only one value. PHP has support for two singleton types: false as of PHP 8.0.0 and true as of PHP 8.2.0.

Warning

Prior to PHP 8.2.0 the false type could only be used as part of a union type.

Note: It is not possible to define custom singleton types. Consider using an enumerations instead.

– PHP Reference

Syntax

To specify a bool literal, use the constants true or false. Both are case-insensitive.

<?php
$foo = True; // assign the value TRUE to $foo
?>

Typically, the result of an operator which returns a bool value is passed on to a control structure.

<?php
$action = "show_version";
$show_separators = true;

// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
    echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
    echo "<hr>\n";
}
?>

Example: bool syntax and case sensitivity

<?php

$someRight = true;
$otherRight = TRUE;
$anotherRight = True;

print("true: ");
var_dump($someRight);

print("TRUE: ");
var_dump($otherRight);

print("True: ");
var_dump($anotherRight);

print(PHP_EOL);

$someWrong = false;
$otherWrong = FALSE;
$anotherWrong = False;

print("false: ");
var_dump($someWrong);

print("FALSE: ");
var_dump($otherWrong);

print("False: ");
var_dump($anotherWrong);

print(PHP_EOL);

Result (PHP 8.4):

true: bool(true)
TRUE: bool(true)
True: bool(true)

false: bool(false)
FALSE: bool(false)
False: bool(false)

Source code: Example

Usage

Example: Comparison result use case

<?php

$input = "secret";
$password = "secret";
$isValid = ($input === $password);

if ($isValid) {
    echo "Access granted.\n";
}

Result (PHP 8.4):

Access granted.

Source code: Example

Example: Control structures use case

<?php

$isSunny = true;

if ($isSunny) {
    echo "Go outside!\n";
} else {
    echo "Stay indoors.\n";
}

Result (PHP 8.4):

Go outside!

Source code: Example

Testing for `bool`

Example: Testing for bool

<?php

$someRight = true;

print('Type of right: ' . gettype($someRight) . PHP_EOL);
print('Is bool? ' . (is_bool($someRight) ? 'yes' : 'no') . PHP_EOL . PHP_EOL);

$someWrong = false;

print('Type of wrong: ' . gettype($someWrong) . PHP_EOL);
print('Is bool? ' . (is_bool($someWrong) ? 'yes' : 'no') . PHP_EOL . PHP_EOL);

$someValue = 10;

print('Type of value: ' . gettype($someValue) . PHP_EOL);
print('Is bool? ' . (is_null($someValue) ? 'yes' : 'no') . PHP_EOL . PHP_EOL);

Result (PHP 8.4):

Type of right: boolean
Is bool? yes

Type of wrong: boolean
Is bool? yes

Type of value: integer
Is bool? no

Source code: Example

Logical context

<?php

$age = 22;
$hasId = true;
$isCitizen = false;
$technologies = [
    'C++',
    'Java',
    'PHP',
    'Docker',
    'Git',
];

print("Age: {$age}, Has ID: " . ($hasId ? 'yes' : 'no') . ", Citizen: " . ($isCitizen ? 'yes' : 'no') . "\n");

if ($age >= 18 && $hasId) {
    print("Passed age and ID check.\n");
} else {
    print("Failed age or ID check.\n");
}

if (!$isCitizen || $age < 18) {
    print("Cannot vote due to citizenship or age.\n");
}

$status = ($age >= 18 && $isCitizen && $hasId) ? "Eligible" : "Ineligible";
print("Status: $status\n");

print("Skills:\n");

while($technology = current($technologies)) {
    print($technology . ' ');
    next($technologies);
}

print(PHP_EOL);

Result (PHP 8.4):

Age: 22, Has ID: yes, Citizen: no
Passed age and ID check.
Cannot vote due to citizenship or age.
Status: Ineligible
Skills:
C++ Java PHP Docker Git

Source code: Example

Example: Logical context and equal operator

<?php

$someAnswer = true;

if ($someAnswer == true) {
    print("That's true.\n");
}

if ($someAnswer) {
    print("You're right.\n");
}

Result (PHP 8.4):

That's true.
You're right.

Source code: Example

Casting to `bool`

To explicitly convert a value to bool, use the (bool) cast. Generally this is not necessary because when a value is used in a logical context it will be automatically interpreted as a value of type bool.

When converting to bool, the following values are considered false:

the boolean false itself
the integer 0 (zero)
the floats 0.0 and -0.0 (zero)
the empty string "", and the string "0"
an array with zero elements
the unit type NULL (including unset variables)

Internal objects that overload their casting behaviour to bool. For example: SimpleXML objects created from empty elements without attributes. Every other value is considered true (including resource and NAN).

Warning

-1 is considered true, like any other non-zero (whether negative or positive) number!

Example: Casting to boolean

<?php
var_dump((bool) "");        // bool(false)
var_dump((bool) "0");       // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>

– PHP Reference

Example: Casting to bool

<?php

$someNothing = null;
$nullToBool = (bool) $someNothing;
print("null to bool: ");
var_dump($nullToBool);

print(PHP_EOL);

$someNumber = 0;
$intToBool = (bool) $someNumber;
print("{$someNumber} to bool: ");
var_dump($intToBool);

$someNumber = -0;
$intToBool = (bool) $someNumber;
print("-0 to bool: ");
var_dump($intToBool);

$someNumber = 1;
$intToBool = (bool) $someNumber;
print("{$someNumber} to bool: ");
var_dump($intToBool);

$someNumber = -1;
$intToBool = (bool) $someNumber;
print("{$someNumber} to bool: ");
var_dump($intToBool);

$someNumber = 3;
$intToBool = (bool) $someNumber;
print("{$someNumber} to bool: ");
var_dump($intToBool);

print(PHP_EOL);

$someMeasure = 0.0;
$floatToBool = (bool) $someMeasure;
print("0.0 to bool: ");
var_dump($floatToBool);

$someMeasure = -0.0;
$floatToBool = (bool) $someMeasure;
print("-0.0 to bool: ");
var_dump($floatToBool);

$someMeasure = 0.1;
$floatToBool = (bool) $someMeasure;
print("{$someMeasure} to bool: ");
var_dump($floatToBool);

$someMeasure = 1.0;
$floatToBool = (bool) $someMeasure;
print("1.0 to bool: ");
var_dump($floatToBool);

$someMeasure = 3.0;
$floatToBool = (bool) $someMeasure;
print("3.0 to bool: ");
var_dump($floatToBool);

print(PHP_EOL);

$someText = "";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = " ";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "false";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "true";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "0";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "-0";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "1";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "-1";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "null";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

$someText = "a";
$stringToBool = (bool) $someText;
print("\"{$someText}\" to bool: ");
var_dump($stringToBool);

print(PHP_EOL);

$someCollection = [];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [true];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [false];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [0];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [1];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [''];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

$someCollection = [null];
$arrayToBool = (bool) $someCollection;
print("[] to bool: ");
var_dump($arrayToBool);

print(PHP_EOL);

Result (PHP 8.4):

null to bool: bool(false)

0 to bool: bool(false)
-0 to bool: bool(false)
1 to bool: bool(true)
-1 to bool: bool(true)
3 to bool: bool(true)

0.0 to bool: bool(false)
-0.0 to bool: bool(false)
0.1 to bool: bool(true)
1.0 to bool: bool(true)
3.0 to bool: bool(true)

"" to bool: bool(false)
" " to bool: bool(true)
"false" to bool: bool(true)
"true" to bool: bool(true)
"0" to bool: bool(false)
"-0" to bool: bool(true)
"1" to bool: bool(true)
"-1" to bool: bool(true)
"null" to bool: bool(true)
"a" to bool: bool(true)

[] to bool: bool(false)
[] to bool: bool(true)
[] to bool: bool(true)
[] to bool: bool(true)
[] to bool: bool(true)
[] to bool: bool(true)
[] to bool: bool(true)

Source code: Example

Casting from `bool`

<?php

$someRight = true;
$someWrong = false;

$trueToInt = (int) $someRight;
print("True to int: ");
var_dump($trueToInt);
$falseToInt = (int) $someWrong;
print("False to int: ");
var_dump($falseToInt);
print(PHP_EOL);

$trueToFloat = (float) $someRight;
print("True to float: ");
var_dump($trueToFloat);
$falseToFloat = (float) $someWrong;
print("False to float: ");
var_dump($falseToFloat);
print(PHP_EOL);

$trueToString = (string) $someRight;
print("True to string: ");
var_dump($trueToString);
$falseToString = (string) $someWrong;
print("False to string: ");
var_dump($falseToString);
print(PHP_EOL);

$trueToArray = (array) $someRight;
print("True to array: ");
var_dump($trueToArray);
$falseToArray = (array) $someWrong;
print("False to array: ");
var_dump($falseToArray);
print(PHP_EOL);

$trueToObject = (object) $someRight;
print("True to object: ");
var_dump($trueToObject);
$falseToObject = (object) $someWrong;
print("False to object: ");
var_dump($falseToObject);
print(PHP_EOL);

Result (PHP 8.4):

True to int: int(1)
False to int: int(0)

True to float: float(1)
False to float: float(0)

True to string: string(1) "1"
False to string: string(0) ""

True to array: array(1) {
  [0]=>
  bool(true)
}
False to array: array(1) {
  [0]=>
  bool(false)
}

True to object: object(stdClass)#1 (1) {
  ["scalar"]=>
  bool(true)
}
False to object: object(stdClass)#2 (1) {
  ["scalar"]=>
  bool(false)
}

Source code: Example

Automatic conversion to `bool`

<?php

$i = 0;
print("\$i = 0; // (" . gettype($i) . ")\n");
if ($i) print "casted to true\n";
else print "casted to false\n";

$i = 1;
print("\$i = 1; // (" . gettype($i) . ")\n");
if ($i) print "casted to true\n";
else print "casted to false\n";

$i = 3;
print("\$i = 3; // (" . gettype($i) . ")\n");
if ($i) print "casted to true\n";
else print "casted to false\n";

$i = -3;
print("\$i = -3; // (" . gettype($i) . ")\n");
if ($i) print "casted to true\n";
else print "casted to false\n";

print PHP_EOL;

$d = 0.0;
print("\$d = 0.0; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = -0.0;
print("\$d = -0.0; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = 1.0;
print("\$d = 1.0; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = 3.0;
print("\$d = 3.0; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = -3.0;
print("\$d = -3.0; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = 0.1;
print("\$d = 0.1; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = 3.14;
print("\$d = 3.14; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

$d = -3.14;
print("\$d = -3.14; // (" . gettype($d) . ")\n");
if ($d) print "casted to true\n";
else print "casted to false\n";

print PHP_EOL;

$s = "";
print("\$s = \"\"; // empty string (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = " ";
print("\$s = \" \"; // space (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = "0";
print("\$s = \"0\"; // empty string (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = "\0";
print("\$s = \"\\0\"; // null (\\0) character (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = "a";
print("\$s = \"a\"; // (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = "false";
print("\$s = \"false\"; // (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

$s = "true";
print("\$s = \"true\"; // (" . gettype($s) . ")\n");
if ($s) print "casted to true\n";
else print "casted to false\n";

print PHP_EOL;

$a = [];
print("\$a = []; // (" . gettype($a) . ")\n");
if ($a) print "casted to true\n";
else print "casted to false\n";

$a = [0];
print("\$a = [0]; // (" . gettype($a) . ")\n");
if ($a) print "casted to true\n";
else print "casted to false\n";

$a = [null];
print("\$a = [null]; // (" . gettype($a) . ")\n");
if ($a) print "casted to true\n";
else print "casted to false\n";

Result (PHP 8.4):

$i = 0; // (integer)
casted to false
$i = 1; // (integer)
casted to true
$i = 3; // (integer)
casted to true
$i = -3; // (integer)
casted to true

$d = 0.0; // (double)
casted to false
$d = -0.0; // (double)
casted to false
$d = 1.0; // (double)
casted to true
$d = 3.0; // (double)
casted to true
$d = -3.0; // (double)
casted to true
$d = 0.1; // (double)
casted to true
$d = 3.14; // (double)
casted to true
$d = -3.14; // (double)
casted to true

$s = ""; // empty string (string)
casted to false
$s = " "; // space (string)
casted to true
$s = "0"; // empty string (string)
casted to false
$s = "\0"; // null (\0) character (string)
casted to true
$s = "a"; // (string)
casted to true
$s = "false"; // (string)
casted to true
$s = "true"; // (string)
casted to true

$a = []; // (array)
casted to false
$a = [0]; // (array)
casted to true
$a = [null]; // (array)
casted to true

Source code: Example

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php.lab

Booleans

Description

Booleans as singleton types

Syntax

Usage

Testing for bool

Logical context

Casting to bool

Casting from bool

Automatic conversion to bool

Testing for `bool`

Casting to `bool`

Casting from `bool`

Automatic conversion to `bool`